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Bunse, Carina
Publications (10 of 12) Show all publications
Nilsson, E., Li, K., Fridlund, J., Sulcius, S., Bunse, C., Karlsson, C. M. G., . . . Holmfeldt, K. (2019). Genomic and Seasonal Variations among Aquatic Phages Infecting the Baltic Sea Gammaproteobacterium Rheinheimera sp. Strain BAL341. Applied and Environmental Microbiology, 85(18), 1-19, Article ID e01003-19.
Open this publication in new window or tab >>Genomic and Seasonal Variations among Aquatic Phages Infecting the Baltic Sea Gammaproteobacterium Rheinheimera sp. Strain BAL341
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2019 (English)In: Applied and Environmental Microbiology, ISSN 0099-2240, E-ISSN 1098-5336, Vol. 85, no 18, p. 1-19, article id e01003-19Article in journal (Refereed) Published
Abstract [en]

Knowledge in aquatic virology has been greatly improved by culture-independent methods, yet there is still a critical need for isolating novel phages to identify the large proportion of "unknowns" that dominate metagenomes and for detailed analyses of phage-host interactions. Here, 54 phages infecting Rheinheimem sp. strain BAL341 (Gammaproteobacteria) were isolated from Baltic Sea seawater and characterized through genome content analysis and comparative genomics. The phages showed a myovirus-like morphology and belonged to a novel genus, for which we propose the name Barbavirus. All phages had similar genome sizes and numbers of genes (80 to 84 kb; 134 to 145 genes), and based on average nucleotide identity and genome BLAST distance phylogeny, the phages were divided into five species. The phages possessed several genes involved in metabolic processes and host signaling, such as genes encoding ribonucleotide reductase and thymidylate synthase, phoH, and rnazG. One species had additional metabolic genes involved in pyridine nucleotide salvage, possibly providing a fitness advantage by further increasing the phages' replication efficiency. Recruitment of viral metagenomic reads (25 Baltic Sea viral metagenomes from 2012 to 2015) to the phage genomes showed pronounced seasonal variations, with increased relative abundances of barba phages in August and September synchronized with peaks in host abundances, as shown by 16S rRNA gene amplicon sequencing. Overall, this study provides detailed information regarding genetic diversity, phage-host interactions, and temporal dynamics of an ecologically important aquatic phage-host system. IMPORTANCE Phages are important in aquatic ecosystems as they influence their microbial hosts through lysis, gene transfer, transcriptional regulation, and expression of phage metabolic genes. Still, there is limited knowledge of how phages interact with their hosts, especially at fine scales. Here, a Rheinheimera phage-host system constituting highly similar phages infecting one host strain is presented. This relatively limited diversity has previously been seen only when smaller numbers of phages have been isolated and points toward ecological constraints affecting the Rheinheimera phage diversity. The variation of metabolic genes among the species points toward various fitness advantages, opening up possibilities for future hypothesis testing. Phage-host dynamics monitored over several years point toward recurring "kill-the-winner" oscillations and an ecological niche fulfilled by this system in the Baltic Sea. Identifying and quantifying ecological dynamics of such phage-host model systems in situ allow us to understand and study the influence of phages on aquatic ecosystems.

Place, publisher, year, edition, pages
American Society for Microbiology, 2019
Keywords
Baltic Sea, bacteriophage, genomics, temporal variation
National Category
Ecology Microbiology
Research subject
Ecology, Microbiology; Ecology, Aquatic Ecology
Identifiers
urn:nbn:se:lnu:diva-89282 (URN)10.1128/AEM.01003-19 (DOI)000483596700008 ()31324626 (PubMedID)
Available from: 2019-09-25 Created: 2019-09-25 Last updated: 2019-10-01Bibliographically approved
Bunse, C., Israelsson, S., Baltar, F., Bertos-Fortis, M., Fridolfsson, E., Legrand, C., . . . Pinhassi, J. (2019). High Frequency Multi-Year Variability in Baltic Sea Microbial Plankton Stocks and Activities. Frontiers in Microbiology, 9, Article ID 3296.
Open this publication in new window or tab >>High Frequency Multi-Year Variability in Baltic Sea Microbial Plankton Stocks and Activities
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2019 (English)In: Frontiers in Microbiology, ISSN 1664-302X, E-ISSN 1664-302X, Vol. 9, article id 3296Article in journal (Refereed) Published
Abstract [en]

