Abstract
Hydrothermal activity can generate numerous and diverse hydrocarbon compounds. However, little is known about the influence of such hydrocarbons on deep-sea hydrothermal microbial ecology. We hypothesize that certain bacteria live on these hydrocarbons. Therefore, in this study, the distribution of hydrocarbons and their associated hydrocarbon-degrading bacteria were investigated at deep-sea hydrothermal vents at the Southern Mid-Atlantic Ridge, the Southwest Indian Ridge, and the East Pacific Rise. A variety of hydrocarbon-degrading consortia were obtained from hydrothermal samples collected at the aforementioned sites after low-temperature enrichment under high hydrostatic pressures, and the bacteria responsible for the degradation of hydrocarbons were investigated by DNA-based stable-isotope probing with uniformly 13C-labeled hydrocarbons. Unusually, we identified several previously recognized sulfur-oxidizing chemoautotrophs as hydrocarbon-degrading bacteria, e.g., the SAR324 group, the SUP05 clade, and Sulfurimonas, and for the first time confirmed their ability to degrade hydrocarbons. In addition, Erythrobacter, Pusillimonas, and SAR202 clade were shown to degrade polycyclic aromatic hydrocarbons for the first time. These results together with relatively high abundance in situ of most of the above-described bacteria highlight the potential influence of hydrocarbons in configuring the vent microbial community, and have made the importance of mixotrophs in hydrothermal vent ecosystems evident.
Highlights
Hydrothermal activity can generate a variety of reduced compounds, including low molecular weight hydrocarbons, which can be produced abiotically through water–rock interactions under high temperature and pressure [1,2,3,4]
We have explored the bacterial diversity involved in polycyclic aromatic hydrocarbons (PAHs) degradation in deep-sea sediments of the Mid-Atlantic Ridge (MAR) [18], the west Pacific [19, 20], and the Arctic [21], as well as in the deepwater columns of the southwest Indian Ridge [22]
The concentration and composition of hydrocarbons were measured in the samples from hydrothermal fields at the southern Mid-Atlantic Ridge (SMAR), southwest Indian Ridge (SWIR), and East Pacific Rise (EPR), and in vent plumes, sulfide chimney samples, and sediments (Table S2)
Summary
Hydrothermal activity can generate a variety of reduced compounds, including low molecular weight hydrocarbons, which can be produced abiotically through water–rock interactions under high temperature and pressure [1,2,3,4]. A high diversity of alkane monooxygenases that were phylogenetically affiliated with enzymes involved in C1–C4 alkane oxidation was observed in the Guaymas Basin hydrothermal plume [14, 15]. Metagenomic and metatranscriptomic approaches revealed the presence of diverse methylcoenzyme M reductase-based alkane-oxidizing archaea, including the multi-carbon alkane oxidizer Ca. Syntrophoarchaeum spp., anaerobic methane-oxidizing archaea (ANME-1 and ANME-2c), and sulfate-reducing bacteria (HotSeep-1 and Seep-SRB2) coexisting with sulfate-reducing bacteria and showed the potential for alkane oxidization in Guaymas Basin hydrothermal sediments [17]. Syntrophoarchaeum spp., anaerobic methane-oxidizing archaea (ANME-1 and ANME-2c), and sulfate-reducing bacteria (HotSeep-1 and Seep-SRB2) coexisting with sulfate-reducing bacteria and showed the potential for alkane oxidization in Guaymas Basin hydrothermal sediments [17] These advances are mainly based on metadata, while few hydrocarbon-oxidizing microbes have been isolated from deep ecosystems
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