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| 2. |
- Dupont, Chris L., et al.
(författare)
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Functional Tradeoffs Underpin Salinity-Driven Divergence in Microbial Community Composition
- 2014
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:2, s. e89549-
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
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| 4. |
- Hugerth, Luisa W., et al.
(författare)
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Systematic Design of 18S rRNA Gene Primers for Determining Eukaryotic Diversity in Microbial Consortia
- 2014
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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 9:4, s. 095567-
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Tidskriftsartikel (refereegranskat)abstract
- High-throughput sequencing of ribosomal RNA gene (rDNA) amplicons has opened up the door to large-scale comparative studies of microbial community structures. The short reads currently produced by massively parallel sequencing technologies make the choice of sequencing region crucial for accurate phylogenetic assignments. While for 16S rDNA, relevant regions have been well described, no truly systematic design of 18S rDNA primers aimed at resolving eukaryotic diversity has yet been reported. Here we used 31,862 18S rDNA sequences to design a set of broad-taxonomic range degenerate PCR primers. We simulated the phylogenetic information that each candidate primer pair would retrieve using paired-or single-end reads of various lengths, representing different sequencing technologies. Primer pairs targeting the V4 region performed best, allowing discrimination with paired-end reads as short as 150 bp (with 75% accuracy at genus level). The conditions for PCR amplification were optimised for one of these primer pairs and this was used to amplify 18S rDNA sequences from isolates as well as from a range of environmental samples which were then Illumina sequenced and analysed, revealing good concordance between expected and observed results. In summary, the reported primer sets will allow minimally biased assessment of eukaryotic diversity in different microbial ecosystems.
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| 5. |
- Karlsson, Christofer M. G., et al.
(författare)
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Different gene expression responses in two Baltic Sea heterotrophic model bacteria to dinoflagellate dissolved organic matter
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Phytoplankton release massive amounts of dissolved organic matter (DOM) into the water column during recurring blooms in coastal waters and inland seas. The released DOM includes dissolved organic carbon, nitrogen and phosphorus, in a complex mixture of both known and unknown compounds, and is a rich nutrient source for heterotrophic bacteria. The metabolic activity of heterotrophic bacteria during and after phytoplankton blooms can hence be expected to reflect the characteristics of the released DOM. With this in mind, we wanted to investigate if bacterioplankton could be used as “living sensors” of phytoplankton DOM quantity and quality, and to trace the flow of nutrients in the ecosystem. We used transcriptional activity from Baltic Sea bacterial isolates (Polaribacter sp. BAL334 (Flavobacteriia) and Brevundimonas sp. BAL450 (Alphaproteobacteria)) exposed to DOM derived from the dinoflagellate Prorocentrum minimum in exponential and stationary growth phases respectively. We observed strong responses both in terms of physiology – bacterial abundance – and the expressed metabolic pathways – e.g. Membrane Transport, Fatty Acids, Lipids and Isoprenoids – of the populations in samples exposed to dinoflagellate DOM compared with controls. Particularly striking was the increased expression of Ton and Tol transport systems, commonly associated with uptake of complex molecules, in both isolates. Equally important were the differences in metabolic responses between the two isolates, caused by differences in gene repertoire between them, emphasizing the importance of separating the responses of different taxa in analyses of community sequence data. Differences in response to DOM sourced from exponentially and stationary growing dinoflagellates were less pronounced, although not absent, than differences between the bacterial isolates. This suggests that shifts in metabolism during the different phases of a phytoplankton bloom might be detectable in individual bacterial populations. To conclude, our work opened a door to the future use of bacterioplankton as living sensors of environmental status, particularly with respect to phytoplankton blooms.
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| 6. |
- Karlsson, Christofer M. G., et al.
