Phylogeny, Ribosomal RNA Gene Typing and Relative Abundance of New Pseudomonasspecies (sensu stricto)isolated from Two Pinyon-Juniper Woodland Soils of the Arid Southwest U.S.

Rhizosphere-inhabiting Pseudomonasspecies interact with plant roots and may be important for plant performance under stressful environmental conditions. A comparison was conducted of culturable Pseudomonasisolates associated 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 Pseudomonasspecies which may be involved in pinyon pine survival under stressful conditions. From a collection of 800 isolates, eleven isolates exhibiting different colony morphology were selected for 16S ribosomal RNA gene sequencing. Phylogenetic analysis of rDNA sequences from the eleven field isolates, forty-six described Pseudomonasspecies, and thirty-four previously characterized environmental isolates indicated that the isolates from the cinders and sandy loam soil clustered into three groups. The field isolates were distinct from any of the named species or other environmental isolates. Oligonucleotide primer pairs that differentiated three field isolate groups were designed from the 16S rDNA sequences, and eight hundred Pseudomonasfield isolates cultured from pinyon rhizospheres and interspaces in the cinders and sandy loam soils were typed into the three groups using PCR assays. The composition of Pseudomonaspopulations in four environments was significantly different. The relative abundance of the three rDNA-based groups appeared to be affected by both the soil type and the pinyon rhizosphere.