Nine strains of lactic acid bacteria that hydrolyze starch were isolated from burong isda, an indigenous fermented food made from fish and rice in the Philippines. Conventional taxonomic and DNA-DNA reassociation studies indicated that all these isolates belong to Lactobacillus plantarum. Each of these isolates harbored more than ten plasmid species with molecular sizes of 2 to 60 kb. The amylolytic activity of L137, one of the isolates, was lost by treatment with novobiocin at 43% frequency, concomitant with curing of a 33-kb plasmid, pLTK13; this suggested that pLTK13 carries a gene necessary for synthesis of amylolytic enzyme. An acidophilic starch-hydrolyzing enzyme secreted from L137 cells was purified 46-fold with specific activity of 44 units per mg protein. The enzyme was shown to have a molecular mass of about 230 kDa and the optimum temperature and pH for the enzyme reaction with soluble starch were 35 degrees C and 3.8-4.0, respectively. The enzyme hydrolyzed soluble starch, amylopectin, glycogen, and pullulan, and to a small extent amylose, while it exerted no activity on dextran and cyclodextrins. The major reaction products from soluble starch were maltotriose, maltotetraose and maltopentaose, but no panose was detected, and maltotriose was the sole product from pullulan. The K-m values for soluble starch, pullulan, and amylose were 4.0, 5.1, and 33 g per liter, respectively. These observations suggest that this enzyme hydrolyzes both alpha-1,6- and alpha-1,4-glucosidic linkages.