Prey range characterization, ribotyping, and diversity of soil and rhizosphere Bdellovibrio spp. isolated on phytopathogenic bacteria

Thirty new Bdellovibrio strains were isolated from an agricultural soil and from the rhizosphere of plants grown in that soil, Using a combined molecu lar and culture-based approach, we found that the soil bdellovibrios includ ed subpopulations of organisms that differed from rhizosphere bdellovibrios , Thirteen soil and seven common bean rhizosphere Bdellovibrio strains were isolated when Pseudomonas corrugata was used as prey; seven and two soil s trains were isolated when Erwinia carotovora subsp, carotovora and Agrobact erium tumefaciens, respectively, were used as prey; and one tomato rhizosph ere strain was isolated when A. tumefaciens was used as prey. In soil and i n the rhizosphere, depending on the prey cells used, the concentrations of bdellovibrios were between 3 x 10(2) to 6 x 10(3) and 2.8 x 10(2) to 2.3 x 10(4) PFU g(-1). A prey range analysis of five soil and rhizosphere Bdellov ibrio isolates performed with 22 substrate species, most of which were plan t-pathogenic and plant growth-enhancing bacteria, revealed unique utilizati on patterns and differences between closely related prey cells. An approxim ately 830-bp fragment of the 16S rRNA genes of all of the Bdellovibrio stra ins used was obtained by PCR amplification by using a Bdellovibrio-specific primer combination, Soil and common bean rhizosphere strains produced two and one restriction patterns for this PCR product, respectively. The 16S rR NA genes of three soil isolates and three root-associated isolates were seq uenced. One soil isolate belonged to the Bdellovibrio stolpii-Bdellovibrio starrii clade, while all of the other isolates clustered with Bdellovibrio bacteriovorus and formed two distantly related, heterogeneous groups.