Response of the Predatory Bacterium, Halobacteriovorax, and Virus to an Influx of a Prey Bacterium in a Natural Water Microcosm and a Three Membered Artificial Sea Water Microcosm.

Halobacteriovorax (HBx) is a predatory bacterium that preys on Vibrio sp. and many other gram negative bacteria. There is strong evidence that suggest HBx has a role in bacterial mortality in marine and brackish systems. However, its role has not been appropriately explored. In this study the rate of HBx predation on Vibrio vulnificus in comparison to that of viruses has been investigated. Initial experiments compared the responses of HBx and viruses in estuarine water systems to an input of V. vulnificus. Environmental water samples were filtered to remove larger protists and other organisms and debris. The filtered samples were used to establish laboratory microcosms to which was added a suspension of V. vulnificus. To measure the responses of HBx and viruses to the influx of V. vulnificus, samples were removed at intervals over a 40 h incubation period to enumerate HBx and V. vulnificus by culture and viruses by direct microscopic counts. In a subsequent experiment we investigated the responses of a virus and HBx strain when cultured with a suspension of V. vulnificus in a laboratory controlled microcosm of artificial sea water. The results of both experiments revealed that HBx was the first and most rapid responder to the inoculum of V. vulnificus and reduced their numbers significantly. The viruses were relatively non-responsive and did not substantially reduce V. vulnifius numbers. These results show that HBx may be a major contributor to bacterial mortality in conjunction with protists and viruses