L-ARABINOSE-RESISTANCE TEST WITH SALMONELLA-TYPHIMURIUM STRAIN SV3 SELECTS FORWARD MUTATIONS AT SEVERAL ARA GENES

A new assay has been described for mutagenicity testing using an l-arabinose-sensitive strain of Salmonella typhimurium. The test strain SV3 and several l-arabinose-resistant mutants selected therefrom are characterized in the present study by 3 different criteria: inhibition of growth by l-arabinose, accumulation of keto-sugars, and activities of the enzymes involved in l-arabinose catabolism. Strain SV3 (ara-531) shows high levels of inducible l-arabinose isomerase (EC 5.3.1.4) and l-ribulokinase (EC 2.7.1.16) activities, but is deficient in l-ribulose-5-phosphate 4-epimerase (EC 5.1.3.4), the enzyme encoded in Escherichia coli by gene D in the araBAD operon. Addition of l-arabinose to SV3 growing in glycerol or casamino acids stops growth. d-Glucose only partially reverses this inhibition. Reversion of the ara-531 mutation restores different levels of epimerase activity and resistance to l-arabinose. However, the great majority of the l-arabinose-resistant mutants do not utilize l-arabinose. The physiological and enzymatic properties of these l-arabinose non-utilizing mutants suggest that l-arabinose resistance is due to forward mutations in at least 3 other genes, araA, araB and araC, blocking steps prior to l-ribulose 5-phosphate accumulation. © 1979.