A metabolomics approach investigating the functionality of the ESX-1 gene cluster in mycobacteria
Swanepoel, Conrad Cilliers
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Tuberculosis (TB) claims the lives of millions of individuals each year, and is consequently the world’s second-most deadly infectious disease after acquired immune deficiency syndrome (AIDS), responsible for 1.4 million deaths in 2010 alone. Developing countries carry the heaviest burden, with the occurrence of multidrug-resistant (MDR) TB becoming more frequent, making more efficient vaccination and treatment strategies a necessity to combat this epidemic. The ESX-1 gene cluster (encoding the virulence-associated proteins ESAT-6 and CFP-10) and the Type Vll secretion system are thought to be responsible for the transport of extracellular proteins across the hydrophobic, and highly impermeable, cell wall of Mycobacterium, and consequently are thought to play a role in the virulence of this organism. To date, our understanding of tuberculosis pathophysiology and virulence has been described primarily using proteomic and genomic approaches. Subsequently, using the relatively new research approach called metabolomics, and interpreting the data using systems biology, we aimed to identify new metabolite markers that better characterise virulence and the proteins involved, more specifically related to the ESX-1 gene cluster. Using a GCxGC-TOFMS metabolomics research approach, we compared the varying metabolomes of M. smegmatis ESX-1 knock-out (ESX-1ms) to that of the wild-type parent strain and subsequently identified those metabolite markers differing between these strains. Multivariate and univariate statistical analyses of the analysed metabolome were used to identify those metabolites contributing most to the differences seen between the two sample groups. A general increase in various carbohydrates, amino acids and lipids, associated with cell wall structure and function, were detected in the ESX-1ms strain relative to the wild-type parent strain. Additionally, metabolites associated with the antioxidant system, virulence protein formation and energy production in these mycobacteria, were also seen to differ between the two groups. This metabolomics investigation is the first to identify the metabolite markers confirming the role of the ESX-1 gene cluster with virulence and the underlying metabolic pathways, as well as its associated role with increased metabolic activity, growth/replication rates, increased cell wall synthesis and an altered antioxidant mechanism, all of which are believed to contribute to this organism’s increased pathogenicity and survival ability.