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  • 1. Ammerman, J.W.
    et al.
    Fuhrman, J.A.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Azam, F.
    Bacterioplankton growth in seawater: I.Growth kinetics and cellular characteristics in seawater cultures1984In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 18, p. 31-39Article in journal (Refereed)
  • 2. Andersson, A.
    et al.
    Falk, S.
    Samuelsson, G.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Nutritional characteristics of a mixitropic nanoflagellate, Ochromonas sp.1989In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 17, p. 117-128Article in journal (Refereed)
  • 3. Andersson, A.
    et al.
    Heacky, P.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Effect of Temperature and Light on the Growth of Micro- Nano- and Picoplankton: Impact on Algal Succession.1994In: Marine Biology, ISSN 1230-7688Article in journal (Refereed)
  • 4. Andersson, A.
    et al.
    Selstam, E.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Vertical Transport of Lipid in Sea Water.1993In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 98, p. 149-155Article in journal (Refereed)
  • 5.
    Andersson, Agneta
    et al.
    Department of Microbiology. University of Urnea. S-901 87 UMEA, Sweden.
    Lee, C.
    Azam, F.
    Hagström, Åke
    Department of Microbiology. University of Urnea. S-901 87 UMEA, Sweden.
    Release of aminoacids and inorganic nutrients by heterotrophic marine microflagellates1985In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 23, p. 99-106Article in journal (Refereed)
    Abstract [en]

    Heterotrophic microflagellates isolated from the Baltic Sea and grown under laboratoryconditions were shown to release dissolved free amino acids (DFAA) when grazing bacteria. Flagellatesreleased 3H-amino acids when fed 3H-leucine-labelled bacteria, and concentrations of aminoacids increased in the experimental medium. Serine showed a strong positive correlation withflagellate feeding. Aspartic acid, glutamic acid and ornithine also increased more than other aminoacids. During consumption of bacteria, the flagellates released 13% of the ingested nitrogen asammonia, and 30 % of the ingested phosphorus as phosphate. In a field experiment off Scripps Pier, wemeasured bacterial production, flagellate abundance, and concentration of DFAA over a 28 h period.The concentration of DFAA showed a covariation with the flagellate numbers. Results from our fieldand laboratory experiments suggest that flagellates may be a source of DFAA in the sea. 

