Dataset Information

Obtaining Genome Sequences of Mutualistic Bacteria in Single Microcystis Colonies.

ABSTRACT: Cells of Microcystis are associated with heterotrophic bacteria and organized in colonies in natural environment, which are basic elements in the mass occurrence of cyanobacterial species. Analyzing these colonies by using metagenomics is helpful to understand species composition and relationship. Meanwhile, the difference in population abundance among Microcystis colonies could be used to recover genome bins from metagenome assemblies. Herein, we designed a pipeline to obtain high-quality genomes of mutualistic bacteria from single natural Microcystis colonies. Single colonies were lysed, and then amplified by using multiple displacement amplification to overcome the DNA quantity limit. A two-step assembly was performed after sequencing and scaffolds were grouped into putative bins based on their differential-coverage among species. We analyzed six natural colonies of three prevailing Microcystis species from Lake Taihu. Clustering results proved that colonies of the same species were similar in the microbial community composition. Eight putative population genome bins with wide bacterial diversity and different GC content were identified based on coverage difference among colonies. At the phylum level, proteobacteria was the most abundant besides cyanobacteria. Six of the population bins were further refined into nearly complete genomes (completeness > 90%).

SUBMITTER: Tu J

PROVIDER: S-EPMC6829522 | biostudies-literature | 2019 Oct

REPOSITORIES: biostudies-literature

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Obtaining Genome Sequences of Mutualistic Bacteria in Single Microcystis Colonies.

Tu Jing J Chen Liang L Gao Shen S Zhang Junyi J Bi Changwei C Tao Yuhan Y Lu Na N Lu Zuhong Z

International journal of molecular sciences 20191011 20

Cells of Microcystis are associated with heterotrophic bacteria and organized in colonies in natural environment, which are basic elements in the mass occurrence of cyanobacterial species. Analyzing these colonies by using metagenomics is helpful to understand species composition and relationship. Meanwhile, the difference in population abundance among Microcystis colonies could be used to recover genome bins from metagenome assemblies. Herein, we designed a pipeline to obtain high ...[more]

PMID: 31614621

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Project description:BackgroundCyanobacteria from the genus Microcystis can form large mucilaginous colonies with attached heterotrophic bacteria-their microbiome. However, the nature of the relationship between Microcystis and its microbiome remains unclear. Is it a long-term, evolutionarily stable association? Which partners benefit? Here we report the genomic diversity of 109 individual Microcystis colonies-including cyanobacteria and associated bacterial genomes-isolated in situ and without culture from Lake Champlain, Canada and Pampulha Reservoir, Brazil.ResultsWe identified 14 distinct Microcystis genotypes from Canada, of which only two have been previously reported, and four genotypes specific to Brazil. Microcystis genetic diversity was much greater between than within colonies, consistent with colony growth by clonal expansion rather than aggregation of Microcystis cells. We also identified 72 bacterial species in the microbiome. Each Microcystis genotype had a distinct microbiome composition, and more closely related genotypes had more similar microbiomes. This pattern of phylosymbiosis could be explained by co-phylogeny in only two out of the nine most prevalent associated bacterial genera, Roseomonas and Rhodobacter. These phylogenetically associated genera could enrich the metabolic repertoire of Microcystis, for example by encoding the biosynthesis of complementary carotenoid molecules. In contrast, other colony-associated bacteria showed weaker signals of co-phylogeny, but stronger evidence of horizontal gene transfer with Microcystis. These observations suggest that acquired genes are more likely to be retained in both partners (Microcystis and members of its microbiome) when they are loosely associated, whereas one gene copy is sufficient when the association is physically tight and evolutionarily long-lasting.ConclusionsWe have introduced a method for culture-free isolation of single colonies from nature followed by metagenomic sequencing, which could be applied to other types of microbes. Together, our results expand the known genetic diversity of both Microcystis and its microbiome in natural settings, and support their long-term, specific, and potentially beneficial associations. Video Abstract.

