| 1. |
- Rengefors, Karin, et al.
(author)
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Evidence of concurrentlocal adaptation and high phenotypic plasticityin a polar microeukaryote.
- 2015
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In: Environmental Microbiology. - : Wiley. - 1462-2920 .- 1462-2912. ; 17:5, s. 1510-1519
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Journal article (peer-reviewed)abstract
- Here we investigated whether there is evidence of local adaptation in strains of an ancestrallymarine dinoflagellate to the lacustrine environment they now inhabit(optimal genotypes) and/orif they have evolved phenotypic plasticity (a range of phenotypes). Eleven strains of Polarella glacialis were isolated and cultured from three different environments: the polar seas, ahyposaline,and a hypersaline Antarctic lake. Local adaptation was tested by comparing growth rates of lacustrine and marine strains at their own and reciprocal site conditions. To determine phenotypic plasticity, we measured thereaction norm for salinity.We found evidence of both, limitedlocal adaptation andhigherphenotypic plasticity in lacustrine strains when compared tomarine ancestors. At extreme high salinities,local lake strains outperformed otherstrains, and at extreme low salinities, strains from the hyposaline lake outperformed all other strains. The data suggest that lake populations may have evolved higher phenotypic plasticity in the lake habitats compared to the sea, presumably due to the high temporal variability in salinity in the lacustrine systems. Moreover, the interval of salinity tolerance differed between strains from the hyposalineand hypersaline lakes, indicatinglocal adaptation promoted by different salinity.
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| 2. |
- Klawonn, Isabell, et al.
(author)
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Cell-specific nitrogen- and carbon-fixation of cyanobacteria in a temperate marine system (Baltic Sea)
- 2016
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In: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920 .- 1758-2229. ; 18:12, s. 4596-4609
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Journal article (peer-reviewed)abstract
- We analysed N2- and carbon (C) fixation in individual cells of Baltic Sea cyanobacteria by combining stable isotope incubations with secondary ion mass spectrometry (SIMS). Specific growth rates based on N2- and C-fixation were higher for cells of Dolichospermum spp. than for Aphanizomenon sp. and Nodularia spumigena. The cyanobacterial biomass, however, was dominated by Aphanizomenon sp., which contributed most to total N2-fixation in surface waters of the Northern Baltic Proper. N2-fixation by Pseudanabaena sp. and colonial picocyanobacteria was not detectable. N2-fixation by Aphanizomenon sp., Dolichospermum spp. and N. spumigena populations summed up to total N2-fixation, thus these genera appeared as sole diazotrophs within the Baltic Sea's euphotic zone, while their mean contribution to total C-fixation was 21%. Intriguingly, cell-specific N2-fixation was 8-fold higher at a coastal station compared to an offshore station, revealing coastal zones as habitats with substantial N2-fixation. At the coastal station, the cell-specific C- to N2-fixation ratio was below the cellular C:N ratio, i.e., N2 was assimilated in excess to C-fixation, whereas the C- to N2-fixation ratio exceeded the C:N ratio in offshore sampled diazotrophs. Our findings highlight SIMS as a powerful tool not only for qualitative but also for quantitative N2-fixation assays in aquatic environments.
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| 3. |
- Abreu, Fernanda, et al.
