Impact of Copper on the Physiology and Transcriptome of Methylosinus Trichosporium OB3b Grown on Either Methane or Methanol

TL;DR

Copper inhibits the growth of Methylosinus trichosporium OB3b on methanol by causing metabolic imbalances and stress.

Contribution

The study reveals how copper disrupts methanol metabolism and gene expression in a model methane-consuming bacterium.

Findings

Copper prevents growth on methanol by causing overgeneration of reducing power and formate accumulation.

Copper and methanol together repress siderophore gene clusters, which may be important for metal homeostasis.

Growth on methanol is possible in copper's presence if pH is stabilized with MOPS buffer.

Abstract

Methylosinus trichosporium
OB3b is a model methanotroph that converts methane to CO2 with methanol, formaldehyde, and formate as intermediates. Here we show that copper has a significant impact on the ability of Msn. trichosporium OB3b to grow on methanol, that is, growth consistently occurred on methanol in the absence of copper but not in its presence. Growth on methanol in the presence of copper, however, occurred in the presence of MOPS buffer that stabilized pH. Examination of transcriptome profiles, NADH/NAD ratios, and formate production indicates that growth disruption in the presence of copper was likely caused by a confluence of (1) overgeneration of reducing power from methanol oxidation; (2) formate accumulation leading to acidification of the growth medium and inactivation of formate dehydrogenase; and (3) lack of expression of oxidative stress defence genes. Finally, transcriptomic analysis showed that expression of two putative siderophore gene clusters (one on a plasmid and the other on the chromosome) was significantly controlled by both the availability of copper as well as growth substrate (i.e., methane vs. methanol). Specifically, the presence of methanol and copper significantly repressed the expression of these siderophore gene clusters, suggesting that these metallophores play a key role in facilitating methanotrophic growth.

Methylosinus trichosporium
OB3b can grow on methanol in the absence but not presence of copper due: (1) overgeneration of reducing power from methanol oxidation; (2) formate accumulation leading to acidification of the growth medium and inactivation of formate dehydrogenase; and (3) lack of expression of potential oxidative stress defence genes.

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