Vibrio are a genus of marine bacteria that have substantial environmental and human health importance, and there is evidence that their impact may be increasing as a consequence of changing environmental conditions. We investigated the abundance and composition of the Vibrio community within the Sydney Harbour estuary, one of the most densely populated coastal areas in Australia, and a region currently experiencing rapidly changing environmental conditions. Using quantitative PCR (qPCR) and Vibrio-specific 16S rRNA amplicon sequencing approaches we observed significant spatial and seasonal variation in the abundance and composition of the Vibrio community. Total Vibrio spp. abundance, derived from qPCR analysis, was higher during the late summer than winter and within locations with mid-range salinity (5–26 ppt). In addition we targeted three clinically important pathogens: Vibrio cholerae, V. Vulnificus, and V. parahaemolyticus. While toxigenic strains of V. cholerae were not detected in any samples, non-toxigenic strains were detected in 71% of samples, spanning a salinity range of 0–37 ppt and were observed during both late summer and winter. In contrast, pathogenic V. vulnificus was only detected in 14% of samples, with its occurrence restricted to the late summer and a salinity range of 5–26 ppt. V. parahaemolyticus was not observed at any site or time point. A Vibrio-specific 16S rRNA amplicon sequencing approach revealed clear shifts in Vibrio community composition across sites and between seasons, with several Vibrio operational taxonomic units (OTUs) displaying marked spatial patterns and seasonal trends. Shifts in the composition of the Vibrio community between seasons were primarily driven by changes in temperature, salinity and NO2, while a range of factors including pH, salinity, dissolved oxygen (DO) and NOx (Nitrogen Oxides) explained the observed spatial variation. Our evidence for the presence of a spatiotemporally dynamic Vibrio community within Sydney Harbour is notable given the high levels of human use of this waterway, and the significant increases in seawater temperature predicted for this region.

The marine genus of bacteria, Vibrio, includes several significant human and animal pathogens, highlighting the importance of defining the factors that govern their occurrence in the environment. To determine what controls large-scale spatial patterns among this genus, we examined the abundance and diversity of Vibrio communities along a 4000 km latitudinal gradient spanning the Australian coast. We used a Vibrio-specific amplicon sequencing assay to define Vibrio community diversity, as well as quantitative PCR and digital droplet PCR to identify patterns in the abundances of the human pathogens V. cholera, V. parahaemolyticus and V. vulnificus. The hsp60 amplicon sequencing analysis revealed significant differences in the composition of tropical and temperate Vibrio communities. Over 50% of Vibrio species detected, including the human pathogens V. parahaemolyticus and V. vulnificus, displayed significant correlations with either temperature, salinity, or both, as well as different species of phytoplankton. High levels of V. parahaemolyticus and V. vulnificus were detected in the tropical site at Darwin and the subtropical Gold Coast site, along with high levels of V. parahaemolyticus at the subtropical Sydney site. This study has revealed the key ecological determinants and latitudinal patterns in the abundance and diversity of coastal Vibrio communities, including insights into the distribution of human pathogens, within a region experiencing significant ecological shifts due to climate change.

No abstract