Abstract
Since plaque-forming efficiency (PFE) of Bdellovibrio isolate BdN6801 was found to vary depending upon the kinds and conditions of indicator bacteria used, the factors causing those variations were studied by using three kinds of bacteria, Erwinia carotovora, Xanthomonas oryzae and Enterobacter aerogenes.
When E. carotovora was used as an indicator, PFE of BdN6801 was markedly influenced by incubation temperature. High titer of PFE was observed on E. carotovora cultured at 20C and the titer was almost the same as that obtained with X. oryzae. Remarkable decrease in PFE was observed when E. carotovora grown at 30C was used. PFE of BdN6801 obtained with E. aerogenes was lower as compared with that with X. oryzae or E. carotovora even under the optimum conditions for plaque formation.
Bdellovibrio BdN6801 obtained from single plaque on X. oryzae was successively cultured on each of the three hosts mentioned above, and the variations in PFE and plaque appearance were examined. Remarkable variation in PFE was not observed in the case of successive transfers on X. oryzae. Conspicuous decrease in PFE was observed on the lawn of X. oryzae when BdN6801 was successively cultured on E. carotovora. When transferred back on X. oryzae, PFE estimated with X. oryzae almost recovered its original level, though plaques were somewhat obscure. On the other hand, when BdN6801 was successively transferred on E. aerogenes, no remarkable change in PFE was observed on the lawn of X. oryzae. However, it produced much clear plaques on the lawn of E. aerogenes as compared with the cells successively transferred on X. oryzae. The results indicate that the variations in PFE and in plaque appearance of Bdellovibrio possibly occur by successive transfers on a single host, and the PFE characterization is reversible.