  • 6. Azam, F.
    et al.
    Ammerman, J.W.
    Fuhrman, J.A.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Role of bacteria in polluted marine ecosystems. ed R Colwell1983In: Proceedings of Workshop on meaningful measures of marine pollution effects NOAA, 1983Conference paper (Other academic)
  • 7. Azam, F.
    et al.
    Smith, D.C.
    Steward, G.F.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Bacteria-organic-matter coupling and its significance for oceanic carboncycling.1993In: Microbial Ecology, ISSN 0095-3628, E-ISSN 1432-184X, Vol. 28, p. 167-179Article in journal (Refereed)
  • 8. Blackburn, N.
    et al.
    Azam, F.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Spatially explicit simulations of a microbial food web.1997In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 42, p. 613-622Article in journal (Refereed)
  • 9. Blackburn, N.
    et al.
    Wikner, J.
    Cuadros Hanson, R.
    Bjørnsen, K.P.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Rapid determination of bacterial abundance, biovolume, morpology and growth by neural network based image analysis.1998In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 64, p. 3246-3255Article in journal (Refereed)
  • 10. Blackburn, N.
    et al.
    Zweifel, Ulla Li
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Cycling of marine dissolved organic matter: II. A model analysis.1996In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 11, p. 79-90Article in journal (Refereed)
  • 11.
    Boström, Kjärstin H.
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Reimann, Lasse
    Kühl, Michael
    Hagström, Åke
    Isolation and gene quantification of heterotrophic N2-fixing bacterioplankton in the Baltic Sea2007In: Environmental Microbiology, ISSN 1462-2912, E-ISSN 1462-2920, Vol. 9, no 1, p. 152-164Article in journal (Refereed)
  • 12.
    Boström, Kjärstin H.
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Riemann, Lasse
    Zweifel, Ulla Li
    Hagström, Åke
    Nodularia sp. nifH gene transcripts in the Baltic Sea proper2007In: Journal of Plankton Research, ISSN 0142-7873, E-ISSN 1464-3774, Vol. 29, no 4, p. 391-399Article in journal (Refereed)
  • 13.
    Boström, Kjärstin
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Simu, Karin
    Hagström, Åke
    Riemann, Lasse
    Optimization of DNA extraction for quantitative marine bacterioplankton community analysis2004In: Limnology and oceanography: methods, Vol. 2, p. 365-373Article in journal (Refereed)
  • 14. Dahlbäck, B.
    et al.
    Gunnarsson, L.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Mikrobiologiska aspekter på musselodling1983In: Odling av blåmusslor / [ed] Rutger Rosenberg, Lund: Signum , 1983, p. 60-67Chapter in book (Other academic)
  • 15.
    Dupont, Chris L.
    et al.
    J. Craig Venter Institute, USA.
    Larsson, John
    Stockholm University.
    Yooseph, Shibu
    J. Craig Venter Institute, USA.
    Ininbergs, Karolina
    Stockholm University.
    Goll, Johannes
    J. Craig Venter Institute, USA.
    Asplund-Samuelsson, Johannes
    Stockholm University.
    McCrow, John P.
    J. Craig Venter Institute, USA.
    Celepli, Narin
    Stockholm University.
    Allen, Lisa Zeigler
    J. Craig Venter Institute, USA.
    Ekman, Martin
    Stockholm University.
    Lucas, Andrew J.
    Hagström, Åke
    University of Gothenburg.
    Thiagarajan, Mathangi
    Brindefalk, Bjorn
    Richter, Alexander R.
    Andersson, Anders F.
    Tenney, Aaron
    Lundin, Daniel
    KTH Royal Institute of Technology.
    Tovchigrechko, Andrey
    Nylander, Johan A. A.
    Brami, Daniel
    Badger, Jonathan H.
    Allen, Andrew E.
    Rusch, Douglas B.
    Hoffman, Jeff
    Norrby, Erling
    Friedman, Robert
    Pinhassi, Jarone
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Venter, J. Craig
    Bergman, Birgitta
    Functional Tradeoffs Underpin Salinity-Driven Divergence in Microbial Community Composition2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 2, article id e89549Article in journal (Refereed)
    Abstract [en]

    Bacterial community composition and functional potential change subtly across gradients in the surface ocean. In contrast, while there are significant phylogenetic divergences between communities from freshwater and marine habitats, the underlying mechanisms to this phylogenetic structuring yet remain unknown. We hypothesized that the functional potential of natural bacterial communities is linked to this striking divide between microbiomes. To test this hypothesis, metagenomic sequencing of microbial communities along a 1,800 km transect in the Baltic Sea area, encompassing a continuous natural salinity gradient from limnic to fully marine conditions, was explored. Multivariate statistical analyses showed that salinity is the main determinant of dramatic changes in microbial community composition, but also of large scale changes in core metabolic functions of bacteria. Strikingly, genetically and metabolically different pathways for key metabolic processes, such as respiration, biosynthesis of quinones and isoprenoids, glycolysis and osmolyte transport, were differentially abundant at high and low salinities. These shifts in functional capacities were observed at multiple taxonomic levels and within dominant bacterial phyla, while bacteria, such as SAR11, were able to adapt to the entire salinity gradient. We propose that the large differences in central metabolism required at high and low salinities dictate the striking divide between freshwater and marine microbiomes, and that the ability to inhabit different salinity regimes evolved early during bacterial phylogenetic differentiation. These findings significantly advance our understanding of microbial distributions and stress the need to incorporate salinity in future climate change models that predict increased levels of precipitation and a reduction in salinity.

