Avian Species Driven Cultivable Bacterial Community from the Coastal Ecosystem of Gujarat, India

Abstract

Background: Coastal birds are particularly interesting models for microbiome research because they rely on dynamic interface ecosystems in which terrestrial, freshwater, and marine influences converge. Aim: The study aims to investigate the factors shaping culturable bacterial communities associated with coastal birds and determine the relative influence of host species identity versus environmental filtering along the Gujarat coast. Study Design: A cross-sectional observational study was conducted to examine bacterial communities in 12 coastal bird species across four distinct habitat types. Place and Duration of the Study: Four coastal sites in Gujarat, India: Bhavnagar (industrial mudflats), Hathab (sandy beach), Mithi Virdi (estuarine mangroves), and Cabel Bridge (tidal creek salt marsh). Sampling was conducted during high-tide periods and from injured birds rescued during "Karuna Abhiyan". Methodology: Fecal, tracheal, and cloacal swabs were collected from 12 coastal bird species. Bacteria were cultured on Zobell Marine agar, EMB, and MacConkey agar under aerobic conditions at 37°C. Isolates were identified using 16S rRNA gene sequencing and BLAST analysis. Phylogenetic reconstruction was performed using maximum likelihood. Community analyses included PERMANOVA, beta diversity, indicator species analysis, SIMPER, variation partitioning, and CCA using Jaccard dissimilarity matrices. Results: Fifty-seven isolates represented 29 species across 17 genera, dominated by Firmicutes (70.2%), Proteobacteria (15.8%), and Actinobacteria (14.0%). PERMANOVA revealed host species identity as the primary factor structuring communities, explaining 24.0% of the variation (p=0.001), whereas site and compartment effects were not significant. Beta diversity was significantly higher between than within species (p=0.0011). Indicator analysis identified six significant associations after correction: Priestia megaterium with shorebirds (p-adjusted=0.012), Mammaliicoccus sciuri with pond heron (p-adjusted=0.015), Cytobacillus firmus with crab plover (p-adjusted=0.028), and halophilic taxa (Salinicoccus roseus, Citricoccus massiliensis) with gulls (p-adjusted=0.021-0.023). Environmental parameters showed no relationship with community composition (CCA p=0.481). Variation partitioning confirmed that host species contributed the largest unique fraction (8.7%). Conclusion: Host ecological identity, mediated by foraging guilds and behavioral niches, is the primary determinant of culturable bacterial communities in coastal birds. The detection of potentially opportunistic taxa underscores the role of birds as reservoirs within the OneHealth framework. This study establishes a critical baseline for avian microbiomes in biodiverse coastal regions.