(author)
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Culture-independent characterization of a novel magnetotactic member affiliated to the Beta class of the Proteobacteria phylum from an acidic lagoon
- 2018
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In: Environmental Microbiology. - : Wiley/Blackwell. - 1462-2912 .- 1462-2920. ; 20:7, s. 2615-2624
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Journal article (peer-reviewed)abstract
- Summary Magnetotactic bacteria (MTB) comprise a group of motile microorganisms common in most mesothermal aquatic habitats with pH values around neutrality. However, during the last two decades, a number of MTB from extreme environments have been characterized including: cultured alkaliphilic strains belonging to the Deltaproteobacteria class of the Proteobacteria phylum; uncultured moderately thermophilic strains belonging to the Nitrospirae phylum; cultured and uncultured moderately halophilic or strongly halotolerant bacteria affiliated with the Deltaproteobacteria and Gammaproteobacteria classes and an uncultured psychrophilic species belonging to the Alphaproteobacteria class. Here, we used culture-independent techniques to characterize MTB from an acidic freshwater lagoon in Brazil (pH ? 4.4). MTB morphotypes found in this acidic lagoon included cocci, rods, spirilla and vibrioid cells. Magnetite (Fe3O4) was the only mineral identified in magnetosomes of these MTB while magnetite magnetosome crystal morphologies within the different MTB cells included cuboctahedral (present in spirilla), elongated prismatic (present in cocci and vibrios) and bullet-shaped (present in rod-shaped cells). Intracellular pH measurements using fluorescent dyes showed that the cytoplasmic pH was close to neutral in most MTB cells and acidic in some intracellular granules. Based on 16S rRNA gene phylogenetic analyses, some of the retrieved gene sequences belonged to the genus Herbaspirillum within the Betaproteobacteria class of the Proteobacteria phylum. Fluorescent in situ hybridization using a Herbaspirillum-specific probe hybridized with vibrioid MTB in magnetically-enriched samples. Transmission electron microscopy of the Herbaspirillum-like MTB revealed the presence of many intracellular granules and a single chain of elongated prismatic magnetite magnetosomes. Diverse populations of MTB have not seemed to have been described in detail in an acid environment. In addition, this is the first report of an MTB phylogenetically affiliated with Betaproteobacteria class.
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| 4. |
- Ji, Boyang, 1983, et al.
(author)
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The chimeric nature of the genomes of marine magnetotactic coccoid-ovoid bacteria defines a novel group of Proteobacteria
- 2017
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In: Environmental Microbiology. - : Wiley. - 1462-2920 .- 1462-2912. ; 19:3, s. 1103-1119
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Journal article (peer-reviewed)abstract
- Magnetotactic bacteria (MTB) are a group of phylogenetically and physiologically diverse Gram-negative bacteria that synthesize intracellular magnetic crystals named magnetosomes. MTB are affiliated with three classes of Proteobacteria phylum, Nitrospirae phylum, Omnitrophica phylum and probably with the candidate phylum Latescibacteria. The evolutionary origin and physiological diversity of MTB compared with other bacterial taxonomic groups remain to be illustrated. Here, we analysed the genome of the marine magneto-ovoid strain MO-1 and found that it is closely related to Magnetococcus marinus MC-1. Detailed analyses of the ribosomal proteins and whole proteomes of 390 genomes reveal that, among the Proteobacteria analysed, only MO-1 and MC-1 have coding sequences (CDSs) with a similarly high proportion of origins from Alphaproteobacteria, Betaproteobacteria, Deltaproteobacteria and Gammaproteobacteria. Interestingly, a comparative metabolic network analysis with anoxic network enzymes from sequenced MTB and non-MTB successfully allows the eventual prediction of an organism with a metabolic profile compatible for magnetosome production. Altogether, our genomic analysis reveals multiple origins of MO-1 and M. marinus MC-1 genomes and suggests a metabolism-restriction model for explaining whether a bacterium could become an MTB upon acquisition of magnetosome encoding genes.
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| 5. |
- Liotenberg, Sylviane, et al.
