ISOLATION AND CHARACTERIZATION OF A NEW BACTERIUM CARBOXYLATING PHENOL TO BENZOIC-ACID UNDER ANAEROBIC CONDITIONS

A consortium of spore-forming bacteria transforming phenol to benzoic acid under anaerobic conditions was treated with antibiotics to elimin ate the four Clostridium strains which were shown to be unable to acco mplish this reaction in pure culture and coculture. Clostridium ghonii was inhibited by chloramphenicol (10 mu g/ml), whereas Clostridium ha stiforme (strain 3) and Clostridium glycolicum were inhibited by clind amycin (20 mu g/ml), without the transformation of phenol being affect ed. Electron microscopic observations of resulting liquid subcultures revealed the presence of two different bacilli: a dominant C. hastifor me strain (strain 2) (width, I mu m) and an unidentified strain 6 (wid th, 0.6 mu m) which was not detected on solid medium. Bacitracin (0.5 U/ml) changed the ratio of the strains in favor of strain 6. C. hastif orme 2 was eliminated from this culture by dilution. The isolated stra in 6 transformed phenol to benzoic acid and 4-hydroxybenzoic acid to p henol and benzoic acid in the presence of proteose peptone. Both of th ese activities are inducible. This strain is a gram-variable, flagella ted rod with a doubling time of 10 to 11 h in the presence of phenol. It has a cellular fatty acid composition like that of C. hastiforme. H owever, strain 6 does not hydrolyze gelatin or produce indole. The 16S rRNA sequence of strain 6 was found to be most similar to that of som e Clostridium species, with homology ranging from 80 to 86%. The evolu tionary relationships of strain 6 to different groups of Clostridium a nd Clostridium-related species revealed that it does not emerge from a ny of these groups. Strain 6 most likely belongs to a new species clos ely related to Clostridium species.