Clostridium proteoclasticum: a ruminal bacterium that forms stearic acid from linoleic acid

The aim of this study was to identify ruminal bacteria that form stearic acid (18 : 0) from linoleic acid (cis-9,cis-12-18 : 2). One 18 : 0-producing isolate, P-18, isolated from the sheep rumen was similar in morphology and metabolic properties to ‘Fusocillus’ spp. isolated many years ago. Phylogenetic analysis based on nearly fulllength 16S rRNA gene sequence (41300 bp) analysis indicated that the stearate producer was most closely related to Clostridium proteoclasticum B316T. Clostridium proteoclasticum B316T was also found to form 18 : 0, as were other bacteria isolated elsewhere, which occurred in the same family subclass of the low G1C% Gram-positive bacteria, related to Butyrivibrio fibrisolvens. These bacteria are not clostridia, and the ability to form 18 : 0 was present in all strains in contrast to proteolytic activity, which was variable. Production of 18 : 0 occurred in growing, but not in stationary-phase, bacteria, which made detection of biohydrogenating activity difficult, because of the inhibitory effects of linoleic acid on growth.