  • 16.
    Farnelid, Hanna
    et al.
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Andersson, Anders F.
    Bertilsson, Stefan
    Al-Soud, Waleed Abu
    Hansen, Lars H
    Sørensen, Søren
    Steward, Grieg F
    Hagström, Åke
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Riemann, Lasse
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences. Marine Biological Section, Department of Biology, University of Copenhagen, Helsingør, Denmark.
    Nitrogenase gene amplicons from global marine surface waters are dominated by genes of non-cyanobacteria2011In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 6, no 4, p. e19223-Article in journal (Refereed)
    Abstract [en]

    Cyanobacteria are thought to be the main N(2)-fixing organisms (diazotrophs) in marine pelagic waters, but recent molecular analyses indicate that non-cyanobacterial diazotrophs are also present and active. Existing data are, however, restricted geographically and by limited sequencing depths. Our analysis of 79,090 nitrogenase (nifH) PCR amplicons encoding 7,468 unique proteins from surface samples (ten DNA samples and two RNA samples) collected at ten marine locations world-wide provides the first in-depth survey of a functional bacterial gene and yield insights into the composition and diversity of the nifH gene pool in marine waters. Great divergence in nifH composition was observed between sites. Cyanobacteria-like genes were most frequent among amplicons from the warmest waters, but overall the data set was dominated by nifH sequences most closely related to non-cyanobacteria. Clusters related to Alpha-, Beta-, Gamma-, and Delta-Proteobacteria were most common and showed distinct geographic distributions. Sequences related to anaerobic bacteria (nifH Cluster III) were generally rare, but preponderant in cold waters, especially in the Arctic. Although the two transcript samples were dominated by unicellular cyanobacteria, 42% of the identified non-cyanobacterial nifH clusters from the corresponding DNA samples were also detected in cDNA. The study indicates that non-cyanobacteria account for a substantial part of the nifH gene pool in marine surface waters and that these genes are at least occasionally expressed. The contribution of non-cyanobacterial diazotrophs to the global N(2) fixation budget cannot be inferred from sequence data alone, but the prevalence of non-cyanobacterial nifH genes and transcripts suggest that these bacteria are ecologically significant.

  • 17. Fuhrman, J.
    et al.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Bacterial community structure and its patterns.2008In: Microbial ecology of the oceans / [ed] Kirchman, D, New York: Wiley , 2008, 2nd, p. 45-90Chapter in book (Other academic)
  • 18. Fuhrman, J.A.
    et al.
    Comeau, D.E.
    Hagström, Åke
    Department of Microbiology, University of Umeå.
    Chan, A.M.
    Extraction from natural planktonic microorganisms of DNA suitable for molecular biological studies1988In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 54, no 6, p. 1426-1429Article in journal (Refereed)
    Abstract [en]

    We developed a simple technique for the high-yield extraction of purified DNA from mixed populations ofnatural planktonic marine microbes (primarily bacteria). This is a necessary step for several molecularbiological approaches to the study of microbial communities in nature. The microorganisms from near-shoremarine and brackish water samples, ranging in volume from 8 to 40 liters, were collected on 0.22-,um-pore-sizefluorocarbon-based filters, after prefiltration through glass fiber filters, to remove most of the eucaryotes. DNAwas extracted directly from the filters in 1% sodium dodecyl sulfate that was heated to 95 to 100°C for 1.5 to2 min. This procedure lysed essentially all the bacteria and did not significantly denature the DNA. The DNAwas purified by phenol extraction, and precautions were taken to minimize shearing. Agarose gel electrophoresisshowed that most of the final preparation had a large molecular size (>23 kilobase pairs). The DNA wassufficiently pure to allow complete digestion by the restriction endonuclease Sau3AI and ligation to vector DNA.In a sample in which the extracted DNA was quantified by binding to the dye Hoechst H33258, DNA wasquantitatively extracted, and 45% of the initially extracted DNA was recovered after purification. Final yieldswere a few micrograms of DNA per liter of seawater and were roughly 25 to 50% of the total bacterial DNAin the sample. Alternatives to the initial harvest by filtration method, including continuous-flow centrifugationand thin-channel or hollow-fiber concentration followed by centrifugation, were less efficient than filtration interms of both time and yield, largely because of the difficulty of centrifuging the very small bacteria typical ofmarine plankton. These methods were judged to be less appropriate for studies of natural populations as theyimpose a strong selection for the larger bacteria. 

