Culviner, P. | bioRxiv Science

bioRxiv2022

Tuberculosis treatment failure associated with evolution of antibiotic resilience

Antibiotics are a cornerstone of medicine, placing bacterial pathogens under intense pressure to evolve new survival mechanisms. Analysis of 51,229 Mycobacterium tuberculosis (Mtb) clinical isolates identified an essential transcriptional regulator, Rv1830 (here named resR) as a frequent target of positive (adaptive) selection. resR mutants do not demonstrate canonical drug resistance or drug tolerance but instead have significantly faster recovery after drug treatment across all antibiotics and combinations tested, a phenotype which we term antibiotic resilience. ResR acts in a regulatory cascade with other growth-controlling transcriptional regulators WhiB2 and WhiA, which are also under positive selection in Mtb clinical isolates. Mutations of these genes are associated with treatment failure and the acquisition of canonical drug resistance.

microbiology↗

bioRxiv2020

Stress induces the transcription of toxin-antitoxin systems but does not activate toxin

Toxin-antitoxin (TA) systems are ubiquitous genetic elements in bacterial genomes, but their functions are controversial. Although they are frequently postulated to regulate cell growth following stress, few null phenotypes for TA systems have been reported. Here, we show that TA transcript levels can increase substantially in response to stress, but toxin is not liberated. We find that the growth of an Escherichia coli strain lacking 10 TA systems encoding endoribonuclease toxins is not affected following exposure to six stresses that each trigger TA transcription. Additionally, using RNA-sequencing, we find no evidence of mRNA cleavage following stress. Stress-induced transcription arises from antitoxin degradation and relief of transcriptional autoregulation. Importantly, although free antitoxin is readily degraded in vivo, antitoxin bound to toxin is protected from proteolysis, preventing release of active toxin. Thus, transcription is not a reliable marker of TA activity, and TA systems likely do not strongly promote survival following stress.

microbiology↗