Protease and lipase production by a strain ofSerratia marcescens (532 S)

Summary Production of both exolipase and exoprotease activities bySerratia marcescens 532 S isolated from an aerobic fixed-biomass reactor were strongly influenced by nutritional factors which acted as inducers or repressors. In batch culture, protease and lipase activities were produced after the exponential phase. NH₄Cl, amino acids and simple carbon sources caused repression of protease activity. At a concentration of 1.5 g L^–1, the individual addition of maltose, mannitol, acetate, fructose or glucose, repressed exoprotease production, with the greatest effect by glucose. An inverse relationship existed between exoprotease synthesis and increasing glucose concentrations. Lipids activated lipase production, the most significant increase occurred when Tween 80 was added in the medium. Thus, glucidolytic, proteolytic and lipolytic activities could be efficiently expressed in batch cultures only successively.At low dilution rate of chemostat cultures with a constant glucose input concentration of 2 g L^–1, glucidolytic, proteolytic and lipolytic activities were produced, but did not have the same regulation: atD values <0.08 h^–1, the level of protease activity dropped while that of lipase showed a corresponding increase. Above these values, increasingD led to a decrease of the two hydrolase activities, at the level of the specific activities as well as in the specific rate of biosynthesis of each enzyme. Similar results were obtained in chemostat culture with a constant specific growth rate of 0.04 h^–1 with increasing glucose input concentrations, i.e. protease and lipase activities decreased when the specific glucose uptake rates were enhanced.     

Effect of oxygenation and sulfate concentrations on pyruvate and lactate formation inKlebsiella oxytoca ZS growing in chemostat cultures

Klebsiella oxytoca ZS fermented glucose to ethanol and lactic, formic, and acetic acids, but, in contrast to many strains, accumulates pyruvic and acetic acids as the principal end products in aerobic growth conditions. This strain was grown in sulfate-limited chemostat at a fixed low dilution rate (D=0.033 h^–1) with glucose present in excess. When oxygen was supplied at a high level, pyruvate and acetate were produced, and the ratio NADH/NAD⁺ was low (0.04) while the internal pyruvate concentration increased to 100 mol (g dry wt)^–1. A shortage of oxygen supply was accompanied by lactate production, an increase of the ratio NADH/NAD⁺ (0.53), and an undetectable level in internal pyruvate concentration. The observed changes in LDH activity found in vitro in extracts of the cells are not strictly related to those found in vivo. In fact, the specific activity of LDH was essentially stable at 30% of dissolved oxygen tension (d.o.t.) and decreased slightly at 60% of d.o.t., whereas specific lactic acid production decreased rapidly. The in vitro LDH activity was strongly affected by the NADH/NAD⁺ ratio.