  • 19. Fuhrman, J.A.
    et al.
    Eppley, R.W.
    Hagström, Åke
    Department of Microbiology. University of Urnea. S-901 87 UMEA, Sweden.
    Azam, F.
    Diel variations in bacterioplankton, phytoplankton, and related parameters in the Southern California Bight.1985In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 27, p. 9-20Article in journal (Refereed)
    Abstract [en]

    The principal objectives of this study were (i) to determine the extent of coupling betweenphytoplankton and microheterotrophs on the shelf off Southern California. (ii) to compare differentmeasures of primary and bacterial secondary production, and (iii) to assess whether sampling timesshould be as strictly controlled for microheterotroph as for autotroph studies. Two diel cycles (May andOctober) were studied by sampling an isotherm as the ship followed paired submerged drogues. Wefound significant die1 changes of chlorophyll, 14C bicarbonate incorporation, bacterial abundance andthymidine incorporation, frequency of dividing bacterial cells (FDC), abundance of non-pigmentedflagellates, particulate organic carbon and nitrogen and their ratios, and dissolved oxygen. Theseparameters all had higher values dunng daylight hours than at night, showing close coupling betweenthe phytoplankton (light-forced) and the microheterotrophs. The ratio of in vivo to extractedchlorophyll a fluorescence, however, displayed a maximum at midnight and minimum at midday,suggesting an endogenous rhythm. Primary production measured by the 14C method was similar to netproduction inferred from in situ oxygen changes. Short-lived peaks in FDC values suggested partlysynchronized bacterial division. 

  • 20. Gasol, J.M.
    et al.
    Zweifel, Ulla Li
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Peters, F.
    Fuhrman, J.A.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Significance of size and nucleic acid content heterogeneity as measured by flow cytometry in natural planktonic bacteria.1999In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 65, p. 4475-4483Article in journal (Refereed)
  • 21.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Aquatic bacteria: Measurements and significance of growth1984In: Current perspectives in microbial ecology: Proceedings of the Third International Symposium on Microbial Ecology, Michigan State University, [East Lansing] 7-12 August 1983 / [ed] MJ Klug & CA Reddy, Washington,D.C: ASM , 1984, p. 495-501Chapter in book (Other academic)
  • 22.
    Hagström, Åke
    Umeå universitet.
    Bacterial growth in situ a study in aquatic microbiology1978Doctoral thesis, monograph (Other academic)
  • 23.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Microbial degradation of hydrocarbon in natural seawater1987In: Baltic Marine biologists 4th meeting, Gdansk, 1987Conference paper (Other academic)
  • 24.
    Hagström, Åke
    The National Environmental Protection Board, Brackish Water Toxicology Laboratory, Studsvik, S-611 01 Nyköping, Sweden.
    The fate of oil in a model ecosystem1977In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 6, no 4, p. 229-231Article in journal (Refereed)
  • 25.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Till sjöss med bakterier och vetenskap1984Other (Other academic)
  • 26.
    Hagström, Åke
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Ammerman, J.W.
    Henrichs, S.
    Azam, F.
    Bacterioplankton growth in seawater: II. Organic matter utilization during steady-state growth in seawater cultures1984In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 18, p. 41-48Article in journal (Refereed)
  • 27.
    Hagström, Åke
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Andersson, A.
    Larsson, U.
    Size-selective grazing by a microflagellate on pelagic bacteria1986In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 33, p. 51-57Article in journal (Refereed)
  • 28.
    Hagström, Åke
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Andersson, A.
    Öquist, G.
    Algal and bacterial production in a coastal area (Norrbyn) of the northern Bothnian Sea1983In: Aquilo. Ser. Zoologica, ISSN 0570-5177, Vol. 22, p. 131-137Article in journal (Refereed)
  • 29.
    Hagström, Åke
    et al.
    Department of Microbiology, University of Umeå.
    Azam, F.
    Andersson, A.
    Wikner, J.
    Rassoulzadegan, F.
    Microbial loop in an oligotrophic pelagic marine ecosystem: Possible roles of cyanobacteria and nanoflagellates in the organic fluxes1988In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 49, p. 171-178Article in journal (Refereed)
    Abstract [en]

