Polymorphism in Escherichia coli: rtl atl and gat Regions Behave as Chromosomal Alternatives

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Abstract
Among 40 wild strains of E. coli, 16 utilized galactitol (as did strain K12) and 7 utilized ribitol (as did strain C) of which 6 utilized D-arabitol; none utilized all 3 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. The mapping of gat+ (Lengeler, 1977) and rtl+ atl+ (Reiner, 1975) were confirmed and extended 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.