A STUDY OF CORNSTARCH GRANULE DIGESTION BY AN UNUSUALLY HIGH-MOLECULAR-WEIGHT ALPHA-AMYLASE SECRETED BY LACTOBACILLUS-AMYLOVORUS

The cells of Lactobacillus amylovorus (NRRL B-4540), grown in a medium containing 2% cornstarch as the sole carbon source, secreted an amylase activity that rapidly solubilized cornstarch. Fourier transform infrared (FTIR) spectroscopic analyses showed that 80-90% of starch was consumed by bacteria in a 10-day-old culture medium. The remnant of starch granules digested in the culture medium inoculated with the cells of L. amylovorus have also lost their characteristic iodine-binding capacity as visualized by starch dye-binding microplate assay and light microscopy. Scanning electron miscroscopy (SEM) of granules from a 48-h culture medium showed hollow and fragmented granules with a pitting phenomenon characteristically produced by alpha-amylase activity. Analysis of an enzyme preparation from a culture medium of L. amylovorus revealed that the putative enzyme appears to be a single protein band of unusually high M(r) (150,000) on SDS gels stained for amylase activity. Analysis of starch digestion products by thin layer chromatography (TLC) showed enzyme activity typical of alpha-amylase.