Improved glucoamylase production by Rhizopus sp. A-11 using metal-ion supplemented liquid medium

Abstract

Rhizopus sp. A-11 produced glucoamylase (GA, EC 3.2.1.3) to a high concentration in a basal liquid medium supplemented with zinc and calcium ions. Since zinc ions were essential for the growth of the organism, supplementation of zinc ions in the medium was essential for the growth and GA production of Rhizopus sp. A11. In addition of zinc ions, supplementation of calcium ions stimulated GA production. Supplementation of the basal liquid medium with 0.7 ppm (w/v) zinc ions and 75 ppm calcium ions was approximately resulted in GA production of 650 units per ml. Based on the activity per mg-protein, this activity was 4.6 times that recorded for extract from a conventional solid state culture of the same Rhizopus sp. A11 on wheat bran medium. Almost all of the protein secreted into the liquid culture medium was GA and this resulted in a high specific activity of GA (4,040 units/mg-protein). The results presented in this paper indicate that liquid culture of Rhizopus sp. A-11 in a basal medium supplemented with zinc and calcium ions is an efficient method for GA production with high specific activity.