IDENTIFICATION AND CHARACTERIZATION OF THE PQQDGC GENE-CLUSTER INVOLVED IN PYRROLOQUINOLINE QUINONE PRODUCTION IN AN OBLIGATE METHYLOTROPH METHYLOBACILLUS-FLAGELLATUM

Pyrroloquinoline quinone is a prosthetic group of bacterial methanol d ehydrogenases as well as some alcohol and glucose dehydrogenases. Gene s involved in pyrroloquinoline quinone production have previously been cloned from the representatives of the alpha and gamma subdivisions o f the Proteobacteria. We report identification and the sequence of the pqqDGC gene cluster in the obligate methylotroph, Methylobacillus fla gellatum, which belongs to the beta subdivision. The deduced products of the pqq genes from M. flagellatum appear to be more similar to thei r counterparts from non-methylotrophic species of the gamma subdivisio n than to a facultative methylotroph of the a subdivision. A non-polar mutation in pqqG was constructed and resulted in a strain impaired in growth on methanol. This mutant accumulated a detectable amount of in tracellular pyrroloquinoline quinone, but in contrast to the wild type , did not excrete pyrroloquinoline quinone into the culture medium. Th e possible role of PqqG is discussed.