Fish as a winter reservoir for Vibrio spp. in the southern Baltic Sea coast

Abstract

Vibrio spp. are ubiquitous in aquatic environments. In temperate regions, including the Baltic Sea, these bacteria, which include facultative pathogenic species, proliferate during warm water periods and may thus pose a risk to human health. However, while present at relatively high abundances in the summer months, Vibrio spp. are rarely detected during cold water periods. Several potential winter reservoirs, such as fish and sediment, have been discussed, but the seeding sources that give rise to Vibrio during the summer months are unknown. In this study, we employed a combination of cultivation-independent genus-specific digital droplet PCR, Illumina 16S rRNA gene sequencing, culture-dependent determinations of colony-forming units (CFU) and genus-specific strain isolation to identify possible winter reservoirs of Vibrio spp. Using these techniques, we demonstrate that in the southern Baltic Sea especially fish can serve as a winter reservoir for distinct Vibrio assemblages, including facultative pathogenic V. vulnificus . Particularly the invasive species round goby ( Neogobius melanostomus ), with its potential to appear in high individual densities, has the capacity to carry a comparable Vibrio spp. cell number like water and sediment, while only accounting for 1/1000 of the spatial share in the overall coastal environment. Thus, by providing a winter reservoir for distinct Vibrio communities, coastal fish and, especially areas in which round goby densities are high, may be hot spots of pathogenic Vibrio species. • Fish acts as Vibrio winter reservoir in the Baltic Sea. • Vibrio spp. often highest abundant in connection to invasive species round goby. • Quantitative Vibrio 16S rRNA gene ddPCR without Photobacterium falsification.