Description of new species and most efficient methanogenic consortia in methane generation
Microbial communities from sediments of S'Avall demonstrated an understudied potential in methanogenesis, and halophilic methanogenic consortia from enriched microcosms were described in this study by means of metagenomics. With a broad range in cultivability requirements at eight different salinities, distinct substrate concentrations and ampicillin, the most efficient microcosms were selected in accordance to gas methane measurement through gas chromatography.  These enrichments were sub-cultured and supplemented with organic compounds (acetate, formate and trimethylamine: ATF), which enhanced the methane production. The results showed the highest methane yield in microcosms at 5% of salinity with ampicillin and 10% w/w P. oceanica, and even more the supplemented with ATF, obtaining higher methane rates in comparison to reported until now. Among the prokaryotic diversity regarding the ATF supplement availability, Methanosarcina was more abundant in the no supplemented enrichment, whereas Methanoculleus with ATF. These genera within Methanomicrobia showed a taxonomic turnover in accordance to the supplement disposal. Besides, aceticlastic Methanoculleus genus exhibited high replication activity in comparison to the metabolically versatile Methanosarcina, which can produce methane using any of the methanogenesis pathways. Additionally, new members of Bathyarchaeia and Lokiarchaeia were also able to produce methane, specially Bathyarchaeia in the no-ATF supplemented enrichment and the putative hydrogenotrophic Lokiarchaeia class in the supplemented one. In fact, methanogenesis was performed mainly via aceticlastic route, with Methanomicrobia and Bathyarchaeia as the most representative, and the supplement based on the addition of acetate, trimethylamine and formate could be mainly metabolized by members affiliated with Methanomicrobia and Lokiarchaeia.