Heterotrophic Proteobacteria in the vicinity of diffuse hydrothermal venting

Abstract

Deep-sea hydrothermal vents are highly dynamic habitats characterized by steep temperature and chemical gradients. The oxidation of reduced compounds dissolved in the venting fluids fuels primary production providing the basis for extensive life. Until recently studies of microbial vent communities have focused primarily on chemolithoautotrophic organisms. In our study, we targeted the change of microbial community compositions along mixing gradients, focusing on distribution and capabilities of heterotrophic microorganisms. Samples were retrieved from different venting areas within the Menez Gwen hydrothermal field, taken along mixing gradients, including diffuse fluid discharge points, their immediate surroundings and the buoyant parts of hydrothermal plumes. High throughput 16S rRNA gene amplicon sequencing, fluorescence in situ hybridization, and targeted metagenome analysis were combined with geochemical analyses. Close to diffuse venting orifices dominated by chemolithoautotrophic Epsilonproteobacteria, in areas where environmental conditions still supported chemolithoautotrophic processes, we detected microbial communities enriched for versatile heterotrophic Alpha- and Gammaproteobacteria. The potential for alkane degradation could be shown for several genera and yet uncultured clades. We propose that hotspots of chemolithoautotrophic life support a 'belt' of heterotrophic bacteria significantly different from the dominating oligotrophic microbiota of the deep sea.

Spatially distinct, temporally stable microbial populations mediate biogeochemical cycling at and below the seafloor in hydrothermal vent fluids

“…() showed that patterns in abundance of Epsilonbacteraeota at Axial Seamount were correlated to vent methane concentrations as well as vent location, while at the Menez Gwen vent field, Meier et al . () found a transition from chemolithoautotrophic communities close to sources of venting to heterotrophic communities with increasing distance from the venting source.…”

“…() showed that there were fine‐scale phylogenetic differences in microbial community structure between the two vent fields, with fluid communities at each vent field more closely related to one another than communities found in fluids from the other vent field. In addition, smaller scale spatial studies of multiple diffuse vents within one vent field (Huber et al ., ; Opatkiewicz et al ., ; Perner et al ., ; Akerman et al ., ; Meier et al ., ; Olins et al ., ) show that the microbial community composition is shaped by both the geochemistry as well as the distance between individual diffuse vents. For example, Akerman et al .…”

Productivity, metabolism and physiology of free-living chemoautotrophic Epsilonproteobacteria

“…In this case, the sampled fluids in our study would not contain large populations of methanotrophs. This appears to be the case at the Menez Gwen hydrothermal vent field, where metagenomes indicate the absence of known methane-oxidizing genes (Meier et al, 2016), despite the end-member fluids being rich in methane (Charlou et al, 2000).…”

“…At such a site, microbes will be exposed to steep gradients of temperature and redox state on a small spatial scale (mm to cm). This can affect microbial population structures, with more thermophilic representatives found in such environments (Meier et al, 2016 1.4…”

“…Therefore, while subseafloor chemosynthesis can vastly increase carbon for consumers locally, it will be ultimately confined to a relatively small area near active venting. A recent study showed heterotrophic bacteria with the potential to degrade diverse organic substrates are clustered around low-temperature vents (Meier et al, 2016), which 1 See methods for details may indicate that chemosynthetic production is closely coupled to remineralization.…”