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Reclassification of salt-water Bdellovibrio sp. as Bacteriovorax marinus sp. nov. and Bacteriovorax litoralis sp. nov.

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Recent studies suggest that surfaces are a more conducive habitat than the water column for the proliferation of bdellovibrios in the aquatic environment. The effect of temperature and salinity on the colonization of bdellovibrios on oyster shell, glass, and polystyrene surfaces in situ was investigated over an annual cycle. Sterile surfaces were suspended in various bodies of water for intervals ranging from 24 to 120 h. The results revealed that bdellovibrios associated with different types of surfaces over a broad temperature and salinity range. After 24 h of submersion in waters with temperatures from 9.0 to 26.7؇C, the ranges in log 10 values per square centimeter for the three surfaces were as follows: oyster shell, 2.2 to 2.5; glass, 0.3 to 2.2; and polystyrene, 0.7 to 1.6. Bdellovibrios were not recovered from surfaces submerged in water at temperatures below 8؇C during the 120-h experimental cycle. The number of bdellovibrios and culturable bacteria on oyster shells was significantly higher than the numbers on glass and polystyrene at all time intervals. The number of bdellovibrios was positively correlated with temperature and salinity on all surfaces. A positive correlation between the number of recoverable bacteria and temperature was observed, but the results with respect to salinity were diverse. The numbers of bdellovibrios recovered from oyster shells (up to 48 h) and water samples were significantly increased at salinities greater than 11‰ compared to those in lower-salinity environments. The results of this study reveal that like many other bacteria in the aquatic environment, bdellovibrios prefer to associate with surfaces. This association provides the predators a rich source of prey bacteria in surface biofilms and perhaps protection in the gel-like matrix of the biofilm. Bdellovibrio bacteriovorus is a small (0.2-m), commashaped, gram-negative, predatory procaryote which obligately preys on many gram-negative bacteria (6, 16, 17, 21). The characteristic lethal attack by bdellovibrios on prey bacteria has generated interest in its impact on bacterial mortality in nature and its potential as a biological control agent. However, the low numbers of bdellovibrios typically recovered from the water column and sediment (25, 27), the sites most often studied, have established some doubt about the influence of the predators on populations of bacteria in the aquatic environment. In response, it has been suggested that both the number and activity of the bdellovibrios may be higher in habitats other than bulk water and sediments (13). Recent studies have revealed that greater numbers of the predators occur at the air-water and solid-water interfaces (24, 29). Surface colonization may be an important strategy in the ecology (28) of the bdellovibrios and an important mechanism of their survival in the aquatic environment, especially oligotrophic waters. The surface biofilm matrix offers these predators large numbers of potential prey bacteria and perhaps some protection from environmental forces, thus ma...

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