Unraveling the role of bacterial communities in mangrove habitats under the urban influence, using a next-generation sequencing approach

Mangrove ecosystems are vital coastal habitats with rich biodiversity and play a significant role in carbon sequestration, these habitats are facing mounting threats from rapid urbanization. This study delves into assessing the sediment bacterial communities from the urban mangrove habitats of Campal and Panaji, within the Mandovi estuarine environment of Goa, to understand the intricate interplay between urbanization and bacterial dynamics in the mangrove habitats. We used a combined approach of 16S amplicon and shotgun sequencing methodologies to understand the bacterial taxonomic composition and functional profiles. The community structure revealed the dominance of bacterial groups from phylum Proteobacteria, Chloroflexi and Actinobacteria at both locations. The impact of urbanization was evident from the increased abundance of pathogenic groups at class and genus levels in this region. The core microbiome analysis showed the presence of Shewanella, Pseudomonas and Clostridium which are mostly pathogenic, anaerobic taxa Woeseia, Rheinheimera, like genera that are involved in the organic matter cycling and unclassified bacteria. Though increased pathogenic forms are reported, it is evident that the dominant taxa also included groups that contributed to the biogeochemical cycling of organic matter in sediment from these locations. Functional diversity elucidated through shotgun metagenomics analysis showcased the predominance of carbohydrate metabolism and the presence of glycoside hydrolases degrading plant-based starch, pectin and cellulosic organic matter. The occurrence of xenobiotic biodegradation pathways is an indication of the presence of xenobiotic degrading microbes as a natural means of degrading high amounts of pollutants at this location. Comparative analysis of the metagenomes from this study with similar earlier studies at Ribandar, Mandovi and Cortalim, Zuari mangrove habitats of Goa with varying pollution levels also reiterates the terrestrial influence on the microbial community in these habitats. It showed that Panaji and Campal locations had the presence of dominant pathogenic forms which was absent in the other two locations. The Ribandar and Coratlim location which is reported to have a comparatively lesser impact due to anthropogenic activity had an increased abundance of distinct genera which are predominant heterotrophic forms involved in remineralization and reduced levels of pathogens. Our findings highlight the profound influence of urbanization on the sediment mangrove bacterial communities and spotlight the resilience and adaptability of these microorganisms. This calls for immediate action and preventive measures to restore their functional potential in maintaining the health of these ecosystems amidst expanding urban landscapes.