Factors affecting virulence of Shigella flexneri: avirulent strain with altered metablism of succinate, fumarate, and malate.

It has been found that a mutation of Shigella flexneri 2a to avirulence can result in altered metabolism of tricarboxylic acid cycle acids, but the effect is strongly dependent on growth conditions. Mutant cells harvested from stationary-phase cultures grown with vigorous shaking in nutrient broth oxidize succinate, fumarate, and malate much more slowly than do wild-type cells. Cell-free extracts from such cells show similar differences in oxidative ability. These differences were less pronounced when cells were harvested from the exponential phase of growth and were nonexistent when the cells were grown without shaking. When tricarboxylic acid cycle acids were used as carbon sources with shaking, mutant cells from exponential phase cultures oxidized tricarboxylic cycle acids almost to the same extent as the wild type. Stationary-phase cells grown on succinate lost succinoxidase activity, but wild-type cells retained more than twice the activity of mutant cells. The effect of growth conditions on oxidative differences between the two strains was similar to the differences in succinate uptake observed under similar conditions.