Connecting Thiamine Availability to the Microbial Community Composition in Chinook Salmon Spawning Habitats of the Sacramento River Basin

Abstract

Thiamine Deficiency Complex (TDC) is a major emerging threat to global populations of culturally and economically important populations of salmonids. Salmonid eggs and embryos can assimilate exogenous thiamine, and evidence suggests that microbial communities in benthic environments can produce substantial amounts of thiamine. We therefore hypothesize that microbially produced thiamine in both riverine surface water and hyporheic zones could serve to rescue early life stages of salmonids suffering from TDC. The distributions of thiamine and its metabolically related compounds (dTRCs) have never been determined in freshwater systems. Similarly, the microbial cycling of these compounds has never been investigated. Here we determine that all dTRCs are present in femto-picomolar concentrations across diverse salmon spawning habitats in California's Sacramento River system. We observed that thiamine concentrations in the Sacramento River are orders of magnitude lower than marine environments, indicating substantial differences in thiamine cycling between these two environments. Our data suggest that the hyporheic zone is likely the source of thiamine to the overlying surface water. Temporal variations in dTRC concentration were observed where highest concentrations were seen when Chinook salmon were actively spawning. Significant correlations were identified between the richness of differentially abundant ASVs and dTRC concentrations. The influence of these ASVs on dTRC concentrations provide evidence of dTRC cycling by microbes in the hyporheic zone, which would influence the conditions where embryonic salmon incubate. Together, these results indicate a connection between microbial communities in freshwater habitats and the availability of thiamine to spawning TDC-impacted California Central Valley Chinook salmon.