Spatio-temporal variations in the physiological profiles of streambed bacterial communities: implication of wastewater treatment plant effluents

The effluents of wastewater treatment plants (WWTPs) represent a complex mixture of nutrients and toxic substances, thus, the potential exists for the effluents to significantly impact the biochemical characteristics and bacterial communities of the receiving water. We examined spatial and seasonal patterns, and the impact of effluents on microbial biomass, bacterial community structure, and metabolic diversity on a fourth-order stream. We took triplicate sediment samples at five different locations along a 5000 m transect over three sampling periods. We quantified bacterial community structure as community-level physiological profiles and microbial biomass with phospholipid phosphate analysis. Our findings highlight the worrisome impacts of effluents on microbial biomass and bacterial metabolic diversity on the receiving water. Microbial biomass was significantly higher at the WWTP outfall compared to upstream and downstream sites and correlated positively with sediment physicochemical parameters. Furthermore, our data revealed significant spatial differences in bacterial community structure in the context of WWTP impact. High nutrient availability (lower carbon/nitrogen ratios) at the outfall increased site-specific bacterial metabolic diversity in winter but decreased the same in fall. Seasonal changes in the sedimentary microbial biomass and bacterial carbon substrate utilization were evident regardless of the spatial variations or impacts of the wastewater effluents. Communities in fall showed more versatile substrate utilization patterns than the winter communities. These results suggest that WWTP effluents significantly increased microbial biomass and highlight its mixed effects on bacterial community structure and metabolic diversity. Also, our data underscore a close association between sedimentary physicochemical parameters and the associated microbial functional activities.