SUSCEPTIBILITY OF BACTERIA IN ESTUARINE ENVIRONMENTS TO AUTOCHTHONOUSBDELLOVIBRIOS

Members of the genus Bdellovibrio exist as obligate predators of other gram-negative bacilli. They are believed to require large numbers of prey bacteria (>10(4) ml(-1)) to survive. Although prey bacteria are e ssential to the survival of bdellovibrio populations, and to studies o f the predator's role in nature, the number of bdellovibrio-susceptibl e bacteria in environmental samples has not been investigated. This st udy quantified bacteria that were susceptible to predation by the bdel lovibrios. Bacteria recovered from water, sediment, and oyster-shell s urface epibiota at various sites in the Chesapeake Bay system were tes ted for their susceptibility to bdellovibrios collected from homologou s sites. The mean number (log(10)) of susceptible bacterial colonies r ecovered 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 isola tes tested were susceptible to bdellovibrios. Considering the actual n umber of bacteria in most environments is estimated to be 100 to 1000- fold greater than measured by culturing, the number of bdellovibrio-su sceptible bacteria in the three environments sampled is probably suffi cient to support the growth of the bdellovibrios.