(author)
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Oxygen-dependent copper toxicity: targets in the chlorophyll biosynthesis pathway identified in the copper efflux ATPase CopA deficient mutant
- 2015
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In: Environmental Microbiology. - : Wiley. - 1462-2920 .- 1462-2912. ; 17, s. 1963-1976
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Journal article (peer-reviewed)abstract
- Characterization of a copA(-) mutant in the purple photosynthetic bacterium Rubrivivax gelatinosus under low oxygen or anaerobic conditions, as well as in the human pathogen Neisseria gonorrhoeae identified HemN as a copper toxicity target enzyme in the porphyrin synthesis pathway. Heme synthesis is, however, unaffected by copper under high oxygen tension because of the aerobic coproporphyrinogen III oxidase HemF. Nevertheless, in the copA(-) mutant under aerobiosis, we show that the chlorophyll biosynthesis pathway is affected by excess copper resulting in a substantial decrease of the photosystem. Analyses of pigments and enzyme activity showed that under low copper concentrations, the mutant accumulated protochlorophyllide, suggesting that the protochlorophyllide reductase activity is affected by excess copper. Increase of copper concentration led to a complete lack of chlorophyll synthesis as a result of the loss of Mg-chelatase activity. Both enzymes are widely distributed from bacteria to plants; both are [4Fe-4S] proteins and oxygen sensitive; our data demonstrate their in vivo susceptibility to copper in the presence of oxygen. Additionally, our study provides the understanding of molecular mechanisms that may contribute to chlorosis in plants when exposed to metals. The role of copper efflux systems and the impact of copper on heme and chlorophyll biosynthesis in phototrophs are addressed
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| 6. |
- Logares, Ramiro, et al.
(author)
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Contrasting prevalence of selection and drift in the community structuring of bacteria and microbial eukaryotes
- 2018
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In: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 20:6, s. 2231-2240
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Journal article (peer-reviewed)abstract
- Whether or not communities of microbial eukaryotes are structured in the same way as bacteria is a general and poorly explored question in ecology. Here, we investigated this question in a set of planktonic lake microbiotas in Eastern Antarctica that represent a natural community ecology experiment. Most of the analysed lakes emerged from the sea during the last 6000 years, giving rise to waterbodies that originally contained marine microbiotas and that subsequently evolved into habitats ranging from freshwater to hypersaline. We show that habitat diversification has promoted selection driven by the salinity gradient in bacterial communities (explaining approximate to 72% of taxa turnover), while microeukaryotic counterparts were predominantly structured by ecological drift (approximate to 72% of the turnover). Nevertheless, we also detected a number of microeukaryotes with specific responses to salinity, indicating that albeit minor, selection has had a role in the structuring of specific members of their communities. In sum, we conclude that microeukaryotes and bacteria inhabiting the same communities can be structured predominantly by different processes. This should be considered in future studies aiming to understand the mechanisms that shape microbial assemblages.
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| 7. |
- Münzner, Karla, et al.
(author)
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In situ plankton community respiration measurements show low respiratory quotients in a eutrophic lake
- 2019
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In: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 21:4, s. 1425-1435
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Journal article (peer-reviewed)abstract
- Planktonic community respiration is an important carbon cycling process, typically quantified by converting measured values of dissolved O2 consumption rates into CO2 production rates assuming a respiratory quotient of 1 (RQ = CO2 per O2 by moles). However, the true variability in planktonic RQs between different aquatic ecosystems is poorly understood. We conducted in situ RQ measurements in a eutrophic lake dominated by algal‐derived substances and found that RQs were significantly below 1. In fact, many RQ values were extremely low (0.2–0.6), below theoretical RQs for oxidation of algal organic matter substrates (0.7–0.8), suggesting that other factors than substrate control need to be considered to understand the RQ. This view was further supported by lack of correlations between RQ and microbial variables known to be strongly substrate dependent, including bacterial growth efficiency and the functional capacity of the bacterioplankton community to degrade different compounds. Based on the measured dynamics in methane and nutrient pools, we discuss that methane oxidation and nitrification likely occurred in the lake, contributing to the unusually low RQs. Our findings demonstrate that planktonic RQs in productive lakes can systematically be below 1, suggesting that CO2 emissions from these lakes may currently be overestimated.
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| 8. |
- Nedialkova, Lubov Petkova, et al.
(author)
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Temperate phages promote colicin-dependent fitness of Salmonella enterica serovar Typhimurium.
