gdhB, a gene encoding a second quinoprotein glucose dehydrogenase in Pantoea citrea, is required for pink disease of pineapple

The pink disease of pineapple, caused by the bacterium Pantoea citrea, is c haracterized by a dark coloration on fruit slices after canning. A glucose dehydrogenase (Gdh) encoded by the gdhA gene has been implicated in the col our formation activity of P. citrea. In this paper it has been shown that P . citrea contains a second, homologous gdh gene and its product, GdhB, repr esents the main source of Gdh activity in this organism. Unlike gdhA, gdhB is constitutively expressed during the exponential phase of growth and is i nduced in stationary phase. A previously isolated chemical mutant, CMC6, wh ich is deficient in Gdh activity and pink disease formation, failed to expr ess gdhB during the stationary phase of growth. The CMC6 mutant can be comp lemented by a 54 bp DNA fragment located upstream of gdhA. This fragment, w hich contains an operator-like II bp inverted repeat, strongly enhances the expression of gdhA, probably by titrating away a negative effector of its expression. These results illustrate the complex interplay operating betwee n the two gdh genes and emphasize the role of glucose metabolism in the pat hway leading to pink disease.