Fragmented Shores Boost Antibiotic Threat in Crab Gut

Habitat fragmentation, the breaking up of continuous ecosystems into smaller pieces, can change how bacteria live inside animals. In tidal mudflats, a small crab species that is central to the food chain has become a useful eye on this process. Scientists examined how different landscape patterns affect the crab’s gut bacteria and the genes that make them resistant to antibiotics. The study combined maps of the mudflat, DNA sequencing from crab guts, and statistical models to trace connections. When the habitat was split into many small patches, crabs carried more antibiotic‑resistance genes (ARGs) and a larger variety of them. These crabs also showed higher amounts of mobile genetic elements (MGEs), the pieces of DNA that can move genes around, and more frequent pairing between ARGs and MGEs. This suggests that fragmentation makes it easier for resistance genes to spread.

Interestingly, fragmented areas also gave crabs a more varied diet. Yet, the gut bacterial communities were less different from one crab to another. The researchers think that the diet changes drive which bacteria settle in the gut, and those bacteria tend to carry more ARGs. The models pointed to a chain: diet changes gut microbes, which then acquire MGEs that bring ARGs. The chemistry of the mud itself did not play a big direct role. When looking deeper at which bacteria carried ARGs, two families stood out: Enterobacteriaceae and Vibrionaceae. These groups held most of the resistance genes, especially those that protect against many drugs or a specific drug called polymyxin. The findings highlight clear routes by which habitat changes can raise the risk of antibiotic resistance in a key species and suggest that protecting larger, connected mudflat areas could reduce this danger.

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