Project description:The dynamics of growth of bacterial populations has been extensively studied for planktonic cells in well-agitated liquid culture, in which all cells have equal access to nutrients. In the real world, bacteria are more likely to live in physically structured habitats as colonies, within which individual cells vary in their access to nutrients. The dynamics of bacterial growth in such conditions is poorly understood, and, unlike that for liquid culture, there is not a standard broadly used mathematical model for bacterial populations growing in colonies in three dimensions (3-d). By extending the classic Monod model of resource-limited population growth to allow for spatial heterogeneity in the bacterial access to nutrients, we develop a 3-d model of colonies, in which bacteria consume diffusing nutrients in their vicinity. By following the changes in density of E. coli in liquid and embedded in glucose-limited soft agar, we evaluate the fit of this model to experimental data. The model accounts for the experimentally observed presence of a sub-exponential, diffusion-limited growth regime in colonies, which is absent in liquid cultures. The model predicts and our experiments confirm that, as a consequence of inter-colony competition for the diffusing nutrients and of cell death, there is a non-monotonic relationship between total number of colonies within the habitat and the total number of individual cells in all of these colonies. This combined theoretical-experimental study reveals that, within 3-d colonies, E. coli cells are loosely packed, and colonies produce about 2.5 times as many cells as the liquid culture from the same amount of nutrients. We verify that this is because cells in liquid culture are larger than in colonies. Our model provides a baseline description of bacterial growth in 3-d, deviations from which can be used to identify phenotypic heterogeneities and inter-cellular interactions that further contribute to the structure of bacterial communities.

Project description:Scleractinian corals form symbiotic relationships with a variety of microorganisms, including endosymbiotic dinoflagellates of the family Symbiodiniaceae, and with bacteria, which are collectively termed coral holobionts. Interactions between hosts and their symbionts are critical to the physiological status of corals. Coral-microorganism interactions have been studied extensively, but dinoflagellate-bacterial interactions remain largely unexplored. Here, we developed a microbiome manipulation method employing KAS-antibiotic treatment (kanamycin, ampicillin, and streptomycin) to favor pigmented bacteria residing on cultured Cladocopium and Durusdinium, major endosymbionts of corals, and isolated several carotenoid-producing bacteria from cell surfaces of the microalgae. Following KAS-antibiotic treatment of Cladocopium sp. strain NIES-4077, pigmented bacteria increased 8-fold based on colony-forming assays from the parental strain, and 100% of bacterial sequences retrieved through 16S rRNA amplicon sequencing were affiliated with the genus Maribacter. Microbiome manipulation enabled host microalgae to maintain higher maximum quantum yield of photosystem II (variable fluorescence divided by maximum fluorescence [Fv/Fm]) under light-stress conditions, compared to the parental strain. Furthermore, by combining culture-dependent and -independent techniques, we demonstrated that species of the family Symbiodiniaceae and pigmented bacteria form strong interactions. Dinoflagellates protected bacteria from antibiotics, while pigmented bacteria protected microalgal cells from light stress via carotenoid production. Here, we describe for the first time a symbiotic relationship in which dinoflagellates and bacteria mutually reduce environmental stress. Investigations of microalgal-bacterial interactions further document bacterial contributions to coral holobionts and may facilitate development of novel techniques for microbiome-mediated coral reef conservation. IMPORTANCE Coral reefs cover less than 0.1% of the ocean floor, but about 25% of all marine species depend on coral reefs at some point in their life cycles. However, rising ocean temperatures associated with global climate change are a serious threat to coral reefs, causing dysfunction of the photosynthetic apparatus of endosymbiotic microalgae of corals, and overproducing reactive oxygen species harmful to corals. We manipulated the microbiome using an antibiotic treatment to favor pigmented bacteria, enabling their symbiotic microalgal partners to maintain higher photosynthetic function under insolation stress. Furthermore, we investigated mechanisms underlying microalgal-bacterial interactions, describing for the first time a symbiotic relationship in which the two symbionts mutually reduce environmental stress. Our findings extend current insights about microalgal-bacterial interactions, enabling better understanding of bacterial contributions to coral holobionts under stressful conditions and offering hope of reducing the adverse impacts of global warming on coral reefs.

Dataset Information

Obtaining Genome Sequences of Mutualistic Bacteria in Single Microcystis Colonies.

Publications

Obtaining Genome Sequences of Mutualistic Bacteria in Single <i>Microcystis</i> Colonies.

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