ISOLATION AND CHARACTERIZATION OF A MUTANT DEFECTIVE IN ONE OF TWO ISOZYMES OF THE ISOCITRATE DEHYDROGENASE FROM A PSYCHROPHILIC BACTERIUM VIBRIO SP. STRAIN ABE-1

Abstract

Vibrio sp. strain ABE-1 has two types of NADP⁺-isocitrate dehydrogenase (IDH-I and -II: EC 1.1.1.42). A mutant defective in IDH-I was isolated by N-methyl-N′-nitro-N-nitrosoguanidine treatment and a new convenient screening method which can directly detect the IDH-I activity of colonies on the screening plates. The direct detection of the enzyme activity was accomplished by coating the colonies with calcium phosphate gel then dehydrogenating in two steps with different tetrazolium salts. An isolate, strain YF-83, completely lacked IDH-I activity, but retained IDH- II activity at a level similar to the parent strain. Strain YF-83 had the same growth characteristics as the parent strain with regard to nutrient
requirements and growth temperatures. Therefore, it was concluded that IDH-I is not essential for the growth of strain ABE-1.