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Riemann, Lasse
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Publications (10 of 47) Show all publications
Rowe, O. F., Dinasquet, J., Paczkowska, J., Figueroa, D., Riemann, L. & Andersson, A. (2018). Major differences in dissolved organic matter characteristics and bacterial processing over an extensive brackish water gradient, the Baltic Sea. Marine Chemistry, 202, 27-36
Open this publication in new window or tab >>Major differences in dissolved organic matter characteristics and bacterial processing over an extensive brackish water gradient, the Baltic Sea
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2018 (English)In: Marine Chemistry, ISSN 0304-4203, E-ISSN 1872-7581, Vol. 202, p. 27-36Article in journal (Refereed) Published
Abstract [en]

Dissolved organic matter (DOM) in marine waters is a complex mixture of compounds and elements that contribute substantially to the global carbon cycle. The large reservoir of dissolved organic carbon (DOC) represents a vital resource for heterotrophic bacteria. Bacteria can utilise, produce, recycle and transform components of the DOM pool, and the physicochemical characteristics of this pool can directly influence bacterial activity; with consequences for nutrient cycling and primary productivity. In the present study we explored bacterial transformation of naturally occurring DOM across an extensive brackish water gradient in the Baltic Sea. Highest DOC utilisation (indicated by decreased DOC concentration) was recorded in the more saline southerly region where waters are characterised by more autochthonous DOM. These sites expressed the lowest bacterial growth efficiency (BGE), whereas in northerly regions, characterised by higher terrestrial and allochthonous DOM, the DOC utilisation was low and BGE was highest. Bacterial processing of the DOM pool in the south resulted in larger molecular weight compounds and compounds associated with secondary terrestrial humic matter being degraded, and a processed DOM pool that was more aromatic in nature and contributed more strongly to water colour; while the opposite was true in the north. Nutrient concentration and stoichiometry and DOM characteristics affected bacterial activity, including metabolic status (BGE), which influenced DOM transformations. Our study highlights dramatic differences in DOM characteristics and microbial carbon cycling in sub-basins of the Baltic Sea. These findings are critical for our understanding of carbon and nutrient biogeochemistry, particularly in light of climate change scenarios.

Place, publisher, year, edition, pages
Elsevier, 2018
Keywords
Dissolved organic matter, DOC utilisation, DOM fluorescence, Bacterial growth efficiency, Bacterial production, Baltic Sea
National Category
Biological Sciences
Research subject
Ecology, Aquatic Ecology
Identifiers
urn:nbn:se:lnu:diva-76847 (URN)10.1016/j.marchem.2018.01.010 (DOI)000432764600003 ()
Available from: 2018-07-13 Created: 2018-07-13 Last updated: 2018-07-13Bibliographically approved
Farnelid, H., Harder, J., Bentzon-Tilia, M. & Riemann, L. (2014). Isolation of heterotrophic diazotrophic bacteria from estuarine surface waters. Environmental Microbiology, 16(10), 3072-3082
Open this publication in new window or tab >>Isolation of heterotrophic diazotrophic bacteria from estuarine surface waters
2014 (English)In: Environmental Microbiology, ISSN 1462-2912, E-ISSN 1462-2920, Vol. 16, no 10, p. 3072-3082Article in journal (Refereed) Published
Abstract [en]

The wide distribution of diverse nitrogenase (nifH) genes affiliated with those of heterotrophic bacteria in marine and estuarine waters indicates ubiquity and an ecologically relevant role for heterotrophic N-2-fixers (diazotrophs) in aquatic nitrogen (N) cycling. However, the lack of cultivated representatives currently precludes an evaluation of their N-2-fixing capacity. In this study, microoxic or anoxic N-free media were inoculated with estuarine Baltic Sea surface water to select for N-2-fixers. After visible growth and isolation of single colonies on oxic plates or in anoxic agar tubes, nifH gene amplicons were obtained from 64 strains and nitrogenase activity, applying the acetylene reduction assay, was confirmed for 40 strains. Two strains, one Gammaproteobacterium affiliated with Pseudomonas and one Alphaproteobacterium affiliated with Rhodopseudomonas were shown to represent established members of the indigenous diazotrophic community in the Baltic Sea, with abundances of up to 7.9x10(4) and 4.7x10(4)nifH copies l(-1) respectively. This study reports media for successful isolation of heterotrophic diazotrophs. The applied methodology and the obtained strains will facilitate future identification of factors controlling heterotrophic diazotrophic activity in aquatic environments, which is a prerequisite for understanding and evaluating their ecology and contribution to N cycling at local and regional scales.

