Abstract
Vibrio vulnificus is an opportunistic pathogen indigenous to estuarine and marine environments and associated with aquatic organisms. Vibrio vulnificus is of utmost importance because it causes 95% of the seafood-related deaths in the United States due to rapid progression of septicemia. Changes in environmental parameters associated with climate change and coastal population expansion are altering geographical constraints, resulting in increased Vibrio spread, exposure, and rates of infection. In addition, coastal population expansion is resulting in increased input of treated municipal sewage into areas that are also experiencing increased Vibrio proliferation. This study aimed to better understand the influence of treated sewage effluent on effluent-receiving microbial communities using Vibrio as a model of an opportunistic pathogen. Integrated transcriptomic approaches were used to analyze the changes in overall gene expression of V. vulnificus NBRC 15645 exposed to wastewater treatment plant (WWTP) effluent for a period of 6h using a modified seawater yeast extract media that contained 0, 50, and 100% filtered WWTP effluent. RNA-seq reads were mapped, annotated, and analyzed to identify differentially expressed genes using the Pathosystems Resource Integration Center analysis tool. The study revealed that V. vulnificus responds to wastewater effluent exposure by activating cyclic-di-GMP-influenced biofilm development. Also, genes involved in crucial functions, such as nitrogen metabolism and bacterial attachment, were upregulated depending on the presence of treated municipal sewage. This altered gene expression increased V. vulnificus growth and proliferation and enhanced genes and pathways involved in bacterial survival during the early stages of infection in a host. These factors represent a potential public health risk due to exposure to environmental reservoirs of potentially Vibrio strains with enhanced virulence profiles in coastal areas.
Highlights
Climate change, sea warming, and increasing ocean pollution have been recognized in the Human Health and Ocean Review (Landrigan et al, 2020) as contributing factors to increased frequency of Vibrio-illness and its spread into previously unaffected areas
To examine the effect of wastewater effluent on bacterial growth, V. vulnificus was grown at 25°C in 96 well plates containing four replicates of 150 μl of Modified Seawater Yeast Extract (MSYE; Oliver and Colwell, 1973) with 0% effluent (MSYE reconstituted with 100% DI water and no effluent), 50% effluent (MSYE reconstituted with 50% effluent and 50% DI water), and 100% effluent (MSYE reconstituted with 100% effluent and 0% DI water)
Vibrio spread and proliferation have been reported in coastal zones and with increased poleward movement (Baker-Austin et al, 2018; Deeb et al, 2018; Froelich and Daines, 2020)
Summary
Sea warming, and increasing ocean pollution have been recognized in the Human Health and Ocean Review (Landrigan et al, 2020) as contributing factors to increased frequency of Vibrio-illness and its spread into previously unaffected areas. An infection caused by Vibrio species, can present multiple clinical manifestations including gastroenteritis and wound infections that can develop further into acute septicemia in immunocompromised individuals. This opportunistic pathogen grows preferentially in warm aquatic environments (>18°C) with salinity ranging from approximately 5 to 25 ng/L NaCl. This opportunistic pathogen grows preferentially in warm aquatic environments (>18°C) with salinity ranging from approximately 5 to 25 ng/L NaCl These narrow growth parameters have historically acted as environmental constraints to the spread of Vibrio in natural ecosystems. The differentially expressed genes in these studies included genes involved in flagellar components, GGDEF family protein, iron acquisition system, bacterial toxins (RtxA1 and VvhA), and others
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