Marine bacterioplankton are essential in global nutrient cycling and organic matter turnover. Time-series analyses, often at monthly sampling frequencies, have established the paramount role of abiotic and biotic variables in structuring bacterioplankton communities and productivities. However, fine-scale seasonal microbial activities, and underlying biological principles, are not fully understood. We report results from four consecutive years of high-frequency time-series sampling in the Baltic Proper. Pronounced temporal dynamics in most investigated microbial variables were observed, including bacterial heterotrophic production, plankton biomass, extracellular enzyme activities, substrate uptake rate constants of glucose, pyruvate, acetate, amino acids, and leucine, as well as nutrient limitation bioassays. Spring blooms consisting of diatoms and dinoflagellates were followed by elevated bacterial heterotrophic production and abundances. During summer, bacterial productivity estimates increased even further, coinciding with an initial cyanobacterial bloom in early July. However, bacterial abundances only increased following a second cyanobacterial bloom, peaking in August. Uptake rate constants for the different measured carbon compounds varied seasonally and inter-annually and were highly correlated to bacterial productivity estimates, temperature, and cyanobacterial abundances. Further, we detected nutrient limitation in response to environmental conditions in a multitude of microbial variables, such as elevated productivities in nutrient bioassays, changes in enzymatic activities, or substrate preferences. Variations among biotic variables often occurred on time scales of days to a few weeks, yet often spanning several sampling occasions. Such dynamics might not have been captured by sampling at monthly intervals, as compared to more predictable transitions in abiotic variables such as temperature or nutrient concentrations. Our study indicates that high resolution analyses of microbial biomass and productivity parameters can help out in the development of biogeochemical and food web models disentangling the microbial black box.

Place, publisher, year, edition, pages
Frontiers Media S.A., 2019
Keywords
marine bacteria, phytoplankton, cyanobacteria, production, substrate uptake, enzyme activity, biogeochemistry
National Category
Microbiology Ecology
Research subject
Ecology, Microbiology; Ecology, Microbiology
Identifiers
urn:nbn:se:lnu:diva-80150 (URN)10.3389/fmicb.2018.03296 (DOI)000455948100001 ()2-s2.0-85064405301 (Scopus ID)
Available from: 2019-02-05 Created: 2019-02-05 Last updated: 2019-08-29Bibliographically approved
Fridolfsson, E., Bunse, C., Legrand, C., Lindehoff, E., Majaneva, S. & Hylander, S. (2019). Seasonal variation and species-specific concentrations of the essential vitamin B₁ (thiamin) in zooplankton and seston. Marine Biology, 166(6), 1-13, Article ID 70.
Open this publication in new window or tab >>Seasonal variation and species-specific concentrations of the essential vitamin B₁ (thiamin) in zooplankton and seston
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2019 (English)In: Marine Biology, ISSN 0025-3162, E-ISSN 1432-1793, Vol. 166, no 6, p. 1-13, article id 70Article in journal (Refereed) Published
Abstract [en]

