Department of Microbiology and Cell Science, University of Floridagrid.15276.37, Merritt Island, Florida, USA.
Appl Environ Microbiol. 2022 Mar 8;88(5):e0242221. doi: 10.1128/aem.02422-21. Epub 2022 Jan 19.
RNA polymerase (RNAP) is a highly conserved macromolecular machine that contributes to the flow of genetic information from genotype to phenotype. In Bacillus subtilis, mutations in the gene encoding the β-subunit of RNAP have been shown to alter a number of global phenotypes, including growth, utilization of unusual nutrient sources, sporulation, germination, and production of secondary metabolites. In addition, the spectrum of mutations in leading to rifampin resistance (Rif) can change dramatically depending upon the environment to which B. subtilis cells or spores are exposed. Rif mutations have historically been associated with slower growth and reduced fitness; however, these assessments of fitness were conducted on limited collections of mutants in rich laboratory media that poorly reflect natural environments typically inhabited by B. subtilis. Using a novel deep-sequencing approach in addition to traditional measurements of growth rate, lag time, and pairwise competitions, we demonstrated that the competitive advantages of specific alleles differ depending on the growth environment in which they are determined. Microbial resistance to antibiotics is a growing threat to public health across the world. Historically, resistance to antibiotics has been associated with reduced fitness. A growing body of evidence indicates that resistance to rifampin, a frontline antibiotic used to treat mycobacterial and biofilm-associated infections, may increase fitness given an appropriate environment even in the absence of the selective antibiotic. Here, we experimentally confirm this phenomenon by directly comparing the fitness of multiple rifampin-resistant mutants of Bacillus subtilis in rich LB medium and an asparagine minimal medium. Our research demonstrates that the fitness cost of rifampin resistance can vary greatly depending upon the environment. This has important implications for understanding how microbes develop antimicrobial resistance in the absence of antibiotic selection.
RNA 聚合酶（RNAP）是一种高度保守的大分子机器，有助于遗传信息从基因型到表型的流动。在枯草芽孢杆菌中，RNAP 的β亚基编码基因的突变已被证明会改变许多全局表型，包括生长、利用不寻常的营养源、孢子形成、萌发和次生代谢产物的产生。此外，导致利福平耐药（Rif）的 基因突变谱可以根据枯草芽孢杆菌细胞或孢子暴露的环境而发生巨大变化。 Rif 突变历来与生长缓慢和适应性降低有关；然而，这些适应性评估是在丰富的实验室培养基中对有限的突变体集合进行的，这些培养基很难反映枯草芽孢杆菌通常居住的自然环境。除了传统的生长率、迟滞时间和成对竞争测量外，我们还使用了一种新的深度测序方法，证明了特定 等位基因的竞争优势取决于它们所处的生长环境。
抗生素耐药性是全世界公共卫生面临的一个日益严重的威胁。历史上，抗生素耐药性与适应性降低有关。越来越多的证据表明，即使没有选择性抗生素，利福平（一种用于治疗分枝杆菌和生物膜相关感染的一线抗生素）的耐药性也可能在适当的环境中增加适应性。在这里，我们通过直接比较枯草芽孢杆菌的多个利福平耐药突变体在丰富的 LB 培养基和天冬酰胺最小培养基中的适应性，实验证实了这一现象。我们的研究表明，利福平耐药性的适应性成本可能会因环境而异。这对于理解微生物在没有抗生素选择的情况下如何产生抗微生物耐药性具有重要意义。
