Host Gut Acts as a Refuge for Aquatic Microorganisms by Facilitating Microbial Diversity Recovery in Aquatic...

Environmental stressors can reduce microbial diversity in a single habitat; however, whether regional microbial diversity is maintained through dispersal across heterogeneous habitats remains largely unknown. Here, we provide experimental evidence that the host gut (mud crab, Scylla paramamosain) serves as a microbial refuge for aquatic bacteria under arsenic (As) stress, a novel mechanism for maintaining regional microbial diversity. Under a gradient of As stress, although bacterial abundance in water decreased by 15% to 49%, 50% to 85% of these bacteria spread into the host gut, maintaining relatively stable total bacterial numbers across both habitats. Community assembly of the spread taxa was increasingly governed by deterministic processes, highlighting the key role of environmental stress and the host in structuring "refugee bacterial community". Experimental validation using isolated aquatic bacteria further confirmed their spread into the host gut under As stress and subsequent release back into the aquatic environment after the host was transferred to a stress-free system, while most microorganisms were directly eliminated from the water in the absence of hosts under As stress, thereby demonstrating that environmental microbial communities can spread and colonize within host organisms under polluted conditions. This study reveals a novel microbial adaptation strategy wherein the host gut serves as an environmental microbial refuge under environmental stress and facilitates regional bacterial community recovery in the aquatic environment.