The role of temperature, salinity, and protozoan predation on the population dynamics of Vibrio vulnificus in Barnegat Bay, New Jersey

The goal of the present work was to expand our understanding of the abiotic and biotic mechanisms controlling the population dynamics of Vibrio vulnificus, an opportunistic human pathogen ubiquitous to estuarine environments. The current body of work has refined previous findings on parameters controlling V. vulnificus population dynamics. First, using a quantitative PCR approach, we confirmed that temperature is a strong determinant of V. vulnificus population dynamics in coastal waters and that the disappearance of V. vulnificus from the water column during winter months is due to a reduction of V. vulnificus abundance and not the sole consequence of cells entering the viable but nonculturable (VBNC) state. Second, we established that bacteria present in the VBNC state can be utilized as a food source by two representative protozoa species. Both protozoan species were capable of capturing, ingesting, and digesting VBNC V. vulnificus efficiently. Our study has laid the foundation for future studies addressing whether the VBNC state can be used as a response to grazing and whether bacteria can be stimulated to enter the VBNC state in the presence of grazers. Finally, we expanded on previous uses of bromodeoxyuridine (BrdU) to detect and isolate DNA from grazers that have incorporated BrdU from pre-labeled V. vulnificus. In culture-based studies, we tested the feasibility of the BrdU method to effectively label protozoan grazers using pre-labeled V. vulnificus cells as a tracer and two species of protozoa as bacterivores. Both species of protozoa ingested labeled V. vulnificus prey and incorporated BrdU into their DNA, and the bacterivory rates of the two protozoa were accurately measured by the BrdU method within the first 8 hours of the experiment. BrdU uptake experiments using environmental water samples revealed that the protozoa species responsible for grazing and controlling the abundance of V. vulnificus were very similar to the protozoa that were responsible for grazing on all bacteria, indicating that V. vulnificus is a quality food source for a wide range of predators. Our findings suggest that V. vulnificus populations are kept in check in coastal environments by counterbalancing their rapid growth response to changing environmental conditions with a high grazing mortality.