Summary
Until now anaerobic oxidation of VFA at high salt‐pH has been demonstrated only at sulfate‐reducing conditions. Here, we present results of a microbiological investigation of anaerobic conversion of organic acids and alcohols at methanogenic conditions by syntrophic associations enriched from hypersaline soda lakes in Central Asia. Sediment incubation experiments showed active, albeit very slow, methane formation from acetate, propionate, butyrate and C
2
C
4
alcohols at pH 10 and various levels of salinity. Enrichments of syntrophic associations using hydrogenotrophic members of the genus
Methanocalculus
from soda lakes as partners resulted in several highly enriched cultures converting acetate, propionate, butyrate, benzoate and EtOH to methane. Most syntrophs belonged to
Firmicutes
, while the propionate‐oxidizer formed a novel lineage within the family
Syntrophobacteraceae
in the
Deltaproteobacteria
. The acetate‐oxidizing syntroph was identified as ‘
Ca
. Syntrophonatronum acetioxidans’ previously found to oxidize acetate at sulfate‐reducing conditions up to salt‐saturating concentrations. Butyrate and a benzoate‐degrading syntrophs represent novel genus‐level lineages in
Syntrophomonadales
which are proposed as Candidatus taxons ‘Syntrophobaca’, ‘Syntrophocurvum’ and ‘Syntropholuna’. Overall, despite very slow growth, the results indicated the presence of a functionally competent syntrophic community in hypersaline soda lakes, capable of efficient oxidation of fermentation products to methane at extremely haloalkaline conditions.