    In an attempt to quantify the organic fluxes within the microbial loop of oligotrophicMediterranean water, organic pools and production rates were monitored. The production of cyanobacteriaand its dynamics dominated the overall productivity in the system. The largest standing stock wasthat of the bacterioplankton and its growth consumed 8.3 pg C 1-' d-', hence about 60 % of the primaryproduction was required for bacterial growth. Using the MiniCap technique, we measured a predationon bacteria of 2 6 X 104 bacteria ml-' h-'. This was in good agreement with the bacterial production rateof 2.3 X 104 cells rnl-' h-' Thus, growth and predation were balanced for heterotrophic bacterioplankton.Almost all of this predation on bacteria was due to organisms passing a 12 vm Nuclepore filter. Thisraises the question of what mechanisms channel 60 % of primary production into bacteria. We thereforeoutlined a mass-balance model to illustrate routes that could explain this transfer. According to ourmodel the main flux route is cyanobacteria and concomitantly consumed heterotrophic bacteria carboninto bacterivores. A substantial fraction of the bacterivore and the microplankton carbon is released byexcretion and/or cell lysis, to be used by the heterotrophic bacterioplankton. About 86% of theautotrophic production is balanced by respiration due to heterotrophic bacteria and protozoa, leaving6 % of the primary production to higher trophic levels. This scenario should apply to ecosystems wherebacterial production rate is high and comparable to primary production, and the dominant primaryproducers are cyanobacteria. A significant fraction of the photosynthetically fixed carbon will bemineralized within a simple microbial loop, thus rendering it an energy sink in the foodweb.

  • 30.
    Hagström, Åke
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Azam, F.
    Kuparinen, J.
    Zweifel, Ulla Li
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Pelagic plankton growth and resource limitations in the Baltic Sea2001In: A Systems Analysis of the Baltic Sea / [ed] F.V. Wulff, L.A. Rahm, P. Larsson, Berlin Heidelberg: Springer, 2001, p. 177-210Chapter in book (Other academic)
  • 31.
    Hagström, Åke
    et al.
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Azam, Farooq
    Univ Calif San Diego, USA.
    Berg, Carlo
    Linnaeus University, Faculty of Health and Life Sciences, Department of Biology and Environmental Science.
    Zweifel, Ulla Li
    University of Gothenburg.
    Isolates as models to study bacterial ecophysiology and biogeochemistry2018In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 80, no 1, p. 15-27Article in journal (Refereed)
    Abstract [en]

    Here, we examine the use of bacterial isolates growing in artificial media or seawater as a means to investigate bacterial activity in the upper ocean. The discovery of a major role of bacteria in the ocean's carbon cycle owes greatly to the development of culture-independent assemblage-level approaches; however, this should not detract from the recognition of model isolates as representing the environmental microbiome. A long-established tool for culturing bacteria, in medicine and general microbiology, has been agar plates. In addition, a great variety of liquid substrates including seawater have been used to successfully identify and cultivate important bacteria such as Pelagibacter ubique. Yet, the discrepancy between microscopic counts and plate counts, the great plate count anomaly, has led to a biased perception of the limited relevance of isolated bacteria. Linking isolates to whole-genome sequencing, phylogenetic analysis and computational modeling will result in culturable model bacteria from different habitats. Our main message is that bacterial ecophysiology, particularly growth rates in seawater, and functionalities inferred through the identity, abundance and expression of specific genes could be mechanistically linked if more work is done to isolate, culture and study bacteria in pure cultures. When we rally behind a strategy aimed at culturing targeted phenotypes, we are not saying that culture independent studies of bacteria in the sea are not informative. We are suggesting that culturebased studies can help integrate the ecological and genomic views.