National Category
Microbiology
Research subject
Natural Science, Microbiology
Identifiers
urn:nbn:se:lnu:diva-38488 (URN)10.1111/1462-2920.12335 (DOI)000343867700006 ()2-s2.0-84907877905 (Scopus ID)
Available from: 2014-12-03 Created: 2014-12-03 Last updated: 2017-12-05Bibliographically approved
Farnelid, H., Bentzon-Tilia, M., Andersson, A. F., Bertilsson, S., Jost, G., Labrenz, M., . . . Riemann, L. (2013). Active nitrogen-fixing heterotrophic bacteria at and below the chemocline of the central Baltic Sea. The ISME Journal, 7(7), 1413-1423
Open this publication in new window or tab >>Active nitrogen-fixing heterotrophic bacteria at and below the chemocline of the central Baltic Sea
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2013 (English)In: The ISME Journal, ISSN 1751-7362, E-ISSN 1751-7370, Vol. 7, no 7, p. 1413-1423Article in journal (Refereed) Published
Abstract [en]

The Baltic Sea receives large nitrogen inputs by diazotrophic (N-2-fixing) heterocystous cyanobacteria but the significance of heterotrophic N-2 fixation has not been studied. Here, the diversity, abundance and transcription of the nifH fragment of the nitrogenase enzyme in two basins of the Baltic Sea proper was examined. N-2 fixation was measured at the surface (5 m) and in anoxic water (200 m). Vertical sampling profiles of >10 and <10 mu m size fractions were collected in 2007, 2008 and 2011 at the Gotland Deep and in 2011 in the Bornholm Basin. Both of these stations are characterized by permanently anoxic bottom water. The 454-pyrosequencing nifH analysis revealed a diverse assemblage of nifH genes related to alpha-, beta- and gammaproteobacteria (nifH cluster I) and anaerobic bacteria (nifH cluster III) at and below the chemocline. Abundances of genes and transcripts of seven diazotrophic phylotypes were investigated using quantitative polymerase chain reaction revealing abundances of heterotrophic nifH phylotypes of up to 2.1 x 10(7) nifH copies l(-1). Abundant nifH transcripts (up to 3.2 x 10(4) transcripts l(-1)) within nifH cluster III and co-occurring N-2 fixation (0.44 +/- 0.26 nmol l(-1) day(-1)) in deep water suggests that heterotrophic diazotrophs are fixing N2 in anoxic ammonium-rich waters. Our results reveal that N-2 fixation in the Baltic Sea is not limited to illuminated N-deplete surface waters and suggest that N-2 fixation could also be of importance in other suboxic regions of the world's oceans.

Keywords
Baltic Sea, chemocline, nifH, nitrogen fixation, oxic-anoxic interface, pyrosequencing
National Category
Ecology
Research subject
Natural Science, Aquatic Ecology
Identifiers
urn:nbn:se:lnu:diva-28361 (URN)10.1038/ismej.2013.26 (DOI)000320852100016 ()2-s2.0-84880919938 (Scopus ID)
Available from: 2013-08-22 Created: 2013-08-22 Last updated: 2017-12-06Bibliographically approved
Lindh, M. V., Riemann, L., Baltar, F., Romero-Oliva, C., Salomon, P., Granéli, E. & Pinhassi, J. (2013). Consequences of increased temperature and acidification on bacterioplankton community composition during a mesocosm spring bloom in the Baltic Sea. Environmental Microbiology Reports, 5(2), 252-262
Open this publication in new window or tab >>Consequences of increased temperature and acidification on bacterioplankton community composition during a mesocosm spring bloom in the Baltic Sea
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2013 (English)In: Environmental Microbiology Reports, ISSN 1758-2229, E-ISSN 1758-2229, Vol. 5, no 2, p. 252-262Article in journal (Refereed) Published
Abstract [en]

Despite the paramount importance of bacteria for biogeochemical cycling of carbon and nutrients, little is known about the potential effects of climate change on these key organisms. The consequences of the projected climate change on bacterioplankton community dynamics were investigated in a Baltic Sea spring phytoplankton bloom mesocosm experiment by increasing temperature with 3°C and decreasing pH by approximately 0.4 units via CO2 addition in a factorial design. Temperature was the major driver of differences in community composition during the experiment, as shown by denaturing gradient gel electrophoresis (DGGE) of amplified 16S rRNA gene fragments. Several bacterial phylotypes belonging to Betaproteobacteria were predominant at 3°C but were replaced by members of the Bacteriodetes in the 6°C mesocosms. Acidification alone had a limited impact on phylogenetic composition, but when combined with increased temperature, resulted in the proliferation of specific microbial phylotypes. Our results suggest that although temperature is an important driver in structuring bacterioplankton composition, evaluation of the combined effects of temperature and acidification is necessary to fully understand consequences of climate change for marine bacterioplankton, their implications for future spring bloom dynamics, and their role in ecosystem functioning.

