Effects of temperature and salinity on Vibrio vulnificus population dynamics as assessed by quantitative PCR

Abstract

The abundance of Vibrio vulnificus in coastal environments has been linked to water temperature, while its relationship to salinity is less clear. We have developed a culture-independent, most-probable-number quantitative PCR approach to examine V. vulnificus population dynamics in Barnegat Bay, N.J. Based on the combined analysis of our results from Barnegat Bay and from the literature, the present data show that (i) V. vulnificus population dynamics are strongly correlated to water temperature and (ii) although the general trend is for V. vulnificus abundance to be inversely correlated with salinity, this relationship depends on salinity levels. Irrespective of temperature, high abundances of V. vulnificus are observed at 5 to 10 ppt, which thus appears to be the optimal salinity regime for their survival. At 20 to 25 ppt, V. vulnificus abundances show a positive correlation to salinity. Unsuccessful attempts to resuscitate V. vulnificus, combined with our inability to detect cells during the winter despite an assay adapted to detect viable but nonculturable (VBNC) cells, suggest that the decline and eventual disappearance of V. vulnificus from the water column during the winter months is due primarily to a significant reduction in population size and is not only the consequence of cells entering the VBNC state. These findings are in line with the hypothesis that the sediment serves as a refuge for a subpopulation of V. vulnificus over the winter and weather-driven mixing events during the spring initiate a summer bloom in the water column.

FIG. 1.

Seasonal fluctuations of temperature, salinity, and chlorophyll a (A) and total bacteria and V. vulnificus abundance (B) in Barnegat Bay, N.J. Open bars indicate sampling dates on which V. vulnificus was not detected.

FIG. 2.

Relationship between V. vulnificus abundance and temperature in Barnegat Bay from June 2001 to February 2003. For linear regression analysis, the limit of detection (1 cell ml⁻¹) was used for samples in which V. vulnificus was not detected.

FIG. 3.

Relationship between the summer abundances of V. vulnificus and salinity in Barnegat Bay (June 21 to September 21 of 2001 and 2002).

FIG. 4.

V. vulnificus abundance as a function of temperature and salinity. The data was compiled from this study and the studies summarized in Table 1. Only abundances that are >1 cell ml⁻¹ are plotted on this graph. The sizes of the bubbles are proportional to the relative abundance of V. vulnificus, which is grouped into nine categories: 1 to 50, 51 to 100, 101 to 250, 251 to 500, 501 to 750, 751 to 1,000, 1,001 to 2,500, 2,501 to 5,000, and >5,000 cells ml⁻¹.