Thiamin (vitamin B1) is mainly produced by bacteria and phytoplankton and then transferred to zooplankton and higher trophic levels but knowledge on the dynamics of these processes in aquatic ecosystems is lacking. Hence, the seasonal variation in thiamin content was assessed in field samples of copepods and in pico-, nano- and micro-plankton of two size classes (0.7–3 µm and > 3 µm) collected monthly in the Baltic Sea during 3 years and in the Skagerrak during 1 year. Copepods exhibited species-specific concentrations of thiamin and Acartia sp. had the highest carbon-specific thiamin content, at both locations. Even members of the same genus, but from different systems contained different levels of thiamin, with higher thiamin content per specimen in copepods from the Skagerrak compared to congeners from the Baltic Sea. Furthermore, our results show that the small plankton (0.7–3 µm) had a higher carbon-specific thiamin content compared to the large (> 3 µm). Additionally, there was a large seasonal variation and thiamin content was highly correlated comparing the two size fractions. Finally, there was an overall positive correlation between thiamin content in copepods and plankton. However, for periods of high thiamin content in the two size fractions, this correlation was negative. This suggests a decoupling between thiamin availability in pico-, nano- and micro-plankton and zooplankton in the Baltic Sea. Knowledge about concentrations of this essential micronutrient in the aquatic food web is limited and this study constitutes a foundation for further understanding the dynamics of thiamin in aquatic environments.

Place, publisher, year, edition, pages
New York, NY: Springer, 2019
National Category
Ecology
Research subject
Ecology, Aquatic Ecology
Identifiers
urn:nbn:se:lnu:diva-82081 (URN)10.1007/s00227-019-3520-6 (DOI)000467561000005 ()2-s2.0-85065572171 (Scopus ID)
Available from: 2019-04-23 Created: 2019-04-23 Last updated: 2019-11-15Bibliographically approved
Bunse, C. (2017). Bacterioplankton in the light of seasonality and environmental drivers. (Doctoral dissertation). Växjö: Linnaeus University Press
Open this publication in new window or tab >>Bacterioplankton in the light of seasonality and environmental drivers
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Bacterioplankton are keystone organisms in marine ecosystems. They are important for element cycles, by transforming dissolved organic carbon and other nutrients. Bacterioplankton community composition and productivity rates change in surface waters over spatial and temporal scales. Yet, many underlying biological processes determining when, why and how bacterioplankton react to changes in environmental conditions are poorly understood. Here, I used experiments with model bacteria and natural assemblages as well as field studies to determine molecular, physiological and ecological responses allowing marine bacteria to adapt to their environment.

Experiments with the flavobacterium Dokdonia sp. MED134 aimed to determine how the metabolism of bacteria is influenced by light and different organic matter. Under light exposure, Dokdonia sp. MED134 expressed proteorhodopsin and adjusted its metabolism to use resources more efficiently when growing with lower-quality organic matter. Similar expression patterns were found in oceanic datasets, implying a global importance of photoheterotrophic metabolisms for the ecology of bacterioplankton.

Further, I investigated how the composition and physiology of bacterial assemblages are affected by elevated CO2 concentrations and inorganic nutrients. In a large-scale experiment, bacterioplankton could keep productivity and community structure unaltered by adapting the gene expression under CO2 stress. To maintain pH homeostasis, bacteria induced higher expression of genes related to respiration, membrane transport and light acquisition under low-nutrient conditions. Under high-nutrient conditions with phytoplankton blooms, such regulatory mechanisms were not necessary. These findings indicate that open ocean systems are more vulnerable to ocean acidification than coastal waters.

Lastly, I used field studies to resolve how bacterioplankton is influenced by environmental changes, and how this leads to seasonal succession of marine bacteria. Using high frequency sampling over three years, we uncovered notable variability both between and within years in several biological features that rapidly changed over short time scales. These included potential phytoplankton-bacteria linkages, substrate uptake rates, and shifts in bacterial community structure. Thus, high resolution time series can provide important insights into the mechanisms controlling microbial communities.

Overall, this thesis highlights the advantages of combining molecular and traditional oceanographic methodological approaches to study ecosystems at high resolution for improving our understanding of the physiology and ecology of microbial communities and, ultimately, how they influence biogeochemical processes.

Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2017. p. 62
Series
Linnaeus University Dissertations ; 303/2017
Keywords
marine bacteria, marine microbiology, seasonal succession, ocean acidification, proteorhodopsin, photoheterotrophy, microbial time series
National Category
Environmental Sciences Oceanography, Hydrology and Water Resources Microbiology
Research subject
Ecology, Aquatic Ecology; Ecology, Microbiology; Natural Science, Environmental Science
Identifiers
urn:nbn:se:lnu:diva-69130 (URN)978-91-88761-03-3 (ISBN)978-91-88761-02-6 (ISBN)
Public defence
2018-01-12, Fullriggaren, Sjöfartshögskolan, Kalmar, 09:30 (English)
Supervisors
Funder
Ecosystem dynamics in the Baltic Sea in a changing climate perspective - ECOCHANGESwedish Research Council
Available from: 2017-12-11 Created: 2017-12-11 Last updated: 2018-02-21Bibliographically approved
Bunse, C. & Pinhassi, J. (2017). Marine bacterioplankton seasonal succession dynamics. Trends in Microbiology, 25(6), 495-505
Open this publication in new window or tab >>Marine bacterioplankton seasonal succession dynamics
2017 (English)In: Trends in Microbiology, ISSN 0966-842X, E-ISSN 1878-4380, Vol. 25, no 6, p. 495-505Article in journal (Refereed) Published
Abstract [en]

Bacterioplankton (bacteria and archaea) are indispensable regulators of global element cycles owing to their unique ability to decompose and remineralize dissolved organic matter. These microorganisms in surface waters worldwide exhibit pronounced seasonal succession patterns, governed by physicochemical factors (e.g., light, climate, and nutrient loading) that are determined by latitude and distance to shore. Moreover, we emphasize that the effects of large-scale factors are modulated regionally, and over shorter timespans (days to weeks), by biological interactions including molecule exchanges, viral lysis, and grazing. Thus the interplay and scaling between factors ultimately determine the success of particular bacterial populations. Spatiotemporal surveys of bacterioplankton community composition provide the necessary frame for interpreting how the distinct metabolisms encoded in the genomes of different bacteria regulate biogeochemical cycles.

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Biological Sciences
Research subject
Ecology, Microbiology
Identifiers
urn:nbn:se:lnu:diva-60291 (URN)10.1016/j.tim.2016.12.013 (DOI)000401231800011 ()28108182 (PubMedID)2-s2.0-85009761278 (Scopus ID)
Projects
EcoChange
Available from: 2017-01-27 Created: 2017-01-27 Last updated: 2019-08-29Bibliographically approved
Godhe, A., Sjoekvist, C., Sildever, S., Sefbom, J., Harðardóttir, S., Bertos-Fortis, M., . . . Rengefors, K. E. (2016). Physical barriers and environmental gradients cause spatial and temporal genetic differentiation of an extensive algal bloom. Journal of Biogeography, 43(6), 1130-1142
Open this publication in new window or tab >>Physical barriers and environmental gradients cause spatial and temporal genetic differentiation of an extensive algal bloom
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2016 (English)In: Journal of Biogeography, ISSN 0305-0270, E-ISSN 1365-2699, Vol. 43, no 6, p. 1130-1142Article in journal (Refereed) Published
Abstract [en]

Aim

To test if a phytoplankton bloom is panmictic, or whether geographical and environmental factors cause spatial and temporal genetic structure.

Location

Baltic Sea.

Method

During four cruises, we isolated clonal strains of the diatom Skeletonema marinoifrom 9 to 10 stations along a 1132 km transect and analysed the genetic structure using eight microsatellites. Using F-statistics and Bayesian clustering analysis we determined if samples were significantly differentiated. A seascape approach was applied to examine correlations between gene flow and oceanographic connectivity, and combined partial Mantel test and RDA based variation partitioning to investigate associations with environmental gradients.

