BIOCHEMICAL AND GENETIC ANALYSIS OF ISOLEUCINE AND VALINE BIOSYNTHESIS IN STAPHYLOCOCCUS AUREUS

After a prototrophic strain of S. 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.