Production of alpha-Amylase by the Ruminal Anaerobic Fungus Neocallimastix frontalis.

alpha-Amylase production was examined in the ruminal anaerobic fungus Neocallimastix frontalis. The enzyme was released mainly into the culture fluid and had temperature and pH optima of 55 degrees C and 5.5, respectively, and the apparent K(m) for starch was 0.8 mg ml. The products of alpha-amylase action were mainly maltotriose, maltotetraose, and longer-chain oligosaccharides. No activity of the enzyme was observed towards these compounds or pullulan, but activity on amylose was similar to starch. Evidence for the endo action of alpha-amylase was also obtained from experiments which showed that the reduction in iodine-staining capacity and release in reducing power by action on amylose was similar to that for commercial alpha-amylase. Activities of alpha-amylase up to 4.4 U ml (1 U represents 1 mumol of glucose equivalents released per min) were obtained for cultures grown on 2.5 mg of starch ml in shaken cultures. No growth occurred in unshaken cultures. With elevated concentrations of starch (>2.5 mg ml), alpha-amylase production declined and glucose accumulated in the cultures. Addition of glucose to cultures grown on low levels of starch, in which little glucose accumulated, suppressed alpha-amylase production, and in bisubstrate growth studies, active production of the enzyme only occurred during growth on starch after glucose had been preferentially utilized. When cellulose, cellobiose, glucose, xylan, and xylose were tested as growth substrates for the production of alpha-amylase (initial concentration, 2.5 mg ml), they were found to be less effective than starch, but maltose was almost as effective. The fungal alpha-amylase was found to be stable at 60 degrees C in the presence of low concentrations of starch (</=5%), suggesting that it may be suitable for industrial application.