Dataset Information

Two isozymes of particulate methane monooxygenase with different methane oxidation kinetics are found in Methylocystis sp. strain SC2.

ABSTRACT: Methane-oxidizing bacteria (methanotrophs) attenuate methane emission from major sources, such as wetlands, rice paddies, and landfills, and constitute the only biological sink for atmospheric methane in upland soils. Their key enzyme is particulate methane monooxygenase (pMMO), which converts methane to methanol. It has long been believed that methane at the trace atmospheric mixing ratio of 1.75 parts per million by volume (ppmv) is not oxidized by the methanotrophs cultured to date, but rather only by some uncultured methanotrophs, and that type I and type II methanotrophs contain a single type of pMMO. Here, we show that the type II methanotroph Methylocystis sp. strain SC2 possesses two pMMO isozymes with different methane oxidation kinetics. The pmoCAB1 genes encoding the known type of pMMO (pMMO1) are expressed and pMMO1 oxidizes methane only at mixing ratios >600 ppmv. The pmoCAB2 genes encoding pMMO2, in contrast, are constitutively expressed, and pMMO2 oxidizes methane at lower mixing ratios, even at the trace level of atmospheric methane. Wild-type strain SC2 and mutants expressing pmoCAB2 but defective in pmoCAB1 consumed atmospheric methane for >3 months. Growth occurred at 10-100 ppmv methane. Most type II but no type I methanotrophs possess the pmoCAB2 genes. The apparent K(m) of pMMO2 (0.11 muM) in strain SC2 corresponds well with the K(m(app)) values for methane oxidation measured in soils that consume atmospheric methane, thereby explaining why these soils are dominated by type II methanotrophs, and some by Methylocystis spp., in particular. These findings change our concept of methanotroph ecology.

SUBMITTER: Baani M

PROVIDER: S-EPMC2481331 | biostudies-literature | 2008 Jul

REPOSITORIES: biostudies-literature

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Two isozymes of particulate methane monooxygenase with different methane oxidation kinetics are found in Methylocystis sp. strain SC2.

Baani Mohamed M Liesack Werner W

Proceedings of the National Academy of Sciences of the United States of America 20080715 29

Methane-oxidizing bacteria (methanotrophs) attenuate methane emission from major sources, such as wetlands, rice paddies, and landfills, and constitute the only biological sink for atmospheric methane in upland soils. Their key enzyme is particulate methane monooxygenase (pMMO), which converts methane to methanol. It has long been believed that methane at the trace atmospheric mixing ratio of 1.75 parts per million by volume (ppmv) is not oxidized by the methanotrophs cultured to date, but rathe ...[more]

PMID: 18632585

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Project description:Soil microorganisms have to rapidly respond to salt-induced osmotic stress. Type II methanotrophs of the genus Methylocystis are widely distributed in upland soils but are known to have a low salt tolerance. Here, we tested the ability of Methylocystis sp. strain SC2 to adapt to increased salinity. When exposed to 0.75% NaCl, methane oxidation was completely inhibited for 2.25 h and fully recovered within 6 h. Growth was inhibited for 23.5 h and then fully recovered. Its transcriptome was profiled after 0 min (control), 45 min (early response), and 14 h (late response) of stress exposure. Physiological and transcriptomic stress responses corresponded well. Salt stress induced the differential expression of 301 genes, with sigma factor ?32 being a major controller of the transcriptional stress response. The transcript levels of nearly all the genes involved in oxidizing CH4 to CO2 remained unaffected, while gene expression involved in energy-yielding reactions (nuoA-N) recovered concomitantly with methane oxidation from salt stress shock. Glutamate acted as an osmoprotectant. Its accumulation in late stress response corresponded to increased production of glutamate dehydrogenase 1. Chromosomal genes whose products (stress-induced protein, DNA-binding protein from starved cells, and CsbD family protein) are known to confer stress tolerance showed increased expression. On plasmid pBSC2-1, genes encoding type IV secretion system and single-strand DNA-binding protein were upregulated in late response, suggesting stress-induced activation of the plasmid-borne conjugation machinery. Collectively, our results show that Methylocystis sp. strain SC2 is able to adapt to salt stress, but only within a narrow range of salinities.IMPORTANCE Besides the oxic interface of methanogenic environments, Methylocystis spp. are widely distributed in upland soils, where they may contribute to the oxidation of atmospheric methane. However, little is known about their ability to cope with changes in soil salinity. Growth and methane oxidation of Methylocystis sp. strain SC2 were not affected by the presence of 0.5% NaCl, while 1% NaCl completely inhibited its activity. This places strain SC2 into the low-salt-tolerance range reported for other Methylocystis species. Our results show that, albeit in a narrow range, strain SC2 is able to respond and adapt to salinity changes. It possesses various stress response mechanisms, which allow resumption of growth within 24 h when exposed to 0.75% NaCl. Presumably, these mechanisms allow Methylocystis spp., such as strain SC2, to thrive in upland soils and to adapt to certain fluctuations in soil salinity.

Dataset Information

Two isozymes of particulate methane monooxygenase with different methane oxidation kinetics are found in Methylocystis sp. strain SC2.

Publications

Two isozymes of particulate methane monooxygenase with different methane oxidation kinetics are found in Methylocystis sp. strain SC2.

Similar Datasets

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