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Fish and shellfish pathogens of the Harveyi clade of the Vibrio genus cause significant losses to aquaculture yields and profits, with some of them also causing infections in humans. The present study aimed to evaluate the presence of Harveyi clade fish and shellfish pathogens and their possible diversification in response to environmental drivers in southeastern USA waters. The presence and abundance of potential pathogens were evaluated via the detection and quantitation of six Harveyi-clade-specific virulence genes (toxR, luxR, srp, vhha, vhh, and vhp; VGs) in environmental DNA with clade-specific primers. The environmental DNA was obtained from water and sediments collected from three Georgia (USA) cultured clam and wild oyster grounds. In sediments, the VG concentrations were, on average, three orders of magnitude higher than those in water. The most and least frequently detected VGs were vhp and toxR, respectively. In water, the VGs split into two groups based on their seasonal trends. The first group, composed of luxR, vhp, vhha, and vhh, peaked in August and remained at lower concentrations throughout the duration of the study. The second group, composed of toxR and srp, peaked in June and disappeared between July and December. The first group revealed a high adaptation of their carriers to an increase in temperature, tolerance to a wide range of pH, and a positive correlation with salinity up to 25 ppt. The second group of VGs demonstrated a lower adaptation of their carriers to temperature and negative correlations with pH, salinity, potential water density, conductivity, and dissolved solids but a positive correlation with turbidity. No such trends were observed in sediments. These data reveal the role of VGs in the adaptability of the Harveyi clade pathogens to environmental parameters, causing their diversification and possibly their stratification into different ecological niches due to changes in water temperature, acidity, salinity, and turbidity. This diversification and stratification may lead to further speciation and the emergence of new pathogens of this clade. Our data urge further monitoring of the presence and diversification of Harveyi clade pathogens in a global warming scenario. [ABSTRACT FROM AUTHOR]

In the face of global warming and ocean acidification, waterborne pathogens are geographically expanding and rapidly evolving. The Vibrio genus contains a number of pathogens of humans and aquatic animals, many of which benefit from elevated temperatures and low pH conditions. Vibrio harveyi and Vibrio campbellii belong to the Harveyi clade and are barely distinguishable upon their genetic make-up. Natively found in warm waters of Asia and South America, these species are well-established pathogens that infect fish, shrimp, and mollusks. Due to climate change, the Southeastern United States is potentially becoming an accommodating environment for these pathogens, however this has never been previously documented. In addition to using selective growth media for definitive pathogen detection, V. harveyi and V. campbellii-specific virulence genes, including toxR, luxR, vhh, vhh(a), srp, vhp, and rpoA, have been chosen for quantitative PCR analysis of environmental samples. Sediment and water were monitored for their presence and concentration at three sites around Townsend, GA. In summer 2022 monitoring, all seven genes were detected but their profiles and concentrations varied between sites, media, and sampling events. In water, toxR, luxR, srp, and rpoA were detected in 83% of the sites, and vhh(a), vhp, and vhh were detected in 100% with average gene copy concentrations from 10^2 to 10^8. In sediment, srp, vhh(a), and rpoA were detected in 83% of the sites and toxR, luxR, vhp, and vhh were detected in 100% of the sites with copy numbers from 10^1 to 10^9. These results evidenced that V. harveyi and V. campbellii inhabit Georgia coastal waters in high numbers. Additional data obtained in a supplemental study suggested their presence in oysters and clams. They also evidenced that not all previously published target genes are suitable for detection of these pathogens., Recommended Citation Authors Cameron Brown (*), Georgia College & State University, Milledgeville, GA 31061 Follow Alexandra Rosa-Calix (*), Georgia College & State University, Milledgeville, GA 31061 Follow Andrei L. Barkovskii, [...]