Results

The bloom was initiated during the second half of March in the southern and the northern- parts of the transect, and later propagated offshore. By mid-April the bloom declined in the south, whereas high phytoplankton biomass was recorded northward. We found two significantly differentiated populations along the transect. Genotypes were significantly isolated by distance and by the south–north salinity gradient, which illustrated that the effects of distance and environment were confounded. The gene flow among the sampled stations was significantly correlated with oceanographic connectivity. The depletion of silica during the progression of the bloom was related to a temporal population genetic shift.

Main conclusions

A phytoplankton bloom may propagate as a continuous cascade and yet be genetically structured over both spatial and temporal scales. The Baltic Sea spring bloom displayed strong spatial structure driven by oceanographic connectivity and geographical distance, which was enhanced by the pronounced salinity gradient. Temporal transition of conditions important for growth may induce genetic shifts and different phenotypic strategies, which serve to maintain the bloom over longer periods.

Place, publisher, year, edition, pages
John Wiley & Sons, 2016
Keywords
Adaptation, Environmental gradient, Gene flow, Genetic structure, Isolation by distance, Population, Seascape, Skeletonema
National Category
Ecology
Research subject
Ecology, Aquatic Ecology
Identifiers
urn:nbn:se:lnu:diva-49736 (URN)10.1111/jbi.12722 (DOI)000378711000006 ()2-s2.0-84957818454 (Scopus ID)
Projects
EcoChange
Available from: 2016-02-15 Created: 2016-02-12 Last updated: 2018-06-08Bibliographically approved
Bunse, C., Lundin, D., Karlsson, C. M. G., Akram, N., Vila-Costa, M., Palovaara, J., . . . Pinhassi, J. (2016). Response of marine bacterioplankton pH homeostasis gene expression to elevated CO2. Nature Climate Change, 6(5), 483-487
Open this publication in new window or tab >>Response of marine bacterioplankton pH homeostasis gene expression to elevated CO2
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2016 (English)In: Nature Climate Change, ISSN 1758-678X, E-ISSN 1758-6798, Vol. 6, no 5, p. 483-487Article in journal (Refereed) Published
Abstract [en]

Human-induced ocean acidification impacts marine life. Marine bacteria are major drivers of biogeochemical nutrient cycles and energy fluxes1; hence, understanding their performance under projected climate change scenarios is crucial for assessing ecosystem functioning. Whereas genetic and physiological responses of phytoplankton to ocean acidification are being disentangled2, 3, 4, corresponding functional responses of bacterioplankton to pH reduction from elevated CO2 are essentially unknown. Here we show, from metatranscriptome analyses of a phytoplankton bloom mesocosm experiment, that marine bacteria responded to lowered pH by enhancing the expression of genes encoding proton pumps, such as respiration complexes, proteorhodopsin and membrane transporters. Moreover, taxonomic transcript analysis showed that distinct bacterial groups expressed different pH homeostasis genes in response to elevated CO2. These responses were substantial for numerous pH homeostasis genes under low-chlorophyll conditions (chlorophyll a <2.5 μg l−1); however, the changes in gene expression under high-chlorophyll conditions (chlorophyll a >20 μg l−1) were low. Given that proton expulsion through pH homeostasis mechanisms is energetically costly, these findings suggest that bacterioplankton adaptation to ocean acidification could have long-term effects on the economy of ocean ecosystems.

