Analysis of mutations affecting the dissimilation of galactitol (dulcitol) in Escherichia coli K12

Summary

Three mutations clustered at 45.5 min of the genetic map of E. coli K12 have been shown previously (Lengeler, 1975a) to affect specifically galactitol transport via an enzyme II-complex^Gat (gatA) of the PEP dependent phosphotransferase system and a soluble, NAD dependent dehydrogenase (gatD). In the present report data are given further supporting the existence of a gat operon, made up by a control gene gatC and the structural genes gatA and gatD. The enzyme II-complex^Gat is shown to catalyze the formation of galactitol-1-P and the dehydrogenase to catalyze the reversible conversion of galactitol-1-P and D-tagatose-6-P. Loss of a phosphofructokinase activity controlled by the gene pfkA prevents growth on galactitol and concomitantly the formation of D-tagatose-1,6-P₂, while the suppressing mutation pfkB-1 restores a phosphofrucokinase activity and growth on galactitol.

As shown further the erratic growth behaviour of E. coli K12, B and C on galactitol is apparently due to a temperature sensitive ketose-bis-phosphate aldolase inactive at temperatures >35° C. This enzyme reacts with D-tagatose-1,6-P₂ and to a lesser extent with D-fructose-1,6-P₂ and thus is able to suppress fda mutations. It is controlled by a new gene locus kba located within 1 min of the marker argG, remoted from the gat operon and the gene fda. Galactitol dissimilation in E. coli K12 thus seems to be via galactitol-1-P-D-tagatose-6-P-D-tagatose-1,6-P₂ to dihydroxyacetone-P+glyceraldehyde-P, controlled by the genetic loci gatC A D, pfkA, pfkB-1 and kba respectively.