IDENTIFICATION OF VARIABILITY OF RIBOSOMAL DNA SPACER FROM PSEUDOMONAS SOIL ISOLATES

The polymerase chain reaction was used to amplify the spacer region lo cated between the 16S and 23S ribosomal RNA genes of strains of Pseudo monas fluorescens and Pseudomonas putida isolated from peat bog, canol a field, or arctic plants. Some of these amplified spacer regions were used to probe Southern blots of total DNA digests from the various st rains of P. fluorescens and P. putida. Differences were observed in th e patterns of hybridization of the various bacterial DNAs. The ribosom al DNA spacer region of four of the P. fluorescens strains examined, s trains 64-3, 63-28, QP5, and R17-FP2, was about 515 base pairs (bp) in length, and contained the genes for tRNA(Ile) and tRNA(Ala). The DNA sequences of two strains from canola, 64-3 and 63-28, differed at only two positions. The sequences of the peat bog strains QP5 and R17-FP2 were identical. However, differences were noted between the DNA sequen ce common to the pair of strains 64-3 and 63-28 and the corresponding common sequence for strains QP5 and R17-FP2. These differences were ma inly concentrated in two DNA segments of 10 and 19 bp, respectively. A probe for the 19-bp variable segment that occurs in the ribosomal Spa cer of strains QP5 and R17-FP2 recognized total DNA from these two str ains, but not DNA from other bacteria of different origins. These resu lts suggest the existence of a limited degree of variability within th e 16S-23S ribosomal DNA spacer region, and that this variability may b e useful to the recognition of particular Pseudomonas strains from env ironmental samples.