Polymorphism in Escherichia coli: rtl atl and gat regions behave as chromosomal alternatives

Amongst forty wild strains of Escherichia coli, sixteen utilized galactitol (as did K12) and seven utilized ribitol (as did C) of which six utilized D-arabitol; none utilized all three polyols. Transduction of genes for ribitol utilization (rtl+) to strains able to utilize galactitol (gat+), whether K12 or wild strains, using wild strains and E. coli C as donors always resulted in loss of the galactitol phenotype. The genes for D-arabitol use (atl+) were always cotransduced with rtl+ in interstrain crosses. We confirm and extend the mapping of gat+ (Lengeler, 1977) and rtl+ atl+ (Reiner, 1975) in their respective hosts, K12 and C, by showing both regions to be 50% cotransducible with metG and 3% cotransducible with fpk. In reciprocal transductions, gat+ replaced rtl+ atl+. In partial diploids, rtl+ atl+ and gat+ regions did not interfere with each other's expression. Transfer of rtl+ from an Rtl+ Atl- donor by R plasmid (pE10)-mediated conjugation, gave Gat- transconjugants of K12 in which rtl+ and a kanamycin resistance gene were 100% cotransducible in the metG region of the chromosome. It is suggested that the rtl+ atl+ and gat+ genes (or parts of them) act as alternative, or mutually exclusive, regions in the chromosome. Possible reasons for the existence of alternative characters are discussed.