Numerical taxonomic study of three N2-fixing yellow-pigmented bacteria related to Pseudomonas paucimobilis

Three N2-fixing yellow bacteria (5AJ, 5ATR, and 29AJ) isolated from the rhizosphere of rice, previously found to be related to Flavobacterium capsulatum by DNA–rRNA hybridization, were compared on the basis of 115 morphological, physiological, biochemical, and nutritional characters. The bacteria were nonfermentative, irregular motile rods with polar flagella. They exhibited a gram-negative reaction and yellow pigmentation. A numerical analysis using these phenotypic characteristics showed that the bacteria were more closely related to Pseudomonas paucimobilis than to F. capsulatum. A relationship to the P. paucimobilis cluster was also supported by the presence of the pigment nostoxanthin. This pigment was also found in F. capsulatum and could be used as a distinctive marker for this group of yellow bacteria. Their phenotypic properties, protein patterns, and serological tests (ELISA) showed that two of the isolates (5AJ and 5ATR) were identical and had originated from the same parental strain. On the other hand, the serological tests indicated that both N2-fixing yellow bacteria (5AJ or 5ATR and 29AJ) differed from the reference strains, F. capsulatum and P. paucimobilis. Key words: N2-fixing bacteria, taxonomic study, nostoxanthin, Pseudomonas.