  • 32.
    Hagström, Åke
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Gissel-Nielsen, T.
    Kerulf, J.
    Forbes, T.
    Havets usynlige liv1996Report (Other academic)
  • 33.
    Hagström, Åke
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Horrigan, S.G.
    Norrman, B.
    Wikner, J.
    Critical processes in transformation of nitrogen and phosphorus in the pelagic ecosystem1990In: Large-scale environmental effects and ecological processes in the Baltic Sea: Research Programme for the Period 1990-1995and Background Documents / [ed] Fredrik Wulff, Swedish Environ Protection Agency , 1990, p. 110-128Chapter in book (Other academic)
  • 34.
    Hagström, Åke
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Larsson, U.
    Diel and seasonal variation in growth rates of pelagic bacteria1984Other (Other academic)
  • 35.
    Hagström, Åke
    et al.
    The National Environmental Protection Board, Brackish Water Toxicology Laboratory, Studsvik, S-611 01 Nyköping.
    Larsson, U.
    Hörstedt, P.
    Normark, S.
    Frequency of dividing cells a new approach to the determination of bacterial growth rates in aquatic environments1979In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 37, no 5, p. 805-812Article in journal (Refereed)
    Abstract [en]

    Frequency of dividing cells is suggested to be an indirect measureof the mean growth rate of an aquatic bacterial community. Seasonalchanges in frequency of dividing cells were found which covariatedwith the bacterial uptake of 14C-labeled phytoplankton exudates.Batch and continuous culture growth experiments, using brackishwater bacteria in pure and mixed enrichment cultures, were performedto establish a relationship between frequency of dividing cellsand growth rate. An improved technique for bacterial directcounts, using fluorescent staining and epifluorescence microscopy,is presented. Based on a 6-month survey in a coastal area ofthe Baltic Sea, the bacterial production in the photic zoneis estimated. Compared to the total primary production in thearea, the bacterial population during this period utilized approximately25% of the amount of carbon originally fixed by the primaryproducers.

  • 36.
    Hagström, Åke
    et al.
    Swedish Water and Air Pollution Research Laboratory, Box 5607,S-114 86 Stockholm, Sweden.
    Normark, S.
    Toxic effect and action of chlorinated by-products from vinyl chloride production on Escherichia coli K-121974In: Ambio, ISSN 0044-7447, E-ISSN 1654-7209, Vol. 3, no 2, p. 77-79Article in journal (Refereed)
  • 37.
    Hagström, Åke
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Pinhassi, Jarone
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Zweifel, Ulla Li
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Biogeographical diversity among marine bacterioplankton2000In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 21, p. 231-244Article in journal (Refereed)
  • 38.
    Hagström, Åke
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Pinhassi, Jarone
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Zweifel, Ulla Li
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Marine bacterioplankton show bursts of rapid growth induced by substrate shifts2001In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 24, p. 109-115Article in journal (Refereed)
  • 39.
    Hagström, Åke
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Pommier, Thomas
    Dembinska, D.
    Rohwer, F.
    Simu, Karin
    Zweifel, Ulla Li
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Use of 16S rDNA for species delineation of marine bacterioplankton.2002In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 68, p. 3628-3633Article in journal (Refereed)
  • 40.
    Hagström, Åke
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Pommier, Thomas
    Rohwer, F
    Simu, Karin
    Stolte, Willem
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Svensson, D
    Zweifel, Ulla Li
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Use of 16S ribosomal DNA for delineation of marine bacterioplankton species.2002In: Applied and Environmental Microbiology, Vol. 68, p. 3628-3633Article in journal (Refereed)
  • 41.
    Hagström, Åke
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Wennergren, G.
    Simulerade oljespill, aspekter på "weathering" av olika oljor1974In: Svenska Havsforskningsföreningen, Vol. 999, p. 145-160Article in journal (Other (popular science, discussion, etc.))
  • 42. Havskum, H.
    et al.
    Thingstad, T.F.
    Scharek, R.
    Peters, F.
    Berdalet, E.
    Sala, M.M.
    Alcarazd, M.
    Bangsholt, J.C.
    Zweifel, Ulla Li
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Perez, M.
    Dolan, J.R.
    Silicate and labile DOC interfere in structuring the microbial food web via algal-bacterial competition for mineral nutrients: Results of a mesocosm experiment.2003In: Limnology and Oceanography, ISSN 0024-3590, E-ISSN 1939-5590, Vol. 48, p. 129-140Article in journal (Refereed)
  • 43. Horrigan, S.G.
    et al.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Koike, I.
    Azam, F.
    Inorganic nitrogen utilization by assemblages of marine bacteria in seawater culture1988In: Marine Ecology Progress Series, ISSN 0171-8630, E-ISSN 1616-1599, Vol. 50, p. 147-150Article in journal (Refereed)
    Abstract [en]

