Journal Article

Unique Flexibility in Energy Metabolism Allows Mycobacteria to Combat Starvation and Hypoxia

Cook, Gregory M., Berney, Michael

2010

Overview

Mycobacteria are a group of obligate aerobes that require oxygen for growth, but paradoxically have the ability to survive and metabolize under hypoxia. The mechanisms responsible for this metabolic plasticity are unknown. Here, we report on the adaptation of Mycobacterium smegmatis to slow growth rate and hypoxia using carbon-limited continuous culture. When M. smegmatis is switched from a 4.6 h to a 69 h doubling time at a constant oxygen saturation of 50%, the cells respond through the down regulation of respiratory chain components and the F1Fo-ATP synthase, consistent with the cells lower demand for energy at a reduced growth rate. This was paralleled by an up regulation of molecular machinery that allowed more efficient energy generation (i.e. Complex I) and the use of alternative electron donors (e.g. hydrogenases and primary dehydrogenases) to maintain the flow of reducing equivalents to the electron transport chain during conditions of severe energy limitation. A hydrogenase mutant showed a 40% reduction in growth yield highlighting the importance of this enzyme in adaptation to low energy supply. Slow growing cells at 50% oxygen saturation subjected to hypoxia (0.6% oxygen saturation) responded by switching on oxygen scavenging cytochrome bd, proton-translocating cytochrome bc1-aa3 supercomplex, another putative hydrogenase, and by substituting NAD+-dependent enzymes with ferredoxin-dependent enzymes thus highlighting a new pattern of mycobacterial adaptation to hypoxia. The expression of ferredoxins and a hydrogenase provides a potential conduit for disposing of and transferring electrons in the absence of exogenous electron acceptors. The use of ferredoxin-dependent enzymes would allow the cell to maintain a high carbon flux through its central carbon metabolism independent of the NAD+/NADH ratio. These data demonstrate the remarkable metabolic plasticity of the mycobacterial cell and provide a new framework for understanding their ability to survive under low energy conditions and hypoxia.

• Publisher: Public Library of Science,Public Library of Science (PLoS)
• Subject: Adaptation / Aerobes / Alternative energy / ATP synthase / Carbon / Cell culture / Citric Acid Cycle / Cloning / Continuous culture / Cytochrome / Cytochrome bc1 / Cytochrome bd / Electron Transport / Electron transport chain / Electrons / Energy limitation / Energy Metabolism / Enzymes / Ferredoxin / Flexibility / Gene expression / Gene Expression Regulation, Bacterial / Genes, Bacterial / Glycerol / Glyoxylates - metabolism / Growth rate / Helicobacter pylori / Hydrogenase / Hypoxia / Immunology / Iron proteins / Laboratories / Machinery and equipment / Medical research / Metabolism / Metabolites / Microbiology/Applied Microbiology / Microbiology/Cellular Microbiology and Pathogenesis / Microbiology/Environmental Microbiology / Microbiology/Medical Microbiology / Microbiology/Microbial Growth and Development / Microbiology/Microbial Physiology and Metabolism / Microscopy / Molecular machines / Multigene Family / Mutagenesis / Mycobacterium smegmatis / Mycobacterium smegmatis - genetics / Mycobacterium smegmatis - growth & development / Mycobacterium smegmatis - metabolism / Mycobacterium smegmatis - physiology / Mycobacterium tuberculosis / NAD / NADH / Nicotinamide adenine dinucleotide / Oxidoreductases / Oxygen / Oxygen - metabolism / Oxygen content / Pathogens / Physiological aspects / Plastic properties / Plasticity / Polymerase chain reaction / Salmonella / Salmonella Typhimurium / Saturation / Signal Transduction / Starvation / Studies / Switching / Tuberculosis