RESUMO
Water column and sediment samples were collected in the southern Gulf of Mexico (GoMex) during 3 oceanographic cruises: XIXIMI-04 (September 2015), XIXIMI-05 (June 2016), and XIXIMI-06 (August 2017). DNA that was extracted from the samples was analyzed by qPCR to detect and quantify bacterial groups that have been reported to metabolize alkanes (Alcanivorax) and aromatic hydrocarbons (Cycloclasticus) and are involved in methane production (Methanomicrobiales). The results were then analyzed with regard to the water masses that are currently detected in the GoMex. Generally, we observed a decrease in the proportion of Alcanivorax and a rise in those of Cycloclasticus and Methanomicrobiales in samples from the surface to deep waters and in sediment samples. Scatterplots of the results showed that the relative abundance of the 3 groups was higher primarily from the surface to 1000 m, but the levels of Cycloclasticus and Methanomicrobiales were high in certain water samples below 1000 m and in sediments. In conclusion, oil-degrading bacteria are distributed widely from the surface to deep waters and sediments throughout the southern GoMex, representing a potential inoculum of bacteria for various hydrocarbon fractions that are ready for proliferation and degradation in the event of an oil spill from the seafloor or along the water column.
Assuntos
Biodegradação Ambiental , Sedimentos Geológicos/microbiologia , Microbiologia da Água , Alcanivoraceae , Alcanos/análise , Bactérias/metabolismo , Monitoramento Ambiental , Golfo do México , Hidrocarbonetos/análise , Methanomicrobiales , Petróleo/metabolismo , Poluição por Petróleo/análise , Poluentes Químicos da Água/análiseRESUMO
Methanogenesis was characterized in hypersaline microbial mats from Guerrero Negro, Baja California Sur, Mexico both in situ and after long-term manipulation in a greenhouse environment. Substrate addition experiments indicate methanogenesis to occur primarily through the catabolic demethylation of non-competitive substrates, under field conditions. However, evidence for the coexistence of other metabolic guilds of methanogens was obtained during a previous manipulation of sulfate concentrations. To fully characterize methanogenesis in these mats, in the absence of competition for reducing equivalents with sulfate-reducing microorganisms, we maintained microbial mats for longer than 1 year under conditions of lowered sulfate and salinity levels. The goal of this study was to assess whether observed differences in methane production during sulfate and salinity manipulation were accompanied by shifts in the composition of methanogen communities. Culture-independent techniques targeting methyl coenzyme M reductase genes (mcrA) were used to assess the dynamics of methanogen assemblages. Clone libraries from mats sampled in situ or maintained at field-like conditions in the greenhouse were exclusively composed of sequences related to methylotrophic members of the Methanosarcinales. Increases in pore water methane concentrations under conditions of low sulfate correlated with an observed increase in the abundance of putatively hydrogenotrophic mcrA, related to Methanomicrobiales. Geochemical and molecular data provide evidence of a significant shift in the metabolic pathway of methanogenesis from a methylotroph-dominated system in high-sulfate environments to a mixed community of methylotrophic and hydrogenotrophic methanogens under low sulfate conditions.