    Stimulation of heterotrophic bacterial growth by inorganic nitrogen (nitrate and ammonium) was observed in natural assemblages of marine bacteria growth in continuous culture with unsupplemented sea water as primary medium. In the presence of nitrogenous supplements, bacterial numbers increased approximately 3-fold. These results indicate that re-evaluation of the role of heterotrophic bacterioplankton in the pelagic nitrogen cycle may be necessary. 

  • 44.
    Hultin, Kim A. H.
    et al.
    Stockholm University.
    Krejci, Radovan
    Stockholm University.
    Pinhassi, Jarone
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Gómez-Consarnau, Laura
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Mårtensson, E. Monica
    Stockholm University.
    Hagström, Åke
    Linnaeus University, Faculty of Science and Engineering, School of Natural Sciences.
    Nilsson, E. Douglas
    Stockholm University.
    Aerosol and bacterial emissions from Baltic Seawater2011In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 99, no 1, p. 1-14Article in journal (Refereed)
    Abstract [en]

    Factors influencing the production of primary marine aerosol are of great importance to better understand the marine aerosols' impact on our climate. Bubble-bursting from whitecaps is considered the most effective mechanism for sea spray production, and a way of sea-air transfer for some bacterial species. Two coastal sites in the Baltic Sea were used to investigate aerosol and bacterial emissions from the bubble-bursting process by letting a jet of water hit a water surface within an experimental tank, mimicking the actions of breaking waves. The aerosol size distribution spectra from the two sites were similar and conservative in shape where the modes were centered at about 200 nm dry diameter. We found a distinct decrease in bubbled aerosol production with increasing water temperature. A clear diurnal cycle in bubbled aerosol production was observed, anticorrelated with both water temperature and dissolved oxygen, which to our knowledge has never been shown before. A link between decreasing aerosol production in daytime and phytoplankton activity is likely to be an important factor. Colony-forming bacteria were transferred to the atmosphere via the bubble-bursting process, with a linear relationship to their seawater concentration.

  • 45. Johansen, J.F.
    et al.
    Blackburn, N.
    Pinhassi, Jarone
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Zweifel, Ulla Li
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Large Variability in Motility Characteristics among Marine Bacteria.2002In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 28, p. 229-237Article in journal (Refereed)
  • 46. Landner, L.
    et al.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Oil spill protection in the Baltic based on investigations into the ecological effects of oil pollution and of chemicals used to combat oil spills1975In: Journal of Water Pollution Control Federation, ISSN 0043-1303, Vol. 47, p. 796-809Article in journal (Refereed)
  • 47. Larsson, U.
    et al.
    Hagström, Åke
    Department of Microbiology, University of Umeå; S-90187 Umeå, Sweden.
    Fractionated Phytoplankton Primary Production, Exudate Release and Bacterial Production in a Baltic Eutrophication Gradient1982In: Marine Biology, ISSN 1230-7688, Vol. 67, no 1, p. 57-70Article in journal (Refereed)
    Abstract [en]

