Energy conservation in whole cells of the methylotrophic bacterium Methylophilus methylotrophus

Energy conservation in aerobically grown Staphylococcus aureus

The present studies provide new data on the involvement of menaquinol oxidases in substrate oxidation and energy conservation in aerobically grown, resting cells of Staphylococcus aureus 17810R, starved of endogenous energy reserves and supplemented with glutamate or L-lactate. These cells were energetically competent, since they oxidized both substrates, generated an electrochemical proton gradient (deltamuH+) and synthesized ATP via oxidative phosphorylation. Studies with KCN showed that: (i) L-lactate oxidation occurred via two terminal menaquinol oxidases - the ba3-type sensitive to low KCN and the bo-type insensitive to cyanide, (ii) glutamate oxidation proceeded via the bo-type oxidase, and (iii) ATP synthesis with glutamate or L-lactate was coupled only to the bo-type oxidase. Also in glucose-grown cells oxidizing L-lactate, ATP synthesis was coupled to the highly repressed bo-type oxidase. It is suggested that in the respiratory chain of strain 17810R two energy coupling sites may be present: in the complex of NADH-menaquinone oxidoreductase and in the complex of the bo-type menaquinol oxidase. The rate of ATP synthesis was similar with both substrates, but the rate of their oxidation differed significantly: the P/O ratios were 1.5 and 0.03 with glutamate and L-lactate, respectively. CCCP accelerated glutamate oxidation by 50% but was without effect on L-lactate oxidation. In cell lysates, the rates of NADH and L-lactate oxidation were equal. It is concluded that in whole cells of S. aureus 17810R oxidation of NADH derived from glutamate breakdown is tightly coupled to phosphorylation, while L-lactate oxidation seems to be rather loosely coupled.

Physiology and genetics of methylotrophic bacteria

Methylotrophic bacteria comprise a broad range of obligate aerobic microorganisms, which are able to proliferate on (a number of) compounds lacking carbon-carbon bonds. This contribution will essentially be limited to those organisms that are able to utilize methanol and will cover the physiological, biochemical and genetic aspects of this still diverse group of organisms. In recent years much progress has been made in the biochemical and genetic characterization of pathways and the knowledge of specific reactions involved in methanol catabolism. Only a few of the genetic loci hitherto found have been matched by biochemical experiments through the isolation or demonstration of specific gene products. Conversely, several factors have been identified by biochemical means and were shown to be involved in the methanol dehydrogenase reaction or subsequent electron transfer. For the majority of these components, their genetic loci are unknown. A comprehensive treatise on the regulation and molecular mechanism of methanol oxidation is therefore presented, followed by the data that have become available through the use of genetic analysis. The assemblage of methanol dehydrogenase enzyme, the role of pyrrolo-quinoline quinone, the involvement of accessory factors, the evident translocation of all these components to the periplasm and the dedicated link to the electron transport chain are now accepted and well studied phenomena in a few selected facultative methylotrophs. Metabolic regulation of gene expression, efficiency of energy conservation and the question whether universal rules apply to methylotrophs in general, have so far been given less attention. In order to expand these studies to less well known methylotrophic species initial results concerning such area as genetic mapping, the molecular characterization of specific genes and extrachromosomal genetics will also pass in review.