Susceptibility of Bacteria in Estuarine Environments to Autochthonous Bdellovibrios

Abstract

Members of the genus Bdellovibrio exist as obligate predators of other gram-negative bacilli. They are believed to require large numbers of prey bacteria (>10⁴ ml⁻¹) to survive. Although prey bacteria are essential to the survival of bdellovibrio populations, and to studies of the predator's role in nature, the number of bdellovibrio-susceptible bacteria in environmental samples has not been investigated. This study quantified bacteria that were susceptible to predation by the bdellovibrios. Bacteria recovered from water, sediment, and oyster-shell surface epibiota at various sites in the Chesapeake Bay system were tested for their susceptibility to bdellovibrios collected from homologous sites. The mean number (log₁₀) of susceptible bacterial colonies recovered by culture was 3.33 ml⁻¹ in water, 4.14 ml⁻¹ in sediment and 5.76 ml⁻¹ from oyster shells. Seventy three to 85% of all isolates tested were susceptible to bdellovibrios. Considering the actual number of bacteria in most environments is estimated to be 100 to 1000-fold greater than measured by culturing, the number of bdellovibrio-susceptible bacteria in the three environments sampled is probably sufficient to support the growth of the bdellovibrios.