Fermentative bacteria from estuarine mud: phylogenetic position of Acidaminobacter hydrogenoformans and description of a new type of gram-negative, propionigenic bacterium as Propionibacter pelophilus gen. nov., sp. nov.

The phylogenetic positions of two strains of fermentative bacteria that had been isolated from the highest positive tubes inoculated with serial dilutions of estuarine mud in agar media with either glutamate or aspartate as substrate were determined by comparative sequence analysis of their 16S rRNA genes. The strain isolated with glutamate (glu 65) utilized several substrates, including a number of amino acids but no sugars. The degradation of certain substrates was enhanced by or dependent upon co-cultivation with a hydrogen-utilizing partner. In earlier work this strain was assigned to the new genus and species Acidaminobacter hydrogenoformans. On the basis of its 16S rRNA gene sequence Acidaminobacter hydrogenoformans has now been identified as a member of cluster XI of the Clostridium subphylum with Clostridium halophilum as its closest relative. The aspartate-fermenting strain asp 66T was a Gram-negative, rather aerotolerant anaerobe which utilized a wide range of substrates in a propionic fermentation and had the ability to fix molecular nitrogen. Strain asp 66T was shown to be a new member of the beta-subclass of the Proteobacteria with Azoarcus sp. strain 6a3 and Rhodocyclus tenuis as its closest relatives. It is described as Propionibacter pelophilus gen. nov., sp. nov., with the type strain asp 66T (= DSM 12018T).