Effect of magnesium and some nutrients on the growth and nuclease formation of a moderate halophile, Micrococcus varians var. halophilus.

Production of halophilic nuclease by a moderate halophile, Micrococcus varians, ATCC 21971, was maximal at 2.5 to 3.5 M NaCl concentration in a complex medium (CM) composed of 1% casamino acids, 1% yeast extract, and NaCl. The addition of 81 mM MgSO4 to CM inhibited nuclease production in spite of good growth. Microscopic observation showed that this inhibition was accompanied by complete clumping of the cells. The Sehgal and Gibbons complex medium (SGC) which contained 0.75% vitamin-free casamino acids, 1% yeast extract, and NaCl, however, supported good production of the nuclease in spite of the presence of 81 mM MgSO4. It seemed that both magnesium sulfate and some substances present in CM might be responsible for this inhibition and clumping. A synthetic medium optimal for enzyme production was developed consisting of 16 amino acids, 4 vitamins, 0.73 mM KH2PO4, 2.7 mM KCl, 20 mM MgSO4, and 2.5 M NaCl. The organism required biotin as an essential growth factor, and thiamine, riboflavin, and choline as stimulating factors. Omission of isoleucine from the medium reduced markedly the growth rate. Glutamic acid, proline, and arginine were consumed completely during cultivation in the synthetic medium.