Tetracycline tolerance mediated by gene amplification in Bacillus subtilis

Abstract

Bacillus subtilis can acquire a higher tolerance to tetracycline by increasing the gene dosage of its resistance gene tetB. In this study, we estimated the multiplication effect of tetB on tetracycline tolerance. Cells harbouring multiple copies of tetB were found to comprise approximately 30 % of the total tetracycline-resistant cell population when selected on medium containing 10 mg tetracycline ml "1. Disruption of recA resulted in a significant decrease in the frequency of tetB amplification. Although four direct repeats exist around tetB, the majority of tetB amplicons were found to be flanked by non-homologous sequences, indicating that the initial duplication of tetB can occur largely through RecA-independent recombination. The correlation between the tetB copy number and the MIC values for tetracycline indicated that more than three copies of tetB were required for tolerance to 10 mg tetracycline ml "1 . Thus, the RecA-dependent expansion step appears to be necessary for developing significant tetracycline tolerance mediated by tetB amplification.

Mechanisms of protein evolution

“…107 Under strong selection, multiple copies of a gene mediating survival may emerge within a strikingly small number of generations and disappear immediately after selection is removed. 108,109 Given high replication fidelity, the above-discussed mechanisms may be crucial in shortening the time gap between new challenges and the arrival of mutations that promote survival. 110 It is not trivial to establish direct causality between stress, the induction of genetic changes, and adaptation.…”

“…Duplications can vary from gene segments to whole genomes and may also be considered as “adaptive mutations,” whenever they are stress‐induced and auto‐amplified 107 . Under strong selection, multiple copies of a gene mediating survival may emerge within a strikingly small number of generations and disappear immediately after selection is removed 108,109 …”

Growth and sporulation defects in Bacillus subtilis mutants with a single rrn operon can be suppressed by amplification of the rrn operon

“…In the present study, both pathways, SHDIR and SHIIR, may be involved in B. subtilis rrn amplification. It was recently reported that recA-independent duplication of the tetB gene, which confers tetracycline resistance in B. subtilis (Wannarat et al 2014), may not require RecA activity for the initial duplication event.…”

Dissecting transmembrane bicarbonate transport by 1,8-di(thio)amidocarbazoles

“…The growth of B. subtilis is significantly inhibited by all tested transporters, with MICs of 2-4 even lower than that of antibiotic tetracycline (MIC = 11.3 µM). 29 Noteworthy, the MIC values for 1-4 correlate with their H + Cl − transport activity in liposomal assays. Remarkably, thioamide 2 exhibits particularly strong antibacterial properties against S. aureus, the second leading pathogen responsible for antimicrobial resistance-associated deaths in 2019.…”

“…In fact, the antibacterial properties of synthetic anionophores often correlate with their anion transport activity. 8,9,23,24,25,26,29 However, some deviations from this rule 27 indicate, that the rate of anion transport is not the only factor responsible for antimicrobial activity of synthetic ionophores. Further biological studies with transporters that act via different mechanisms may be helpful in order to learn more about the origins of the antibacterial properties of ionophores.…”