SYNTHESIS AND LYSIS OF FORMATE BY IMMOBILIZED CELLS OF ESCHERICHIA-COLI

Formate hydrogenlyase (FHL) activity was induced in a strain of Escherichia coli S13 during anaerobic growth in yeast extract-tryptone medium containing 100 mM formate. The cells obtained at the optimum growth phase were immobilized in 2.5% (w/v) agar gel when 50-60% of the whole cell FHL activity was retained. The immobilized FHL system had good storage stability and recycling efficiency. In the lysis of formate, an increase of formate concentration to 1.18M increased QH2 (initial) value of the immobilized cell, and subsequent increase of formate concentration to 2.94M did not significantly lower the QH2 (initial) value. In the lysis of formate by the immobilized cells, hydrogen evolution, in general, ceased after 6 to 8 h of incubation, resulting in incomplete lysis of formate. Presence of small amount of glucose (28 mM) had excellent stimulatory activity on formate lysis. Formate (up to 1.18 M) was more or less quantitatively lysed with concomitant disappearence of glucose from the medium. Synthesis of formate from hydrogen and bicarbonate solution by the immobilized cells was also characterized. Presence of glucose (10 mM) in 50 mM bicarbonate solution stimulated formate synthesis by immobilized cells. The pH optimum range, K(m), and specific activity of the immobilized cells for the lysis of formate were 6.8-7.2, 0.4M, and 66 mL/g cell-h, respectively. The cells could fix hydrogen to the extent of 24.4% (w/w) of its own wet cell mass in a 72-h reaction cycle. Potentially of the immobilized FHL system for biotechnological exploitation was discussed.