    The distribution of phytoplankton primary production into four size fractions (>10 μm, 10-3 μm, 3-0.2 μm and <0.2>μm), the utilization of algal exudates by bacteria and the bacterial production were studied in a eutrophication gradient in the northern Baltic proper. The polluted area exhibits substantially increased nutrient, especially nitrogen, levels while only minor differences occur in salinity and temperature regimes. Total primary production was 160 g C · m-2 · yr-1 at the control station and about 275 g C · m-2 · yr-1 at the eutrophicated stations. The estimated total exudate release was 16% of the totally fixed 14CO2 in the control area and 12% in the eutrophicated area (including the estimated bacterial uptake of exudates). The difference in14CO2 uptake rates between incubation of previously filtered water (<3,><2,><1>μm) and unfiltered water was used to estimate bacterial uptake of phytoplankton exudates which were found to contribute about half of the estimated bacterial carbon requirement in both areas. Bacterial production was estimated by the frequency of dividing cells (FDC) method as being 38 g C · m-2 · yr-1 at the control station and 50 g C · m-2 · yr-1 at the eutrophicated stations. To estimate the mean in situ bacterial cell volume a correlation between FDC and cell volume was used. The increased annual primary production in the eutrophicated area was due mainly to higher production during spring and autumn, largely by phytoplankton cells (mainly diatoms) retained by a 10 μm filter. Primary production duringsummer was similarin the two areas, as was the distribution on different size fractions. This could possibly explain the similar bacterial production in the trophic layers at all stations since the bulk of bacterial production occurs during summer. It was demonstrated that selective filtration does not quantitatively separate photoautotrophs and bacteria. A substantial fraction of the primary production occurs in the size fraction <3>μm. The primary production encountered in the 3-0.2 μm fraction was due to abundant picoplankton (0.5 to 8 · 107 ind · l-1), easily passing a 3 μm filter. The picoplankton was estimated to constitute up to 25% of the total phytoplankton biomass in the control area and up to 10% in the eutrophicated area.

  • 48. Larsson, U.
    et al.
    Hagström, Åke
    The National Environmental Protection Board, Brackish Water Toxicology Laboratory, Studsvik, S-611 01 Nyköping.
    Phytoplankton extracellular release as an energy source for the growth of pelagic bacteria1979In: Marine Biology, ISSN 1230-7688, Vol. 52, p. 199-206Article in journal (Refereed)
  • 49. Larsson, U.
    et al.
    Linden, O.
    Hagström, Åke
    Department of Microbiology, University of Umeå .
    Al-Alawi, Z.S.
    Pelagic bacterial and phytoplankton in a subtropical marine environment exposed to chronic oil contamination.1990In: Oil and Chemical Pollution, ISSN 0269-8579, Vol. 7, no 2, p. 129-142Article in journal (Refereed)
    Abstract [en]

    The abundance and production of pelagic bacteria, phytoplankton primary production and chlorophyll content were studied in coastal waters receiving the effluent from an oil refinery in the Arabian Gulf. The area also receives unknown amounts of other effluents rich in organic matter and nutrients. The abundance of bacteria was measured by epifluorescent direct counts, and productivity was estimated by 3H-thymidine uptake measurements. The results showed a clear stimulation of the primary productivity as well as elevated amounts of chlorophyll a in the area receiving the effluent. Both bacterial abundances and production were an order of magnitude higher in a small area close to the refinery outlet, but dropped rapidly and reached background values outside an impacted area of c 10 km2. The increased bacterial production in this area corresponded to a substrate demand of 4 to 11 tonnes of carbon per day, 4 to 12 times the daily discharge of some 0·9 tonnes of carbon in the form of petroleum hydrocarbons from the oil refinery. These data, plus the low petroleum hydrocarbon concentrations found in the sediments and in bivalves outside the impacted area, suggest that bacterial degradation of the petroleum hydrocarbons from the refinery could be a major process restricting the area impacted by oil pollution. 

  • 50.
    Leitet, Cecilia
    et al.
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Riemann, Lasse
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Hagström, Åke
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Plasmids and Prophages in Baltic Sea Bacterioplankton.2006In: Journal of the Marine Biological Association of the United Kingdom, ISSN 1469-7769, Vol. 86, p. 567-575Article in journal (Refereed)
12 1 - 50 of 90
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