National Category
Microbiology Ecology Climate Research
Research subject
Ecology, Microbiology
Identifiers
urn:nbn:se:lnu:diva-49969 (URN)10.1038/nclimate2914 (DOI)000375125200015 ()2-s2.0-84964949342 (Scopus ID)
Projects
EcoChange
Available from: 2016-02-29 Created: 2016-02-29 Last updated: 2018-10-24Bibliographically approved
Bunse, C., Bertos-Fortis, M., Sassenhagen, I., Sildever, S., Sjöqvist, C., Godhe, A., . . . Legrand, C. (2016). Spatio-Temporal Interdependence of Bacteria and Phytoplankton during a Baltic Sea Spring Bloom. Frontiers in Microbiology, 7, Article ID 517.
Open this publication in new window or tab >>Spatio-Temporal Interdependence of Bacteria and Phytoplankton during a Baltic Sea Spring Bloom
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2016 (English)In: Frontiers in Microbiology, ISSN 1664-302X, E-ISSN 1664-302X, Vol. 7, article id 517Article in journal (Refereed) Published
Abstract [en]

In temperate systems, phytoplankton spring blooms deplete inorganic nutrients and are major sources of organic matter for the microbial loop. In response to phytoplankton exudates and environmental factors, heterotrophic microbial communities are highly dynamic and change their abundance and composition both on spatial and temporal scales. Yet, most of our understanding about these processes comes from laboratory model organism studies, mesocosm experiments or single temporal transects. Spatial -temporal studies examining interactions of phytoplankton blooms and bacterioplankton community composition and function, though being highly informative, are scarce. In this study, pelagic microbial community dynamics (bacteria and phytoplankton) and environmental variables were monitored during a spring bloom across the Baltic Proper (two cruises between North Germany to Gulf of Finland). To test to what extent bacterioplankton community composition relates to the spring bloom, we used next generation amplicon sequencing of the 16S rRNA gene, phytoplankton diversity analysis based on microscopy counts and population genotyping of the dominating diatom Skeletonema rnarinoi. Several phytoplankton bloom related and environmental variables were identified to influence bacterial community composition. Members of Bacteroidetes and Alphaproteobacteria dominated the bacterial community composition but the bacterial groups showed no apparent correlation with direct bloom related variables. The less abundant bacterial phyla Actinobacteria, Planctomycetes, and Verrucomicrobia, on the other hand, were strongly associated with phytoplankton biomass, diatom:dinoflagellate ratio, and colored dissolved organic matter (cDOM). Many bacterial operational taxonomic units (OTUs) showed high niche specificities. For example, particular Bacteroidetes OTUs were associated with two distinct genetic clusters of S. marinoi. Our study revealed the complexity of interactions of bacterial taxa with inter- and intraspecific genetic variation in phytoplankton. Overall, our findings imply that biotic and abiotic factors during spring bloom influence bacterial community dynamics in a hierarchical manner.

Place, publisher, year, edition, pages
Frontiers Media S.A., 2016
Keywords
16S rRNA, marine bacteria, bacterioplankton, phytoplankton, Skeletonema marinoi, spring bloom, Baltic Sea, spatio-temporal
National Category
Ecology Microbiology
Research subject
Ecology, Aquatic Ecology
Identifiers
urn:nbn:se:lnu:diva-53313 (URN)10.3389/fmicb.2016.00517 (DOI)000374468900001 ()2-s2.0-84966263551 (Scopus ID)
Projects
Ecochange
Available from: 2016-06-10 Created: 2016-06-10 Last updated: 2018-10-24Bibliographically approved
Bunse, C. (2015). Bacterioplankton community associated with the Baltic Sea spring bloom. (Student paper). Linnéuniversitetet
Open this publication in new window or tab >>Bacterioplankton community associated with the Baltic Sea spring bloom
2015 (English)Student thesis
Abstract [en]

