Temporal and spatial distribution of microbial community in urban river in Dhaka

Abstract

Buriganga River in central Bangladesh represents a complex ecosystem with extreme pollution and altered water quality. It is well known that microorganisms play a key role in regulating the function and health of aquatic ecosystems. Microbial activities also have a direct impact on biogeochemical cycling and degradation of pollutants. Despite numerous studies on the physicochemical parameters of the water quality of this central river, a comprehensive understanding of microbial diversity and the impact of water’s physicochemical properties on bacterial community structure is not well documented. Therefore, the present investigation was done to elucidate the spatial and temporal shifts of microbial communities in the Buriganga River water in correlation to different physicochemical factors as well as heavy metal content. A total of 13 distinct sampling sites (from Amin Bazar Bridge to Postogola Cantonment B-C Friendship Bridge) encompassing a length of approximately 19 km along the river’s centre were selected to gather the sample seasonally during pre-monsoon, monsoon, post-monsoon, and winter. 16S rRNA gene-based metagenomics analysis revealed significant variation of bacterial diversity in winter rather than the rest of the three seasons with minimal variation suggesting stable geochemical cycles. Also, microbial diversity was higher at sampling points downstream compared to upstream along the river with overall dominance ofProteobacteriaandFirmicutes. Physicochemical water quality parameters analysis identified Zn, TP (Total phosphate), BOD, and COD as key factors influencing bacterial community diversity and composition, although they were not the sole contributors. At the heavily polluted Lohar Bridge (10CS) site, significant nitrogen cycle disruption was evident. The high abundance of metal and antibiotic-resistant bacteria genera such asPseudomonas,Ralstonia, andAcinetobacterat specific sampling positions indicated a relation between antibiotic and heavy metal pollution from adjacent hospitals and industrial effluent release points. The prevalence of metabolically unique bacteria such asGeobacterandDehalococcoides, that are well known for utilizing specific heavy metals like iron and uranium as well as chlorinated compounds, might indicate the selective pressure of metal pollution from nearby working factories/industries. The investigation also identified potential pathogens likeArcobacter, Acinetobacter,andPseudomonas,posing potential risks to both the environment and human health. Therefore, the Buriganga River belt serves as a potential hub for metal-antibiotic tolerant/resistant species with a direct influence on indigenous river-flowing communities correlating unique nutrient/geochemical cycling. The overall microbial community reflects unrestricted pollution in Buriganga central river aggravating water quality for regular use, indicating urgent intervention.GRAPHICAL ABSTRACTHIGHLIGHTSignificant bacterial diversity was observed during winter compared to the other three seasons (Premonsoon, monsoon, and post monsoon).Zn, TP, BOD, and COD were found to be key factors influencing the diversity and composition of the bacterial community.Disruption of the nitrogen cycle was evident at the heavily polluted monitoring point.Potential pathogens were identified that may pose risks to both the environment and human health.