Chloramphenicol-mobilized Bacillus subtilis elevates transient expression of multiple antibiotic resistance genes, including the glycopeptides phleomycin and bleomycin

Antibiotic resistance is a global crisis that stems from the use of antibiotics as an essential part of modern medicine. Understanding how antibiotic resistance is controlled among cells in bacterial populations will provide insights into how antibiotics shape microbial communities. Here, we describe patterns of B. subtilis gene expression that arise from growth on a surface either in isolation or under subinhibitory chloramphenicol exposure. We identified elevated expression of genes encoding five different antibiotic resistance functions. The expression of four of the five resistance functions is controlled by a combination of terminator attenuation and transcriptional regulation. Two of these, vmlR and tlrB provide resistance to lincosamides and tylosin, respectively. We found that bmrCD promotes resistance to glycopeptides, including phleomycin and bleomycin. Promoter fusions to luciferase were used to follow expression of bmrCD, vmlR, and tlrB. Subinhibitory chloramphenicol exposure induces sliding motility of B. subtilis, wherein the three antibiotic resistance functions are expressed heterogeneously in spatiotemporally segregated pattern. We found that their expression is transiently elevated even in the absence of antibiotic exposure. The data suggest that for some antibiotics, intrinsic resistance genes are entrained to changes in growth and metabolism. Antibiotic exposure amplifies their expression, potentially providing a subpopulation of cells elevated protection to multiple classes of antibiotic. IMPORTANCEAntibiotics are a natural component of bacterial communities that are vital to modern medicine and to combatting antibiotic-resistant pathogens. Understanding the roles antibiotics play in microbial populations provides insights to the origins of antibiotic resistance. Many studies show that subinhibitory concentrations of antibiotics stimulate bacterial gene expression, including antibiotic resistance, and influence community dynamics. This study shows that bacteria on an agar surface transiently elevate expression of intrinsic resistance genes for multiple antibiotics. Subinhibitory chloramphenicol exposure stimulates the bacterial population both to expand across the surface and enhance expression of the resistance genes in a heterogeneous pattern. The results illustrate how exposure to some antibiotics substantially changes bacterial population dynamics that include the spatiotemporally controlled expression of endogenous antibiotic resistance.