National Category
Ecology
Research subject
Ecology, Aquatic Ecology
Identifiers
urn:nbn:se:lnu:diva-22627 (URN)10.1111/1758-2229.12009 (DOI)000315851200008 ()23584969 (PubMedID)2-s2.0-84874716930 (Scopus ID)
Available from: 2012-11-27 Created: 2012-11-27 Last updated: 2019-01-23Bibliographically approved
Degerman, R., Dinasquet, J., Riemann, L., de Luna, S. S. & Andersson, A. (2013). Effect of resource availability on bacterial community responses to increased temperature. Aquatic Microbial Ecology, 68(2), 131-142
Open this publication in new window or tab >>Effect of resource availability on bacterial community responses to increased temperature
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2013 (English)In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 68, no 2, p. 131-142Article in journal (Refereed) Published
Abstract [en]

Climate change is predicted to cause higher temperatures and increased precipitation, resulting in increased inflow of nutrients to coastal waters in northern Europe. This has been assumed to increase the overall heterotrophy, including enhanced bacterial growth. However, the relative importance of temperature, resource availability and bacterial community composition for the bacterial growth response is poorly understood. In the present study, we investigated effects of increased temperature on bacterial growth in waters supplemented with different nutrient concentrations and inoculated with microbial communities from distinct seasonal periods. Seven experiments were performed in the northern Baltic Sea spanning an entire annual cycle. In each experiment, bacterioplankton were exposed to 2 temperature regimes (in situ and in situ + 4 degrees C) and 5 nutrient concentrations. Generally, elevated temperature and higher nutrient levels caused an increase in the bacterial growth rate and a shortening of the response time (lag phase). However, at the lowest nutrient concentration, bacterial growth was low at all tested temperatures, implying a stronger dependence on resource availability than on temperature for bacterial growth. Furthermore, data indicated that different bacterial assemblages had varying temperature responses and that community composition was strongly affected by the combination of high nutrient addition and high temperature. These results support the concern that climate change will promote heterotrophy in aquatic systems, where nutrient levels will increase considerably. In such environments, the bacterial community composition will change, their growth rates will increase, and their response time will be shortened compared to the present situation.

Keywords
Temperature increase, Resource availability, Bacterial growth response, Climate change, Community dynamics
National Category
Microbiology
Research subject
Natural Science, Microbiology
Identifiers
urn:nbn:se:lnu:diva-24863 (URN)10.3354/ame01609 (DOI)000315598900004 ()2-s2.0-84873908033 (Scopus ID)
Available from: 2013-03-22 Created: 2013-03-22 Last updated: 2017-12-06Bibliographically approved
Dinasquet, J., Kragh, T., Schroter, M.-L., Sondergaard, M. & Riemann, L. (2013). Functional and compositional succession of bacterioplankton in response to a gradient in bioavailable dissolved organic carbon. Environmental Microbiology, 15(9), 2616-2628
Open this publication in new window or tab >>Functional and compositional succession of bacterioplankton in response to a gradient in bioavailable dissolved organic carbon
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2013 (English)In: Environmental Microbiology, ISSN 1462-2912, E-ISSN 1462-2920, Vol. 15, no 9, p. 2616-2628Article in journal (Refereed) Published
Abstract [en]

Studies indicate that bacterial taxa utilize different fractions of the dissolved organic carbon (DOC) pool, while others suggest functional redundancy among constituents of bacterioplankton, implying only a weak coupling between community structure and function. We examined bacterial compositional and functional [ectoenzymatic activities and growth efficiency; bacterial growth efficiency (BGE)] responses to a gradient in bioavailable DOC (bDOC). This was achieved over 10 days in DOC utilization assays containing Baltic Sea water with variable amounts of natural bDOC. Measurements of bacterial growth, O-2 and DOC consumption in the assays using non-invasive sampling showed that BGE changed over time and that the bDOC utilized accounted for 4-13% of the DOC pool. Pyrosequencing of 16S rRNA genes demonstrated minor differences at the phylum level between samples, whereas larger successional differences were discernible at lower phylogenetic levels. Our study suggests that changes in concentrations of bDOC affect bacterioplankton BGE and community structure by selecting for some taxa while the relative abundance of most taxa remained unaffected. Ectoenzymes activities suggested preferential degradation of protein-rich compounds by bacteria, switching to carbohydrate-rich DOC when proteins were depleted. Hence, there was a fairly weak linkage between bacterial community composition and DOC utilization suggesting that overall bacterioplankton community structure only to some extent has predictive power for processing of the DOC pool.

