Evaluating the Impact of Environmental Factors on Bacterial Populations in Riverine, Estuarine, and Coastal Sediments

Aquatic ecosystems, including rivers, estuaries, and coastal environments, are crucial for maintaining biodiversity, regulating nutrient cycles, and supporting human livelihoods. However, these ecosystems are increasingly being threatened by urbanization, making it essential to understand their microbial communities and their ecological roles. This study employed high-throughput 16S rRNA gene sequencing to characterize the bacterial communities within the riverine, estuarine, and coastal sediments of Adyar Creek, Chennai, India. Proteobacteria were the dominant phylum across most samples, with proportions ranging from 39.65% to 72.09%. Notably, the estuarine environment exhibited a distinct taxonomic profile characterized by a significant abundance of Firmicutes (47.09% of the bacterial population). Distinct bacterial classes were observed across sediment types: Alphaproteobacteria (30.07–34.32%) in riverine sediments, Bacilli dominated estuarine sediments (40.17%), and Gammaproteobacteria (15.71–51.94%) in coastal sediments. The most significant environmental factors influencing the bacterial community composition across these samples were pH, salinity, phosphate, and nitrate. LEfSe (Linear discriminant analysis Effect Size) analysis identified specific genera within the estuary, including Bacillus (20.26%), unclassified_Paenibacillus (12.87%), Clostridium (3.81%), Gailella (3.17%), Paenibacillus (3.02%), Massilia (1.70%), Paraburkholderia (1.42%), and Pantoea (1.15%), as potential biomarkers for habitat health. Functional analysis revealed an elevated expression of the genes associated with ABC transporters and carbon metabolism in the estuary, suggesting a heightened nutrient cycling capacity. Furthermore, co-occurrence network analysis indicated that bacterial communities exhibit a strong modular structure with complex species interactions across the three sediment types. These findings highlight bacterial communities’ critical role and the key drivers in estuarine ecosystems, establishing a baseline for further investigations into the functional ecology of these vulnerable ecosystems.