title: Isolation and characterization of enterotoxin-deficient mutants of Escherichia coli.
abstract: The genes controlling the production of two types of enterotoxin of Escherichia coli, one heat-labile (LT) and the other heat-stable (ST), are found on plasmids. The absence of a direct selection procedure has made it difficult to isolate mutants affecting toxin production. However, the availability of a naturally occurring "recombinant" plasmid, carrying genes for LT and ST formation and also for resistance to tetracycline, streptomycin, and sulfonamides, made it possible to use comutagenesis with N-methyl-N'-nitro-N-nitrosoguanidine to enrich for such mutants. We have isolated and characterized 58 LT- mutants and 7 ST- mutants. Among the LT- group we found amber mutants, temperature-sensitive mutants (most of which produce unusually heat-labile LT), and "leaky" mutants with reduced LT activity. The majority of the tested LT- mutants produced immunologically crossreacting material, in most cases in wild-type amounts. Among all 17 of the LT- mutants that could be transferred, the mutation was found to be on the plasmid. In contrast, only one of four transferrable ST- mutants appeared to be a plasmid mutant.
mesh_terms: D001427:Bacterial Toxins / Q000235:genetics* / Q000276:immunology; D002874:Chromosome Mapping; D003429:Cross Reactions; D004768:Enterotoxins / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics* / Q000302:isolation & purification; D005796:Genes; D009154:Mutation; D010957:Plasmids
chemical_list: D001427:Bacterial Toxins; D004768:Enterotoxins