The rice inoculant strain Alcaligenes faecalis A15 is a nitrogen-fixing Pseudomonas stutzeri

The taxonomic position of the nitrogen-fixing rice isolate A15, previously classified as Alcaligenes faecalis, was reinvestigated. On the basis of its small subunit ribosomal RNA (16S rRNA) sequence this strain identifies as Pseudomonas stutzeri. Phenotyping and fatty acid profiling confirm this res ult. DNA:DNA hybridisations, using the optical renaturation rate method, be tween strain A15 and Pseudomonas stutzeri LMG 11199(T) revealed a mean DNA- binding of 77%. The identification was further corroborated by comparative sequence analysis of the oprF gene, which encodes the major outer membrane protein of: rRNA homology group I pseudomonads. Furthermore we determined t he nifH sequence of this strain and of two putative diazotrophic Pseudomona s spp. and made a comparative analysis with sequences of other diazotrophs. These Pseudomonas NIM sequences cluster with NifH sequences isolated from the rice rhizosphere by PCR and of proteobacteria from the beta and gamma s ubclasses.