Browsing by Author "Hards, Kiel"

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Dual inhibition of the terminal oxidases eradicates antibiotic‐tolerant Mycobacterium tuberculosis
(EMBO, 2020-12) Lee, Bei Shi; Hards, Kiel; Engelhart, Curtis A.; Hasenoehrl, Erik J.; Kalia, Nitin P.; Mackenzie, Jared S.; Sviriaeva, Ekaterina; Chong, Shi Min Sherilyn; Manimekalai, Sony S.; Koh, Vanessa H.; Xu, Jiayong; Alonso, Sylvie; Miller, Marvin J.; Steyn, Adrie J.C.; Gruber, Gerhard; Schnappinger, Dirk; Berney, Michael; Cook, Gregory M.; Moraski, Garrett C.; Pethe, Kevin
The approval of bedaquiline has placed energy metabolism in the limelight as an attractive target space for tuberculosis antibiotic development. While bedaquiline inhibits the mycobacterial F1F0 ATP synthase, small molecules targeting other components of the oxidative phosphorylation pathway have been identified. Of particular interest is Telacebec (Q203), a phase 2 drug candidate inhibitor of the cytochrome bcc:aa3 terminal oxidase. A functional redundancy between the cytochrome bcc:aa3 and the cytochrome bd oxidase protects M. tuberculosis from Q203-induced death, highlighting the attractiveness of the bd-type terminal oxidase for drug development. Here, we employed a facile whole-cell screen approach to identify the cytochrome bd inhibitor ND-011992. Although ND-011992 is ineffective on its own, it inhibits respiration and ATP homeostasis in combination with Q203. The drug combination was bactericidal against replicating and antibiotictolerant, non-replicating mycobacteria, and increased efficacy relative to that of a single drug in a mouse model. These findings suggest that a cytochrome bd oxidase inhibitor will add value to a drug combination targeting oxidative phosphorylation for tuberculosis treatment.
Mixotrophy drives niche expansion of verrucomicrobial methanotrophs
(2017-08) Carere, Carlo R.; Hards, Kiel; Houghton, Karen M.; Power, Jean F.; McDonald, Ben; Collet, Christophe; Gapes, Daniel J.; Sparling, Richard; Boyd, Eric S.; Cook, Gregory M.; Greening, Chris; Stott, Matthew B.
Aerobic methanotrophic bacteria have evolved a specialist lifestyle dependent on consumption of methane and other short-chain carbon compounds. However, their apparent substrate specialism runs contrary to the high relative abundance of these microorganisms in dynamic environments, where the availability of methane and oxygen fluctuates. In this work, we provide in situ and ex situ evidence that verrucomicrobial methanotrophs are mixotrophs. Verrucomicrobia-dominated soil communities from an acidic geothermal field in Rotokawa, New Zealand rapidly oxidised methane and hydrogen simultaneously. We isolated and characterised a verrucomicrobial strain from these soils, Methylacidiphilum sp. RTK17.1, and showed that it constitutively oxidises molecular hydrogen. Genomic analysis confirmed that this strain encoded two [NiFe]-hydrogenases (group 1d and 3b), and biochemical assays revealed that it used hydrogen as an electron donor for aerobic respiration and carbon fixation. While the strain could grow heterotrophically on methane or autotrophically on hydrogen, it grew optimally by combining these metabolic strategies. Hydrogen oxidation was particularly important for adaptation to methane and oxygen limitation. Complementary to recent findings of hydrogenotrophic growth by Methylacidiphilum fumariolicum SolV, our findings illustrate that verrucomicrobial methanotrophs have evolved to simultaneously utilise hydrogen and methane from geothermal sources to meet energy and carbon demands where nutrient flux is dynamic. This mixotrophic lifestyle is likely to have facilitated expansion of the niche space occupied by these microorganisms, allowing them to become dominant in geothermally influenced surface soils. Genes encoding putative oxygen-tolerant uptake [NiFe]-hydrogenases were identified in all publicly available methanotroph genomes, suggesting hydrogen oxidation is a general metabolic strategy in this guild.