The plant growth-promoting rhizobacterium Pseudomonas sp. GR12-2 is closely related to the Pseudomonas syringae group of plant pathogens: phylogenetics, ecology, and plasmid biology.

摘要

Pseudomonas putida GR12-2 is a well known plant growth-promoting rhizobacterium (PGPR); however, 16S rRNA gene sequence analysis showed that this strain shared 99% sequence identity with the Pseudomonas syringae complex, which is composed of plant pathogens. A phylogenetic analysis of the Pseudomonas group using a multi-locus sequence typing (MLST) protocol of four housekeeping genes showed that the GR12-2 strain and the P. syringae complex form a monophyletic group. A fine scale phylogenetic analysis using the gyrB gene confirmed this result. On the basis of these sequence analyses we suggest that P. putida GR12-2 be re-designated Pseudomonas sp. GR12-2. To compare the ecological roles of Pseudomonas sp. GR12-2 with its close relatives, P. syringae pathovar (pv.) tomato DC3000 and P. syringae pv. syringae B728a, we investigated their ability to cause disease and promote plant growth. When introduced on tobacco or tomato leaves, Pseudomonas sp. GR12-2 was unable to elicit a hypersensitive response or cause disease, which are characteristic responses of P. syringae DC3000 and B728a, nor were type III secretion system genes required for virulence detected in Pseudomonas sp. GR12-2 by PCR or DNA hybridization. In contrast to Pseudomonas sp. GR12-2, neither of the phytopathogens was able to promote root growth when inoculated onto canola seeds. Finally, to compare the role of the native plasmid of Pseudomonas sp. GR12-2 with the native plasmids of P. syringae , we attempted to cure the strain of its plasmid.