Biochemical and genetic analysis of isoleucine and valine biosynthesis in Staphylococcus aureus.

After a prototrophic strain of Staphylococcus aureus had been exposed to diethyl sulfate, 28 isoleucine- and isoleucine-valine-dependent mutants (ilv mutants) were isolated. On the basis of auxanography, their ability to accumulate intermediates of isoleucine and valine biosynthesis, and intergeneric syntrophism with ilv mutants of Salmonella typhimurium, all mutants were placed into four groups, each of which corresponded to a presumed enzymatic deficiency, as follows: group A, deficient in l-threonine deaminase; group B, deficient in the condensing enzyme; group C, deficient in reductoisomerase; group D, deficient in alpha-beta-dihydroxy acid dehydrase. No mutants blocked in the terminal (transaminase) reactions were isolated. Transduction analyses (best-fit, ratio, and complementation tests) with the use of phage 83 established that the linear arrangement of the structural genes is identical with the order of participation of their enzymes in isoleucine and valine biosynthesis, and that these genes comprise a single linkage group which can exist on a single donor fragment during transduction.