Growth of a non-methanotroph on natural gas: ignoring the obvious to focus on the obscure

Identity and mechanisms of alkane-oxidizing metalloenzymes from deep-sea hydrothermal vents

Six aerobic alkanotrophs (organism that can metabolize alkanes as their sole carbon source) isolated from deep-sea hydrothermal vents were characterized using the radical clock substrate norcarane to determine the metalloenzyme and reaction mechanism used to oxidize alkanes. The organisms studied were Alcanivorax sp. strains EPR7 and MAR14, Marinobacter sp. strain EPR21, Nocardioides sp. strains EPR26w, EPR28w, and Parvibaculum hydrocarbonoclasticum strain EPR92. Each organism was able to grow on n-alkanes as the sole carbon source and therefore must express genes encoding an alkane-oxidizing enzyme. Results from the oxidation of the radical-clock diagnostic substrate norcarane demonstrated that five of the six organisms (EPR7, MAR14, EPR21, EPR26w, and EPR28w) used an alkane hydroxylase functionally similar to AlkB to catalyze the oxidation of medium-chain alkanes, while the sixth organism (EPR92) used an alkane-oxidizing cytochrome P450 (CYP)-like protein to catalyze the oxidation. DNA sequencing indicated that EPR7 and EPR21 possess genes encoding AlkB proteins, while sequencing results from EPR92 confirmed the presence of a gene encoding CYP-like alkane hydroxylase, consistent with the results from the norcarane experiments.

The microbial methane cycle

This special issue highlights several recent discoveries in the microbial methane cycle, including the diversity and activity of methanotrophic bacteria in special habitats, distribution and contribution of the newly discovered Verrucomicrobia, metabolism of methane and related one-carbon compounds such as methanol and methylamine in freshwater and marine environments, methanol and methane-dependent nitrate reduction, the relationships of methane cycle microorganisms with plants and animals, and the environmental factors that regulate microbial processes of the methane cycle. These articles also highlight the plethora of new organisms and metabolism relating to the methane cycle that have been discovered in recent years and outline the many questions in the methane cycle that still need to be addressed. It is clear that despite a tremendous amount of research on the biology of the methane cycle, the microbes involved in catalysing methane production and consumption harbour many secrets that need to be disclosed in order for us to fully understand how the biogeochemical methane cycle is regulated in the environment, and for us to make future predictions about the global sources and sinks of methane and how anthropogenic changes impact on the cycling of this important greenhouse gas.