An active beta-lactamase is a part of an orchestrated cell wall stress resistance network of Bacillus subtilis and related rhizosphere species

A hallmark of the Gram-positive bacteria, such as the soil-dwelling bacterium Bacillus subtilis, is their cell wall. Here, we report that d-leucine and flavomycin, biofilm inhibitors targeting the cell wall, activate the beta-lactamase PenP. This beta-lactamase contributes to ampicillin resistance in B. subtilis under all conditions tested. In contrast, both Spo0A, a master regulator of nutritional stress, and the general cell wall stress response, differentially contribute to beta-lactam resistance under different conditions. To test whether beta-lactam resistance and beta-lactamase genes are widespread in other Bacilli, we isolated Bacillus species from undisturbed soils, and found that their genomes can encode up to five beta-lactamases with differentiated activity spectra. Surprisingly, the activity of environmental beta-lactamases and PenP, as well as the general stress response, resulted in a similarly reduced lag phase of the culture in the presence of beta-lactam antibiotics, with little or no impact on the logarithmic growth rate. The length of the lag phase may determine the outcome of the competition between beta-lactams and beta-lactamases producers. Overall, our work suggests that antibiotic resistance genes in B. subtilis and related species are ancient and widespread, and could be selected by interspecies competition in undisturbed soils.