A strain of Bacillus coagulans that converted mixed sugars of glucose, xylose, and arabinose to l-lactic acid with 85% yield at 50A degrees C was isolated from composted dairy manure. The strain was tolerant to aldehyde growth inhibitors at 2.5 g furfural/l, 2.5 g 5-hydroxymethylfurfural/l, 2.5 g vanillin/l, and 1.2 g p-hydroxybenzaldehyde/l. In a simultaneous saccharification and fermentation process, the strain converted a dilute-acid hydrolysate of 100 g corn fiber/l to 39 g lactic acid/l in 72 h at 50A degrees C. Because of its inhibitor tolerance and ability to fully utilize pentose sugars, this strain has potential to be developed as a biocatalyst for the conversion of agricultural residues into valuable chemicals.