National Category
Biological Sciences
Research subject
Natural Science, Cell and Organism Biology
Identifiers
urn:nbn:se:lnu:diva-29202 (URN)10.1111/1462-2920.12178 (DOI)000323897000016 ()2-s2.0-84883554524 (Scopus ID)
Available from: 2013-10-04 Created: 2013-10-03 Last updated: 2017-12-06Bibliographically approved
Sjöstedt, J., Pontarp, M., Tinta, T., Alfredsson, H., Turk, V., Lundberg, P., . . . Riemann, L. (2013). Reduced diversity and changed bacterioplankton community composition do not affect utilization of dissolved organic matter in the Adriatic Sea. Aquatic Microbial Ecology, 71(1), 15-U132
Open this publication in new window or tab >>Reduced diversity and changed bacterioplankton community composition do not affect utilization of dissolved organic matter in the Adriatic Sea
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2013 (English)In: Aquatic Microbial Ecology, ISSN 0948-3055, E-ISSN 1616-1564, Vol. 71, no 1, p. 15-U132Article in journal (Refereed) Published
Abstract [en]

To obtain insights into the coupling between community composition, diversity and community function, bacterioplankton assemblages from the Gulf of Trieste (Northern Adriatic Sea) were exposed to increasing environmental stress throughout 2 wk in continuous seawater cultures to construct communities differing in composition and diversity. The assemblages were exposed to (1) decreased temperature, (2) decreased temperature and phosphate addition or (3) decreased temperature, phosphate addition and lowered oxygen level. Bacterial and viral abundances as well as bacterial community composition stabilized during the second week of the experiment. Denaturing gradient gel electrophoresis and pyrosequencing of 16S rRNA genes showed dramatic reductions in bacterial diversity in all treatments and major compositional differences relative to the inoculum. Nevertheless, no differences in the ability to exploit dissolved organic carbon (DOC) were found for the acquired communities relative to the inoculum, indicating that the bacterial communities were functionally redundant. We speculate that oscillations in exploitation of the DOC pool in situ are mainly governed by factors limiting the overall bacterial growth, rather than perturbations affecting only subsets of the microbial biota.

Keywords
Diversity, Functional redundancy, Community structure, Continuous cultures, DOC
National Category
Ecology
Research subject
Natural Science, Aquatic Ecology
Identifiers
urn:nbn:se:lnu:diva-31322 (URN)10.3354/ame01660 (DOI)000327552900002 ()2-s2.0-84889049698 (Scopus ID)
Available from: 2013-12-19 Created: 2013-12-19 Last updated: 2019-02-27Bibliographically approved
Holmfeldt, K., Solonenko, N., Shah, M., Corrier, K., Riemann, L., VerBerkmoes, N. C. & Sullivan, M. B. (2013). Twelve previously unknown phage genera are ubiquitous in global oceans. Proceedings of the National Academy of Sciences of the United States of America, 110(31), 12798-12803
Open this publication in new window or tab >>Twelve previously unknown phage genera are ubiquitous in global oceans
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2013 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 110, no 31, p. 12798-12803Article in journal (Refereed) Published
Abstract [en]

Viruses are fundamental to ecosystems ranging from oceans to humans, yet our ability to study them is bottlenecked by the lack of ecologically relevant isolates, resulting in "unknowns" dominating culture-independent surveys. Here we present genomes from 31 phages infecting multiple strains of the aquatic bacterium Cellulophaga baltica (Bacteroidetes) to provide data for an under-represented and environmentally abundant bacterial lineage. Comparative genomics delineated 12 phage groups that (i) each represent a new genus, and (ii) represent one novel and four well-known viral families. This diversity contrasts the few well-studied marine phage systems, but parallels the diversity of phages infecting human-associated bacteria. Although all 12 Cellulophaga phages represent new genera, the podoviruses and icosahedral, nontailed ssDNA phages were exceptional, with genomes up to twice as large as those previously observed for each phage type. Structural novelty was also substantial, requiring experimental phage proteomics to identify 83% of the structural proteins. The presence of uncommon nucleotide metabolism genes in four genera likely underscores the importance of scavenging nutrient-rich molecules as previously seen for phages in marine environments. Metagenomic recruitment analyses suggest that these particular Cellulophaga phages are rare and may represent a first glimpse into the phage side of the rare biosphere. However, these analyses also revealed that these phage genera are widespread, occurring in 94% of 137 investigated metagenomes. Together, this diverse and novel collection of phages identifies a small but ubiquitous fraction of unknown marine viral diversity and provides numerous environmentally relevant phage-host systems for experimental hypothesis testing.

