Factors influencing protease production by two Antarctic strains of Stenotrophomonas maltophilia

ABSTRACT

The influence of culture medium buffer capacity, the supplementation of culture medium with L-ala and the requirement of calcium for exoprotease production by Antarctic psychrotrophic Stenotrophomonas maltophilia strains ANT-1-1 and ANT-7-1 were examined. When increasing concentrations of calcium chloride (0 to 0.3 g l-1) were added to culture media, maximum protease production yields increased 70-75 (ANT-1-1) and 50 (ANT-7-1), while biomass levels showed little difference. Calcium was also necessary for optimal activity of proteases. L-ala had no effect on protease production. The reduction in buffer capacity, with the consequent change in external pH, had a positive effect, enhancing protease yields. Secretion of proteases into the medium started at the beginning of the stationary phase, corresponding with a rise in pH values up to pH 8.7 and was maximal at 36 h of culture. These results indicate that the regulation of calcium concentration and buffer capacity and also pH monitoring are factors to be considered when the design of an industrial culture medium and the optimisation of protease production processes using these Antarctic strains are concerned.