Suchergebnisse

Seagrasses play an important role as ecosystem engineers; they provide shelter to many animals and improve water quality by filtering out nutrients and by controlling pathogens. Moreover, their rhizosphere promotes a myriad of microbial interactions and processes, which are dominated by microorganisms involved in the sulfur cycle. This study provides a detailed insight into the metabolic sulfur pathways in the rhizobiome of the seagrass Zostera marina, a dominant seagrass species across the temperate northern hemisphere. Shotgun metagenomic sequencing revealed the relative dominance of Gamma- and Deltaproteobacteria, and comparative analysis of sulfur genes identified a higher abundance of genes related to sulfur oxidation than sulfate reduction. We retrieved four high-quality draft genomes that are closely related to the gill symbiont of the clam Solemya velum, which suggests the presence of putative free-living forms of symbiotic bacteria. These are potentially highly versatile chemolithoautotrophic bacteria, able to alternate their metabolism between parallel pathways of sulfide oxidation (via sqr and fcc), nitrate reduction (denitrification or DNRA) and carbon fixation (via CBB or TCA cycle), depending on the environmental availability of sulfide. Our results support the hypothesis that seagrass meadows might function as a source of symbionts for invertebrates that inhabit within or around seagrass meadows. While providing ideal conditions for the proliferation of these free-living forms of symbionts, seagrasses would benefit from their genetic versatility, which contributes to sulfide detoxification and ammonium production, the seagrasses' preferred nitrogen source. ; European Union ERC 322551 European Science Foundation ConGenOmics program 6349 Fundacao para a Ciencia e Tecnologia (FCT) SFRH/BPD/63/03/2009 SFRH/BPD/107878/2015 ; info:eu-repo/semantics/publishedVersion

10 pages, 6 figures, 1 table. ; The planktonic archaeal assemblages of several anaerobic, sulfide-rich, aquatic environments were analyzed in space and time by PCR-denaturing gradient gel electrophoresis and sequencing of 16S rRNA gene fragments. The systems were sampled in different years between 1992 and 1998. PCR products were obtained directly from the original DNA without previous nested amplification and yielded successful fingerprints with mostly sharp bands in the gel. Nineteen samples from the anaerobic hypolimnia of 8 lakes and 1 coastal lagoon in NE Spain, Mallorca and Switzerland were compared and a temporal survey was carried out in one of the lakes (Lake Vilar). Between 4 and 14 well-defined bands appeared. All the sequenced bands belonged to Archaea. Although most of the water bodies shared the same climatic conditions and presence of sulfide, the limnological parameters were different among them and different fingerprints were observed in different lakes. Euryarchaeota, i.e., methanogen- and thermoplasma-related sequences, appeared in all the samples but crenarchaeota were recovered only from Lake Vilar. A temporal shift in the predominant members of the archaeal assemblage from crenarchaeota to members of the cluster of thermoplasmales and relatives took place in Lake Vilar between February and June. Sequences related to thermoplasmales and crenarchaeota were distantly related to cultured strains (81% similarity in 16S rDNA) and clustered with branches represented only by environmental clones, whereas sequences related to methanogens grouped with a sequence from an endosymbiont of 1 anaerobic ciliate. A new branch of freshwater euryarchaeota appeared within the cluster of thermoplasmales and relatives. Our study indicates the presence of dynamic archaeal populations in the water column of nonthermophilic, sulfide-rich environments, further extending the diversity and distribution of Archaea in nature. The temporal shift in community composition in Lake Vilar suggests that Archaea grow under in situ conditions. If this is the case, Archaea would be active players in the anaerobic biogeochemical cycles of these environments ; This work was financed by the Max Planck Society in Germany, by DGICyT grant number PB95-0222 from the Spanish Ministerio de Educación y Cultura and by project MIDAS (Microbial Diversity in Aquatic Systems, MAS3-CT97-0154) from the European Union. ; Peer reviewed