Mass lysis of predatory bacteria drives the enrichment of antibiotic resistance in soil microbial communities
Description
Several studies have investigated the effects of antibiotics on the evolution and maintenance of antimicrobial resistance (AMR). However, the impact of microbial interactions in antibiotic-free environments on resistance in natural communities remains unclear. Here, we investigated whether the predatory bacterium M. xanthus, which can produce antimicrobials as a prey-killing mechanisms, influences the abundance of antibiotic-resistant bacteria in its local environment, regardless of active predation. We observed an association between the presence of M. xanthus in soil and the frequency of antibiotic-resistant bacteria. Additionally, culture-based and metagenomic analysis showed that co-culturing M. xanthus with soil-derived communities in liquid cultures enriched AMR among non-myxobacterial isolates. This is because the lysis of M. xanthus, triggered during the starvation phase of the co-culture experiments, releases diffusible growth inhibitory compounds that enrich pre-existing resistant bacteria. Furthermore, our results show that death during multicellular fruiting body formation, a starvation-induced stress response in M. xanthus that results in over 90% cell death, also releases growth inhibitory molecules that enrich resistant bacteria. Hence, the higher abundance of resistant bacteria in the soil communities, where M. xanthus can be detected, was because of the diffusible growth-inhibitory substances that were released due to the death of M. xanthus cells during fruiting body formation. Together, our findings demonstrate how the death of M. xanthus, an important aspect of its life cycle, can impact antibiotic resistomes in natural soil communities without the anthropogenic influx of antibiotics.
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