Abstract
BackgroundThe aerobic fast-growing Mycobacterium smegmatis, like its slow-growing pathogenic counterpart Mycobacterium tuberculosis, has the ability to adapt to microaerobiosis by shifting from growth to a non-proliferating or dormant state. The molecular mechanism of dormancy is not fully understood and various hypotheses have been formulated to explain it. In this work, we open new insight in the knowledge of M. smegmatis dormancy, by identifying and characterizing genes involved in this behavior.ResultsIn a library generated by transposon mutagenesis, we searched for M. smegmatis mutants unable to survive a coincident condition of hypoxia and low carbon content, two stress factors supposedly encountered in the host and inducing dormancy in tubercle bacilli. Two mutants were identified that mapped in the uvrA gene, coding for an essential component of the Nucleotide Excision Repair system (NER). The two mutants showed identical phenotypes, although the respective transposon insertions hit different regions of the uvrA gene. The restoration of the uvrA activity in M. smegmatis by complementation with the uvrA gene of M. tuberculosis, confirmed that i) uvrA inactivation was indeed responsible for the inability of M. smegmatis cells to enter or exit dormancy and, therefore, survive hypoxia and presence of low carbon and ii) showed that the respective uvrA genes of M. tuberculosis and M. smegmatis are true orthologs. The rate of survival of wild type, uvrA mutant and complemented strains under conditions of oxidative stress and UV irradiation was determined qualitatively and quantitatively.ConclusionsTaken together our results confirm that the mycobacterial NER system is involved in adaptation to various stress conditions and suggest that cells with a compromised DNA repair system have an impaired dormancy behavior.
Highlights
The aerobic fast-growing Mycobacterium smegmatis, like its slow-growing pathogenic counterpart Mycobacterium tuberculosis, has the ability to adapt to microaerobiosis by shifting from growth to a nonproliferating or dormant state
M. smegmatis dormancy is induced under conditions of low oxygen and low carbon availability In order to develop a simple and reliable strategy to screen a M. smegmatis library for mutants unable to grow in conditions of hypoxia and low carbon concentration, we first compared the effects of these conditions on the dormancy behavior of M. smegmatis wt and ppk1- mutant cells [the latter were used as a control as they have been recently reported to be sensitive to hypoxic condition [20]]
Similar results were obtained for the ppk mutant. These results indicate that the M. smegmatis growth rate is significantly limited by the amount of carbon source
Summary
The aerobic fast-growing Mycobacterium smegmatis, like its slow-growing pathogenic counterpart Mycobacterium tuberculosis, has the ability to adapt to microaerobiosis by shifting from growth to a nonproliferating or dormant state. Mycobacterium tuberculosis, the etiological agent of tuberculosis, has the ability to enter human macrophages and survive inside them in a ‘latent’ or ‘non-proliferating’ form for a long period of time. This behavior is termed dormancy or latency. The molecular mechanism allowing dormancy is not fully understood due the lack of experimental systems that can closely mimic human latent infections [1]. Conditions of nutrient limitation have been used to investigate the ability of M. tuberculosis to persist in a non-growing state for long periods of time [7,8,9]. Dormancy is a common behavior to both pathogenic and non-pathogenic mycobacteria, in vitro [4,10,11], allowing the study of pathogenic species by using non-pathogens as model
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
