Stenotrophomonas rhizophila sp. nov., a novel plant-associated bacterium with antifungal properties.

A polyphasic taxonomic study was performed on 16 Stenotrophomonas strains from environmental and clinical sources. A group of three plant-associated isolates were shown to be phenotypically different from the other strains. This group formed a separate physiological cluster (B1) with 42% heterogeneity to the other isolates. The defining characteristics of the new species were as follows: growth at 4 degrees C and the absence of growth at 40 degrees C; the utilization of xylose as a carbon source; lower osmolytic tolerance (< 4.5% NaCl, w/v), although the isolates can produce trehalose and glucosylglycerol as osmoprotective substances; the absence of lipase and beta-glucosidase production; and antifungal activity against plant-pathogenic fungi. The whole-cell fatty acid profile of this group was different and characterized by the main fatty acids iso-C15:0 and anteiso-C15:0. Numerical analysis of the fatty acid profiles of the strains examined supports the differentiation of the physiological B1 group. By 16S rDNA analysis, three clusters were distinguished. The three strains of the B1 group formed a separate environmental cluster (E1). They showed a mean similarity of 99.5% within the cluster, and differed from strains of a second environmental cluster (E2) by 2.2% and from the clinical cluster (C) by about 3.0%. DNA-DNA hybridization data supported the taxonomic differentiation. All results led to the proposal of a new species, Stenotrophomonas rhizophila sp. nov., with strain e-p10(T) (= DSM 14405(T) = ATCC BAA-473(T)) as the type strain.