- 2015
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In: Environmental Microbiology. - : Wiley. - 1462-2920 .- 1462-2912. ; 18, s. 1591-1603
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Journal article (peer-reviewed)abstract
- Bacteria employ bacteriocins for interference competition in microbial ecosystems. Colicin Ib (ColIb), a pore-forming bacteriocin, confers a significant fitness benefit to Salmonella enterica serovar Typhimurium (S. Tm) in competition against commensal E. coli in the gut. ColIb is released from S. Tm into the environment, where it kills susceptible competitors. However, colicin-specific release proteins, as they are known for other colicins, have not been identified in case of ColIb. Thus, its release mechanism has remained unclear. In the current study, we have established a new link between ColIb release and lysis activity of temperate, lambdoid phages. By the use of phage-cured S. Tm mutant strains, we show that the presence of temperate phages and their lysis genes is necessary and sufficient for release of active ColIb into the culture supernatant. Furthermore, phage-mediated lysis significantly enhanced S. Tm fitness in competition against a ColIb-susceptible competitor. Finally, transduction with the lambdoid phage 933W rescued the defect of E. coli strain MG1655 with respect to ColIb release. In conclusion, ColIb is released from bacteria in the course of phage lysis. Our data reveal a new mechanism for colicin release and point out a novel function of temperate phages in enhancing colicin-dependent bacterial fitness.
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| 9. |
- Sassenhagen, Ingrid, et al.
(author)
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Freshwater protists do not go with the flow: Population structure in Gonyostomum semen independent of connectivity among lakes
- 2015
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In: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 17:12, s. 5063-5072
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Journal article (peer-reviewed)abstract
- Many recent studies have found genetically differentiated populations in microorganisms despite potentially high dispersal. We designed a study to specifically examine the importance of physical dispersal barriers, i.e. geographic distance and lack of hydrological connectivity, in restricting gene flow and enhancing divergence in limnic microorganisms. We focused on the nuisance microalga Gonyostomum semen, which has recently expanded in Northern Europe and differentiated into genetically distinct populations. G.semen was sampled from six lakes distributed in two adjacent watersheds, which thereby comprised, both connected and non-connected lakes. The individual isolates were genotyped by amplified fragment length polymorphism. Several lake populations were differentiated from each other, but connectivity within watersheds could not explain the observed population genetic pattern. However, isolation by distance was moderate and might limit the gene flow among distant populations. In addition, we found low, but significant linkage disequilibrium, which indicates regular sexual recombination in this species, despite its high degree of asexual reproduction. Therefore, we conclude that the genetic properties of microalgae with occasional sexual reproduction essentially mirror regularly recombining species. Furthermore, the data indicated bottlenecks supporting the hypothesized recent range expansion of this species.
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| 10. |
- Sefbom, Josefin, et al.
(author)
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A planktonic diatom displays genetic structure over small spatial scales
- 2018
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In: Environmental Microbiology. - : Wiley. - 1462-2912 .- 1462-2920. ; 20:8, s. 2783-2795
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Journal article (peer-reviewed)abstract
- Marine planktonic microalgae have potentially global dispersal, yet reduced gene flow has been confirmed repeatedly for several species. Over larger distances (>200 km) geographic isolation and restricted oceanographic connectivity have been recognized as instrumental in driving population divergence. Here we investigated whether similar patterns, that is, structured populations governed by geographic isolation and/or oceanographic connectivity, can be observed at smaller (6-152 km) geographic scales. To test this we established 425 clonal cultures of the planktonic diatom Skeletonema marinoi collected from 11 locations in the Archipelago Sea (northern Baltic Sea). The region is characterized by a complex topography, entailing several mixing regions of which four were included in the sampling area. Using eight microsatellite markers and conventional F-statistics, significant genetic differentiation was observed between several sites. Moreover, Bayesian cluster analysis revealed the co-occurrence of two genetic groups spread throughout the area. However, geographic isolation and oceanographic connectivity could not explain the genetic patterns observed. Our data reveal hierarchical genetic structuring whereby despite high dispersal potential, significantly diverged populations have developed over small spatial scales. Our results suggest that biological characteristics and historical events may be more important in generating barriers to gene flow than physical barriers at small spatial scales.
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