title: The growth and survival of Mycobacterium smegmatis is enhanced by co-metabolism of atmospheric H2.
abstract: The soil bacterium Mycobacterium smegmatis is able to scavenge the trace concentrations of H2 present in the atmosphere, but the physiological function and importance of this activity is not understood. We have shown that atmospheric H2 oxidation in this organism depends on two phylogenetically and kinetically distinct high-affinity hydrogenases, Hyd1 (MSMEG_2262-2263) and Hyd2 (MSMEG_2720-2719). In this study, we explored the effect of deleting Hyd2 on cellular physiology by comparing the viability, energetics, transcriptomes, and metabolomes of wild-type vs. Δhyd2 cells. The long-term survival of the Δhyd2 mutant was significantly reduced compared to the wild-type. The mutant additionally grew less efficiently in a range of conditions, most notably during metabolism of short-chain fatty acids; there was a twofold reduction in growth rate and growth yield of the Δhyd2 strain when acetate served as the sole carbon source. Hyd1 compensated for loss of Hyd2 when cells were grown in a high H2 atmosphere. Analysis of cellular parameters showed that Hyd2 was not necessary to generate the membrane potential, maintain intracellular pH homeostasis, or sustain redox balance. However, microarray analysis indicated that Δhyd2 cells were starved for reductant and compensated by rewiring central metabolism; transcripts encoding proteins responsible for oxidative decarboxylation pathways, the urea cycle, and ABC transporter-mediated import were significantly more abundant in the Δhyd2 mutant. Metabolome profiling consistently revealed an increase in intracellular amino acids in the Δhyd2 mutant. We propose that atmospheric H2 oxidation has two major roles in mycobacterial cells: to generate reductant during mixotrophic growth and to sustain the respiratory chain during dormancy.
authors: University of Otago, Department of Microbiology and Immunology, Dunedin, New Zealand.
authors: Chris
authors: C
authors: Greening
authors: University of Auckland, The Centre for Microbial Innovation, Auckland, New Zealand.
authors: Silas G
authors: SG
authors: Villas-Bôas
authors: University of Otago, Department of Microbiology and Immunology, Dunedin, New Zealand.
authors: Jennifer R
authors: JR
authors: Robson
authors: University of Otago, Department of Microbiology and Immunology, Dunedin, New Zealand; Albert Einstein College of Medicine, Department of Microbiology and Immunology, Bronx, New York, United States of America.
authors: Michael
authors: M
authors: Berney
authors: University of Otago, Department of Microbiology and Immunology, Dunedin, New Zealand.
authors: Gregory M
authors: GM
authors: Cook
mesh_terms: D019342:Acetic Acid / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism; D001272:Atmosphere / Q000737:chemistry; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D004734:Energy Metabolism / Q000235:genetics; D005232:Fatty Acids, Volatile / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D006859:Hydrogen / Q000378:metabolism*; D055442:Metabolome; D050296:Microbial Viability; D020102:Mycobacterium smegmatis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000172:deficiency / Q000235:genetics* / Q000378:metabolism; D012988:Soil Microbiology; D059467:Transcriptome
chemical_list: D000596:Amino Acids; D001426:Bacterial Proteins; D005232:Fatty Acids, Volatile; D006859:Hydrogen; D010088:Oxidoreductases; C029746:uptake hydrogenase; D019342:Acetic Acid