Characterization and Transcriptome Analysis of Mycobacterium tuberculosis Persisters
ABSTRACTTuberculosis continues to be a major public health problem in many parts of the world. Significant obstacles in controlling the epidemic are the length of treatment and the large reservoir of latently infected people. Bacteria form dormant, drug-tolerant persister cells, which may be responsible for the difficulty in treating both acute and latent infections. We find that inMycobacterium tuberculosis, low numbers of drug-tolerant persisters are present in lag and early exponential phases, increasing sharply at late exponential and stationary phases to make up ~1% of the population. This suggests that persister formation is governed by both stochastic and deterministic mechanisms. In order to isolate persisters, an exponentially growing population was treated withd-cycloserine, and cells surviving lysis were collected by centrifugation. A transcriptome of persisters was obtained by using hybridization to an Affymetrix array. The transcriptome shows downregulation of metabolic and biosynthetic pathways, consistent with a certain degree of dormancy. A set of genes was upregulated in persisters, and these are likely involved in persister formation and maintenance. A comparison of the persister transcriptome with transcriptomes obtained for severalin vitrodormancy models identified a small number of genes upregulated in all cases, which may represent a core dormancy response.IMPORTANCEIt is estimated that every third person on the planet is infected withMycobacterium tuberculosis. The two major problems in controllingM. tuberculosisare the length of the treatment and the large reservoir of latently infected people. Dormant persister cells may be responsible for both problems. We find thatM. tuberculosisproduces persistersin vitroin a growth phase-dependent manner. Persisters were isolated from an exponentially growing population, and their transcriptome shows a distinct pattern of dormancy. These results give the first insight intoM. tuberculosispersisters and point to possible mechanisms responsible for their formation.