Abstract
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.
Highlights
Marine microbes play essential ecological and biogeochemical roles in coastal and estuarine habitats (Ducklow and Carlson, 1992), but some species pose a significant threat to ecosystem function and human health
Salinity decreased across the estuary from the two most eastern sites at Chowder Bay and Mort Bay, where salinities were near to marine conditions, to the western sites including Olympic Park, Rhodes, and Parramatta Park, where salinity dropped to 0–14.1 ppt
Our study revealed that Vibrios, including several human pathogens, are an abundant and dynamic component within the Sydney Harbour estuary, and that the community displays marked spatiotemporal heterogeneity that can often be clearly linked to environmental variables including temperature
Summary
Marine microbes play essential ecological and biogeochemical roles in coastal and estuarine habitats (Ducklow and Carlson, 1992), but some species pose a significant threat to ecosystem function and human health. As an important natural component of bacterioplankton communities they contribute to biogeochemical cycling in aquatic habitats (Eiler et al, 2006; Thompson and Polz, 2006; Hasan et al, 2015) Due to their potentially significant impact on coastal ecosystems, marine animals, aquaculture (Higgins, 2000; Kushmaro et al, 2001; Ben-Haim and Rosenberg, 2002; Zorrilla et al, 2003; Austin and Zhang, 2006; Geng et al, 2014; Vezzulli et al, 2015) and human health (Daniels and Shafaie, 2000; Baker-Austin et al, 2013; Orata et al, 2014) an understanding of the spatiotemporal dynamics of Vibrios and their potential to bloom and cause disease outbreaks has become increasingly important (Lipp et al, 2002; Oberbeckmann et al, 2012; Takemura et al, 2014). This is true in light of recent evidence that this group of organisms are increasing in abundance and impact in some regions as a consequence of environmental perturbations and climate change (Oberbeckmann et al, 2012; Froelich et al, 2013; Jacobs et al, 2014; Takemura et al, 2014)
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