Studies on Cellular Response of Escherichia coli to UDP-Galactose Accumulation

Cellular responses to intracellular accumulation of UDP-galactose (UDP-Gal) were investigated for D-galactose-induced lysis of an Escherichia coli galE mutant. The mutant, ara-207, showed dramatic lysis in a nutrient broth supplemented with D-galactose after 3h of cultivation when transformation of normal rod cells into bulged- and spheroplast-like cells was clearly observed under electron microscope. UDP-Gal had been already detected with the optimal level at 2 h of cultivation, followed by a drastic decrease in its level as well as a significant increase in the level of active (inhibitor-free) UDP-sugar hydrolase (USH) together with the bacterial lysis. Significant loss of UTP, UDP, and UDP-N-acetylglucosamine agreed with the in vivo activity of USH thus produced. Addition of D-sorbitol did not restrict UDP-Gal accumulation but did mostly protect ara-207 against the above morphological changes of the cells in which overproduction of USH was repressed over 3 to 4 h of cultivation. These results suggested that accumulation of UDP-Gal could have some growth inhibitory effect on E. coli cells but the compound was not directly involved with the following lytic process via spheroplast formation. A possibility was taken into account, that the accumulation of UDP-Gal caused overproduction of USH, which may provoke inhibition of bacterial peptidoglycan synthesis.