Biological and Ecological Studies on Bdellovibrio

1. Isolation, morphology, and parasitism of Bdellovibrio

Abstract

Six isolates of ectoparasitic bacteria having different host ranges were collected from paddy field soil and irrigation water in Japan, by using Xanthomonas oryzae, the pathogen of bacterial leaf blight of rice, as indicator.
The ectoparasitic bacteria produced plaques which resembled in appearance to those due to bacteriophages, 2 to 4 days after plating on the bacterial lawn. The plaques enlarged gradually showing somewhat irregular circumference, and finally covered the entire surface of the plates. The size of the plaques showed much variation. The average size seemed to differ according to incubation conditions, but not to isolates.
In any of the six isolates, a single plaque usually comprised two different type of cells. The Vibrio form cells were 0.75 to 1.87μ in length and 0.28 to 0.34μ in thickness, while spherical cells were 0.28 to 0.34μ in diameter. Each cell possessed a single thick polar flagellum.
The ectoparasitic bacteria attacked 5 to 30 species of Gram-negative bacteria out of 64 tested, but none of the tested Gram-positive or Gram-variable bacteria. All 45 tested isolates of X. oryzae were attacked by any of the six isolates.
The ectoparasitic bacteria were identified from their characteristics as Bdellovibrio bacteriovorus Stolp and Starr.