Bacterial diversity in the freshwater sponges of Sundarban and their potential role in biomonitoring toxic element pollution.

Sponges serve as the natural cleaner in diverse aquatic ecosystems, harboring diverse microbial communities and forming a highly specialized holobiont. The present study provides the first insights into the bacterial communities associated with freshwater sponges of Sundarban, highlighting their distinct microbial community composition compared to the surrounding water using 16S rRNA gene-based metataxonomic analyses. The analysis encompassing six sponge species collected from Sagar Island and Ghoramara revealed distinct variations in microbial abundance and diversity compared to their ambient water, suggesting selective bacterial associations with the sponges. The sponge species displayed a varied abundance of bacterial taxa across different species and locations. Furthermore, significantly greater concentrations of potentially toxic elements (PTEs) were observed in sponges when compared with corresponding water samples, thereby suggesting the bioaccumulation capability of these sponges. Functional profiling of bacterial communities in sponge and water samples revealed enrichment of various metabolic pathways linked to metal ion transport and resistance, as well as antimicrobial resistance in the sponges, suggesting an adaptive response to environmental stressors. The abundance of diverse metal ion regulators and transporters underscores the ecologically significant function of sponge-associated bacterial communities in metal ion resistance, placing the sponges as promising bioindicators for monitoring polluted aquatic ecosystems.IMPORTANCEFreshwater sponges play an essential role as natural biofilters in aquatic ecosystems, effectively purifying water. These sponges harbor unique microbial communities, forming a holobiont that is key to their ecological function. This study offers new insights into the bacterial communities associated with freshwater sponges from the Sundarbans, a previously underexplored region. Using 16S rRNA gene-based metataxonomic analyses, we compared the bacterial diversity of six sponge species from Sagar Island and Ghoramara to that of surrounding water. Our results reveal distinct bacterial associations within sponges, different from the ambient water's microbial composition. Notably, sponge concentrations of potentially toxic elements (PTEs) were much higher than in the surrounding water, highlighting their bioaccumulation capacity. Functional profiling of sponge-associated bacteria revealed genes related to metal ion transport and antimicrobial resistance, suggesting adaptive responses to environmental stress. This research enhances our understanding of sponge microbiomes and their potential for bioremediation, particularly for removing heavy metals from polluted water.