Physiological changes and alk gene instability in Pseudomonas oleovorans during induction and expression of alk genes

The alk genes of Pseudomonas oleovorans, which is able to metabolize alkanes and alkenes, are organized in alkST and alkBFGHJKL clusters, in which the expression of alkBFGHJKL is positively regulated by AlkS. Growth of the wild-type strain GPo1 and P. oleovorans GPo12 alk recombinants on octane resulted in changes of cellular physiology and morphology. These changes, which included lower growth rates and a reduction of the number of CFU due to filamentation, were also seen when the cells were grown on aqueous medium, and the alk genes were induced with dicyclopropylketone, a gratuitous inducer of the alk genes. These effects were seen only for recombinants carrying both alkST and alkBFGHJKL operons. Deletion of parts of either alkB or alkJ, which encode two major Alk proteins located in the cytoplasmic membrane, modified but did not eliminate the effects described above, suggesting that they were due to induction and expression of several alk genes. Continuous growth of the cells in the presence of dicyclopropylketone for about 10 generations led to inactivation, but not elimination, of the alk genes. This resulted in a return of the recombinants to normal physiology and growth.