Marine microbial communities are highly dynamic, respond to environmental drivers and change on spatial and temporal scales. In the Baltic Sea, recent surveys show that the salinity gradient structures bacterioplankton community composition. Yet, these surveys were conducted during summer when environmental conditions were relatively stable. The spring bloom is initiated by near-zero temperatures, depletes inorganic nutrients and is the major source of organic matter in the system. In this study, bacterioplankton dynamics, phytoplankton and environmental parameters were monitored during the transition of the spring bloom on transects across the Baltic Proper, from Finland to Germany. Using next generation amplicon sequencing of the 16S rRNA gene, we studied the bacterial community composition during the general transition of the plankton community from new to regenerated production. We show that on short temporal scales, the microbial community composition varies across large spatial scales. Gammaproteobacteria and Betaproteobacteria were highly abundant in the open Baltic Proper, and were strongly correlated to phosphate availability during early stages of the spring bloom. During the mature bloom stage, the bacterioplankton communities was highly similar along the entire transect, dominated by Bacteroidetes, Actinobacteria and Alphaproteobacteria. Compared to other surveys we found that salinity is not solely driving the Baltic Sea bacterioplankton community composition during spring bloom conditions. Thus, changes in nutrient availability, timing and transition of the bloom can act as selective forces, structuring microbial communities.

Keywords
16S rRNA amplicon sequencing, diatom spring bloom, marine bacteria
National Category
Natural Sciences
Identifiers
urn:nbn:se:lnu:diva-42932 (URN)
Thesis level
Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE credits
Presentation
2015-04-27, A137, 13:00 (English)
Supervisors
Examiners
Available from: 2018-01-30 Created: 2015-04-30 Last updated: 2018-01-30Bibliographically approved
Palovaara, J., Akram, N., Baltar, F., Bunse, C., Forsberg, J., Pedrós-Alió, C., . . . Pinhassi, J. (2014). Stimulation of growth by proteorhodopsin phototrophy involves regulation of central metabolic pathways in marine planktonic bacteria. Proceedings of the National Academy of Sciences of the United States of America, 111(35), E3650-E3658
Open this publication in new window or tab >>Stimulation of growth by proteorhodopsin phototrophy involves regulation of central metabolic pathways in marine planktonic bacteria
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2014 (English)In: Proceedings of the National Academy of Sciences of the United States of America, ISSN 0027-8424, E-ISSN 1091-6490, Vol. 111, no 35, p. E3650-E3658Article in journal (Refereed) Published
Abstract [en]

Proteorhodopsin (PR) is present in half of surface ocean bacterioplankton, where its light-driven proton pumping provides energy to cells. Indeed, PR promotes growth or survival in different bacteria. However, the metabolic pathways mediating the light responses remain unknown. We analyzed growth of the PR-containing Dokdonia sp. MED134 (where light-stimulated growth had been found) in seawater with low concentrations of mixed [yeast extract and peptone (YEP)] or single (alanine, Ala) carbon compounds as models for rich and poor environments. We discovered changes in gene expression revealing a tightly regulated shift in central metabolic pathways between light and dark conditions. Bacteria showed relatively stronger light responses in Ala compared with YEP. Notably, carbon acquisition pathways shifted toward anaplerotic CO2 fixation in the light, contributing 31 +/- 8% and 24 +/- 6% of the carbon incorporated into biomass in Ala and YEP, respectively. Thus, MED134 was a facultative double mixotroph, i.e., photo- and chemotrophic for its energy source and using both bicarbonate and organic matter as carbon sources. Unexpectedly, relative expression of the glyoxylate shunt genes (isocitrate lyase and malate synthase) was >300-fold higher in the light-but only in Ala-contributing a more efficient use of carbon from organic compounds. We explored these findings in metagenomes and metatranscriptomes and observed similar prevalence of the glyoxylate shunt compared with PR genes and highest expression of the isocitrate lyase gene coinciding with highest solar irradiance. Thus, regulatory interactions between dissolved organic carbon quality and central metabolic pathways critically determine the fitness of surface ocean bacteria engaging in PR phototrophy.

National Category
Ecology
Research subject
Natural Science, Aquatic Ecology
Identifiers
urn:nbn:se:lnu:diva-37306 (URN)10.1073/pnas.1402617111 (DOI)000341230800012 ()2-s2.0-84907227908 (Scopus ID)
Available from: 2014-09-27 Created: 2014-09-27 Last updated: 2017-12-11Bibliographically approved
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