ABSTRACT
In many bacterial species, the translational GTPase TypA acts as a global stress- and virulence regulator and also mediates resistance to the antimicrobial peptide BPI. On the chromosome of M. tuberculosis, typA is located next to narGHJI, which plays a role in adaptation of the pathogen to various environmental conditions. Here, we show that Mycobacterium tuberculosis is sensitive to P2, a derivative of BPI. Using a typA mutant of M. tuberculosis, we found this phenotype to be independent of TypA. We further tested typA expression in M. tuberculosis under defined stress conditions, such as oxygen- and nutrient depletion, low pH, heat shock, antibiotic stress and the presence of P2, and found that typA expression remains unaffected by any of these conditions. Analysis of growth and whole-genome expression revealed similar growth kinetics and gene expression profiles of the wild type and the mutant under normal growth conditions as well as under stress conditions. Our results suggest that in contrast to the findings in other bacteria, TypA does not act as a global stress- and virulence regulator in M. tuberculosis.
Subject(s)
Bacterial Proteins/physiology , GTP Phosphohydrolases/physiology , Gene Expression Regulation, Bacterial , Mycobacterium tuberculosis/physiology , Stress, Physiological , Adaptation, Physiological , Antimicrobial Cationic Peptides/pharmacology , Antimicrobial Cationic Peptides/physiology , Bacterial Proteins/genetics , Blood Proteins/pharmacology , Blood Proteins/physiology , GTP Phosphohydrolases/genetics , Gene Deletion , Gene Expression Profiling , Heat-Shock Response , Microbial Viability , Mycobacterium tuberculosis/genetics , Mycobacterium tuberculosis/growth & development , Mycobacterium tuberculosis/pathogenicity , Peptide Fragments/pharmacology , Peptide Fragments/physiology , Ribosomes/metabolism , Transcription, Genetic , VirulenceABSTRACT
Mycobacterium tuberculosis generally is assumed to depend on lipids as a major carbon and energy source when persisting within the host. The utilization of fatty acids requires a functional glyoxylate cycle with the key enzymes isocitrate lyase (Icl) and malate synthase. The open reading frame Rv0465c of M. tuberculosis H37Rv encodes a protein with significant sequence similarity to the transcriptional regulator RamB, which in Corynebacterium glutamicum controls the expression of several genes involved in acetate metabolism, i.e., those encoding enzymes of acetate activation and the glyoxylate cycle. We show here that the M. tuberculosis Rv0465c protein can functionally complement RamB in C. glutamicum and that it binds to the promoter regions of M. tuberculosis icl1 and Rv0465c. Construction and subsequent transcriptional and enzymatic analysis of a defined Rv0465c deletion mutant in M. tuberculosis revealed that the Rv0465c protein, now designated RamB, represses icl1 expression during growth with glucose and negatively autoregulates the expression of its own operon. Whole-genome microarray analysis of the M. tuberculosis ramB (ramB(MT)) mutant and the wild type furthermore showed that apart from icl1 and the ramB(MT) operon, the expression of all other M. tuberculosis genes involved in acetate metabolism remain unchanged in the mutant. Thus, RamB(MT) has a more specific regulatory function as RamB from C. glutamicum and is confined to expression control of icl1 and the ramB(MT) operon.