(författare)
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Metatranscriptomic analysis uncovers divergent responses of Baltic Sea bacteria to forest and agriculture river loadings
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Climate change is predicted to induce substantial changes in precipitation patterns across the globe. In Northern Europe, precipitation is expected to increase more than the global average (particularly in northern Scandinavia), causing increased river runoff. The Baltic Sea is one of the largest brackish environments on earth with a catchment area that spans 14 countries, encompassing primarily forested areas and agricultural landscapes. Despite the acknowledged role of marine bacteria in nutrient cycling, there is a lack of knowledge in their metabolic responses to inorganic and organic nutrient loading from riverine runoff. We investigated the bacterial growth and gene expression responses in a mesocosm experiment in which river water from boreal forest- (enriched in humic substances) or agriculture- influenced catchment areas were added to Baltic Sea Proper water. The riverine nutrient input triggered extensive phytoplankton blooms and bacterial growth, most notably in the agriculture river treatment. Interestingly, bacterial gene expression analysis (metatranscriptomics) showed similar responses to agriculture and humic river inputs at the start of the experiment (before the phytoplankton bloom), but expression patterns diverged significantly upon bloom senescence.Notably, transcripts associated with phosphate metabolism were significantly enriched , whereas transcripts related to nitrogen metabolism were significantly lower in the agriculture river treatment compared to the boreal forest river treatment. The opposite pattern was observed in the boreal forest river water treatment. Overall, our results showed that interactions between river nutrient loading and phytoplankton organic matter are important in regulating bacterial activities and responses at the molecular level. This suggests that bacterial transformations of organic matter and nutrient cycling in coastal waters and estuarine environments are sensitive to changes in precipitation patterns in a catchment area-dependent manner.
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| 7. |
- Osbeck, Christofer M. G., et al.
(författare)
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Divergent gene expression responses in two Baltic Sea heterotrophic model bacteria to dinoflagellate dissolved organic matter
- 2022
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 17:11
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Tidskriftsartikel (refereegranskat)abstract
- Phytoplankton release massive amounts of dissolved organic matter (DOM) into the water column during recurring blooms in coastal waters and inland seas. The released DOM encompasses a complex mixture of both known and unknown compounds, and is a rich nutrient source for heterotrophic bacteria. The metabolic activity of bacteria during and after phytoplankton blooms can hence be expected to reflect the characteristics of the released DOM. We therefore investigated if bacterioplankton could be used as "living sensors" of phytoplankton DOM quantity and/or quality, by applying gene expression analyses to identify bacterial metabolisms induced by DOM. We used transcriptional analysis of two Baltic Sea bacterial isolates (Polaribacter sp. BAL334 [Flavobacteriia] and Brevundimonas sp. BAL450 [Alphaproteobacteria]) growing with DOM from axenic cultures of the dinoflagellate Prorocentrum minimum. We observed pronounced differences between the two bacteria both in growth and the expressed metabolic pathways in cultures exposed to dinoflagellate DOM compared with controls. Differences in metabolic responses between the two isolates were caused both by differences in gene repertoire between them (e.g. in the SEED categories for membrane transport, motility and photoheterotrophy) and the regulation of expression (e.g. fatty acid metabolism), emphasizing the importance of separating the responses of different taxa in analyses of community sequence data. Similarities between the bacteria included substantially increased expression of genes for Ton and Tol transport systems in both isolates, which are commonly associated with uptake of complex organic molecules. Polaribacter sp. BAL334 showed stronger metabolic responses to DOM harvested from exponential than stationary phase dinoflagellates (128 compared to 26 differentially expressed genes), whereas Brevundimonas sp. BAL450 responded more to the DOM from stationary than exponential phase dinoflagellates (33 compared to 6 differentially expressed genes). These findings suggest that shifts in bacterial metabolisms during different phases of phytoplankton blooms can be detected in individual bacterial species and can provide insights into their involvement in DOM transformations.
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| 8. |
- Osbeck, Christofer M. G., et al.
(författare)
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Divergent transcriptional responses of Baltic Sea bacteria to forest and agriculture river loadings
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Climate change is projected to induce substantial changes in precipitation patterns across the globe. In Northern Europe, precipitation is expected to increase more than the global average (particularly in northern Scandinavia), causing increased river runoff. The Baltic Sea is one of the largest brackish environments on earth with a catchment area that spans 14 countries, encompassing primarily forested areas and agricultural landscapes. Despite the acknowledged role of marine bacteria in nutrient cycling, there is a lack of knowledge in their metabolic responses to inorganic and organic nutrient loading from riverine runoff. We investigated the bacterial growth and gene expression responses in a mesocosm experiment in which river water from boreal forest- (enriched in humic substances) or agriculture-influenced catchment areas (enriched in nitrogen) were added to Baltic Proper water. The riverine nutrient input triggered extensive phytoplankton blooms and bacterial growth, most notably in the agriculture river treatment. Interestingly, bacterial gene expression analysis (metatranscriptomics) showed similar responses to agriculture and humic river inputs at the start of the experiment during phytoplankton development, but expression patterns diverged upon bloom senescence. This indicated that interactions between river nutrient loading and phytoplankton organic matter are important in regulating bacterial activities and responses at the molecular level. Notably, transcripts associated with phosphate metabolism were significantly enriched in the agriculture river treatment compared to the boreal forest river treatment, whereas transcripts related to nitrogen metabolism were significantly lower. The opposite pattern was observed in the boreal forest river water treatment. This suggests that bacterial transformations of organic matter and nutrient processing in coastal environments are sensitive to alterations in the precipitation-induced riverine runoff in a catchment area-dependent manner, which has implications for interpreting the ecosystem effects of globally changing precipitation patterns.
