[Effectiveness of expression of tdh gene of Vibrio parahaemolyticus depends on two point mutations in promoter region].

A molecular-biological study of the clinical strains of Vibrio parahaemolyticus that contain genes of thermostable direct hemolysin Tdh) and Tdh-related hemolysin (Trh). Using Southern blot hybridization, it is shown that genomes of strains that carry determinants of both hemolysins (tdh(+)-trh+) represent a single copy, whereas in tdh2+RH+ strains, there are two copies (tdh1 and tdh2). All of the examined tdh+trh+ and some of the tdh+trh strains either did not express the tdh gene or did not express the tdh gene (Kanagawa negative or KP-) or expressed it weakly and not often (Kanagawa intermediate, KP+), unlike several Kanagawa positive tdh+trh- strains. To establish the reasons for KP -/+ phenotypes, tdh, tdh11, and tdh2 genes of 13 strains isolated in Russia and neighboring foreign countries were sequenced, followed by the biotransformation analysis of the obtained sequences, as well as a comparison with those of a number of strains presented in GenBank. The results revealed that the weak expression of the tdh gene depends, not only on one point mutation in the promoter region (substitution of A for G in the -35 region), as was thought previously, but also on the second substitution (G for A in the -3 position relative to the -10 sequence), which is quite sufficient when the former is absent. Therefore, the reversion of KP -/+ strains that contain one of these substitutions can take place as a result of a single reverse point mutation, and they should be considered potentially dangerous. Strains that contain both substitutions may revert with lesser probability because, in this case, both mutations are necessary.