Keywords
model systems, phage genomics, phage taxonomy, queuosine biosynthesis, prophage
National Category
Microbiology
Research subject
Biomedical Sciences, Virology
Identifiers
urn:nbn:se:lnu:diva-29212 (URN)10.1073/pnas.1305956110 (DOI)000322441500068 ()
Available from: 2013-10-04 Created: 2013-10-03 Last updated: 2018-02-19Bibliographically approved
Holmfeldt, K., Odić, D., Sullivan, M. B., Middelboe, M. & Riemann, L. (2012). Cultivated single-stranded DNA phages that infect marine Bacteroidetes prove difficult to detect with DNA-binding stains.. Applied and Environmental Microbiology, 78(3), 892-894
Open this publication in new window or tab >>Cultivated single-stranded DNA phages that infect marine Bacteroidetes prove difficult to detect with DNA-binding stains.
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2012 (English)In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 78, no 3, p. 892-894Article in journal (Refereed) Published
Abstract [en]

This is the first description of cultivated icosahedral single-stranded DNA (ssDNA) phages isolated on heterotrophic marine bacterioplankton and with Bacteroidetes hosts. None of the 8 phages stained well with DNA-binding stains, suggesting that in situ abundances of ssDNA phages are drastically underestimated using conventional methods for enumeration.

National Category
Microbiology
Research subject
Natural Science, Microbiology
Identifiers
urn:nbn:se:lnu:diva-22847 (URN)10.1128/AEM.06580-11 (DOI)22138992 (PubMedID)2-s2.0-84856148335 (Scopus ID)
Available from: 2012-12-12 Created: 2012-12-12 Last updated: 2017-12-07Bibliographically approved
Sjöstedt, J., Koch-Schmidt, P., Pontarp, M., Canbäck, B., Tunlid, A., Lundberg, P., . . . Riemann, L. (2012). Recruitment of members from the rare biosphere of marine bacterioplankton communities after an environmental disturbance.. Applied and Environmental Microbiology, 78(5), 1361-1369
Open this publication in new window or tab >>Recruitment of members from the rare biosphere of marine bacterioplankton communities after an environmental disturbance.
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2012 (English)In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 78, no 5, p. 1361-1369Article in journal (Refereed) Published
Abstract [en]

A bacterial community may be resistant to environmental disturbances if some of its species show metabolic flexibility and physiological tolerance to the changing conditions. Alternatively, disturbances can change the composition of the community and thereby potentially affect ecosystem processes. The impact of disturbance on the composition of bacterioplankton communities was examined in continuous seawater cultures. Bacterial assemblages from geographically closely connected areas, the Baltic Sea (salinity 7 and high dissolved organic carbon [DOC]) and Skagerrak (salinity 28 and low DOC), were exposed to gradual opposing changes in salinity and DOC over a 3-week period such that the Baltic community was exposed to Skagerrak salinity and DOC and vice versa. Denaturing gradient gel electrophoresis and clone libraries of PCR-amplified 16S rRNA genes showed that the composition of the transplanted communities differed significantly from those held at constant salinity. Despite this, the growth yields (number of cells ml(-1)) were similar, which suggests similar levels of substrate utilization. Deep 454 pyrosequencing of 16S rRNA genes showed that the composition of the disturbed communities had changed due to the recruitment of phylotypes present in the rare biosphere of the original community. The study shows that members of the rare biosphere can become abundant in a bacterioplankton community after disturbance and that those bacteria can have important roles in maintaining ecosystem processes.

National Category
Microbiology
Research subject
Natural Science, Microbiology
Identifiers
urn:nbn:se:lnu:diva-22845 (URN)10.1128/AEM.05542-11 (DOI)22194288 (PubMedID)2-s2.0-84857065812 (Scopus ID)
Available from: 2012-12-14 Created: 2012-12-12 Last updated: 2019-02-27Bibliographically approved
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