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| 9. |
- Pinhassi, Jarone, et al.
(författare)
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Functional responses of key marine bacteria to environmental change - toward genetic counselling for coastal waters
- 2022
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Ingår i: Frontiers in Microbiology. - : Frontiers Media S.A.. - 1664-302X. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Coastal ecosystems deteriorate globally due to human-induced stress factors, like nutrient loading and pollution. Bacteria are critical to marine ecosystems, e.g., by regulating nutrient cycles, synthesizing vitamins, or degrading pollutants, thereby providing essential ecosystem services ultimately affecting economic activities. Yet, until now bacteria are overlooked both as mediators and indicators of ecosystem health, mainly due to methodological limitations in assessing bacterial ecosystem functions. However, these limitations are largely overcome by the advances in molecular biology and bioinformatics methods for characterizing the genetics that underlie functional traits of key bacterial populations - "key" in providing important ecosystem services, being abundant, or by possessing high metabolic rates. It is therefore timely to analyze and define the functional responses of bacteria to human-induced effects on coastal ecosystem health. We posit that categorizing the responses of key marine bacterial populations to changes in environmental conditions through modern microbial oceanography methods will allow establishing the nascent field of genetic counselling for our coastal waters. This requires systematic field studies of linkages between functional traits of key bacterial populations and their ecosystem functions in coastal seas, complemented with systematic experimental analyses of the responses to different stressors. Research and training in environmental management along with dissemination of results and dialogue with societal actors are equally important to ensure the role of bacteria is understood as fundamentally important for coastal ecosystems. Using the responses of microorganisms as a tool to develop genetic counselling for coastal ecosystems can ultimately allow for integrating bacteria as indicators of environmental change.
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| 10. |
- Tamas, Ivica, et al.
(författare)
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Endosymbiont gene functions impaired and rescued by polymerase infidelity at poly(A) tracts
- 2008
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 105:39, s. 14934-14939
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Tidskriftsartikel (refereegranskat)abstract
- Among host-dependent bacteria that have evolved by extreme reductive genome evolution, long-term bacterial endosymbionts of insects have the smallest (160-790 kb) and most A + T-rich (>70%) bacterial genomes known to date. These genomes are riddled with poly(A) tracts, and 5-50% of genes contain tracts of 10 As or more. Here, we demonstrate transcriptional slippage at poly(A) tracts within genes of Buchnera aphidicola associated with aphids and Blochmannia pennsylvanicus associated with ants. Several tracts contain single frameshift deletions; these apparent pseudogenes showed patterns of constraint consistent with purifying selection on the encoded proteins. Transcriptional slippage yielded a heterogeneous population of transcripts with variable numbers of As in the tract. Across several frameshifted genes, including B. aphidicola cell wall biosynthesis genes and a B. pennsylvanicus histidine biosynthesis gene, 12-50% of transcripts contained corrected reading frames that could potentially yield full-length proteins. In situ immunostaining confirmed the production of the cell wall biosynthetic enzyme UDP-N-acetylmuramyl pentapeptide synthase encoded by the frameshifted murF gene. Simulation studies indicated an overrepresentation of poly(A) tracts in endosymbiont genomes relative to other A + T-rich bacterial genomes. Polymerase infidelity at poly(A) tracts rescues the functionality of genes with frameshift mutations and, conversely, reduces the efficiency of expression for in-frame genes carrying poly(A) regions. These features of homopolymeric tracts could be exploited to manipulate gene expression in small synthetic genomes.
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