Proteins that respond to the changes in copper availability include the assumed copper acquisition protein MopE, c-type heme proteins (SACCP, cytochrome c553o proteins) and several proteins of unknown function. The most intriguing observation is that multi-heme c-type cytochromes are major constituents of the M. capsulatus Bath surfaceome. This is not commonly observed in bacteria, but is a feature shared with the dissimilatory metal-reducing

bacteria. ZD1839 order Their presence on the M. capsulatus Bath cellular surface may be linked to the cells ability to efficiently adapt to changing growth conditions and environmental challenges. However, their possible role(s) in methane oxidation, nitrogen metabolism, copper acquisition, redox-reactions and/or electron transport remain(s) at present an open question. This review will discuss the possible significance of these findings. Methylococcus capsulatus (Bath) is one of the

most extensively studied methanotrophs. Its genome sequence was published in 2004 as GSK-3 assay the first complete genome sequence from an obligate methane oxidizing bacterium (Ward et al., 2004). One of the interesting findings uncovered by the genome sequencing was the extensive redundancy in several biological pathways, including gene duplications covering methane oxidation, carbon assimilation, amino acid biosynthesis, energy metabolism, transport, regulation and environmental sensing. Clostridium perfringens alpha toxin The high content of duplicated genes, and membrane modifying components, including

sterols, and trans fatty acids are consistent with an organism able to adapt to varying growth conditions (Bird et al., 1971; Jahnke et al., 1992; Loffler et al., 2010). Copper has a unique role in the biology of M. capsulatus Bath and its physiology changes dramatically with the bioavailability of this metal ion (recently reviewed by Semrau et al., 2010). At low copper-to-biomass regimes, methane is oxidized by the cytoplasmatic soluble methane monooxygenase (sMMO). When the growth conditions are changed to high copper-to-biomass ratios, sMMO is no longer produced and the methane oxidation is now mediated by a copper-containing particulate methane monooxygenase (pMMO), a regulation that takes place in the sub-μM range of copper (Stanley et al., 1983; Nielsen et al., 1996, 1997). The expression of pMMO is accompanied with the production of an extensive network of intracytoplasmic membranes where the oxidation of methane occurs (Prior & Dalton, 1985). This copper-dependent change in enzyme system for methane oxidation has been demonstrated for several methanotrophs possessing both MMO enzyme systems and is known as the copper switch (Murrell et al., 2000; Semrau et al., 2010).