Metabolite Profiling of Mycobacterium species: Biochemical Diversity and Adaptation to Nutrient Limitation and Drug Treatments

The Mycobacterium genus is known for its most prominent species Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis. Over the last few decades, the increasing occurrence of drug-resistant Mtb strains has resulted in renewed interest in Mtb and related Mycobacterium species. In recent years, the lack of knowledge of metabolic networks underlying phenotypes in Mycobacterium species has led to a need for metabolite profiling platforms in these organisms.
In the present study, M. smegmatis, a fast-growing Mycobacterium species, and M. bovis Bacillus Calmette-Guérin (M. bovis BCG), the tuberculosis vaccine, were utilised as model organisms to develop a metabolite profiling platform for Mycobacterium species including quenching and extraction procedures for GC/MS and UPLC analysis.
The optimised protocol was applied to monitor metabolic changes of the two model organisms as well as M. phlei, M. avium and M. intracellulare, during three different culture conditions including limitations of nutrients and different oxygen concentrations. The metabolite profiling platform was also exploited in order to reveal metabolic changes of M. smegmatis, M. phlei and M. avium under treatment with the drugs ethambutol, isoniazid and fosmidomycin, under aerobic and hypoxic cultivation.
The limitations of nutrients and oxygen as well as the effects of the drug treatments highlighted several metabolic changes, corresponding to specific or general cellular responses to the culture condition. A general response to stress-inducing conditions of all Mycobacterium species tested was metabolic changes related to cell wall synthesis and maintenance, including the activation of the glyoxylate shunt. Under hypoxia, metabolic reactions specific to the growth rate used were revealed such as TAG secretion for fast-growing species and poly-L-glutamate production for slow-growing species.
Furthermore, the metabolic information from this study was combined with previously published “omics” research on Mycobacterium species. This revealed that the responses to different culture conditions seem to be controlled by transcriptional rather than post-transcriptional regulation. This type of regulation was emphasised under drug treatments as cellular responses were detected as an adaptation towards resistance against the drugs used.
Overall, the metabolite data highlighted the importance of several metabolic processes which could be exploited as new drug targets.