Phylogeny ribosomal RNA gene typing and relative abundance of new Pseudomonas species (sensu stricto) isolated from two pinyon-juniper woodland soilsof the arid southwest US

Rhizosphere-inhabiting Pseudomonas species interact with plant roots and ma y be important for plant performance under stressful environmental conditio ns. A comparison was conducted of culturable Pseudomonas isolates associate d with pinyon rhizosphere and between-tree interspace areas in a hot, dry, volcanic cinder field and an adjacent sandy loam soil, in order to identify Pseudomonas species which may be involved in pinyon pine survival under st ressful conditions. From a collection of 800 isolates, eleven isolates exhi biting different colony morphology were selected for 16S ribosomal RNA gene sequencing. Phylogenetic analysis of rDNA sequences from the eleven field isolates, forty-six described Pseudomonas species, and thirty-four previous ly characterized environmental isolates indicated that the isolates from th e cinders and sandy loam soil clustered into three groups. The field isolat es were distinct from any of the named species or other environmental isola tes. Oligonucleotide primer pairs that differentiated three field isolate g roups were designed from the 16S rDNA sequences, and eight hundred Pseudomo nas field isolates cultured from pinyon rhizospheres and interspaces in the cinders and sandy loam soils were typed into the three groups using PCR as says. The composition of Pseudomonas populations in four environments was s ignificantly different. The relative abundance of the three rDNA-based grou ps appeared to be affected by both the soil type and the pinyon rhizosphere .