Obligate sulfide-dependent degradation of methoxylated aromatic compounds and formation of methanethiol and dimethyl sulfide by a freshwater sedimentisolate, Parasporobacterium paucivorans gen. nov., sp nov.

Methanethiol (MT) and dimethyl sulfide (DMS) have been shown to be the domi nant volatile organic sulfur compounds in freshwater sediments. Previous re search demonstrated that in these habitats NIT and DMS are derived mainly f rom the methylation of sulfide. In order to identify the microorganisms tha t are responsible for this type of NIT and DMS formation, several sulfide-r ich freshwater sediments were amended with two potential methyl group-donat ing compounds, syringate and 3,4,5-trimethoxybenzoate (0.5 mM). The additio n of these methoxylated aromatic compounds resulted in excess accumulation of MT and DMS in all sediment slurries even though methanogenic consumption of NIT and DMS occurred. From one of the sediment slurries tested, a novel anaerobic bacterium was isolated with syringate as the sole carbon source. The strain, designated Parasporobacterium paucivorans, produced NIT and DM S from the methoxy groups of syringate. The hydroxylated aromatic residue ( gallate) was converted to acetate and butyrate. Like Sporobacterium oleariu m, another methoxylated aromatic compound-degrading bacterium, the isolate is a member of the XIVa cluster of the low-GC-content Clostridiales group. However, the new isolate differs from all other known methoxylated aromatic compound-degrading bacteria because it was able to degrade syringate in si gnificant amounts only in the presence of sulfide.