Technical Abstract: Composted manure from a dairy farm in Texas was examined for thermophilic microorganisms by enrichment in xylose broth medium. Forty randomly picked isolates were identified as strains of Bacillus coagulans by sequence analysis of rRNA genes. One strain, designated as MXL-9, could convert mixed sugars of glucose, xylose, and arabinose to L-lactic acid with 85% yield at pH 6.0 and 50°C. The strain was tolerant to aldehyde growth inhibitors, with no difference in optical density observed in the presence of 2.5 g/l of either furfural or 5-hydroxymethylfurfural, and 4-hydroxybenzaldehyde (1.2 g/l), and vanillin (2.5 g/l) reducing the optical density to only 78% and 87%, respectively, of untreated controls. In a simultaneous saccharification and fermentation process, strain MXL-9 converted a dilute-acid hydrolysate of 100 g corn fiber/l to 39 g lactic acid/l in 72 h at 50°C. Because of its inhibitor tolerance and ability to fully utilize xylose and arabinose, B. coagulans strain MXL-9 has potential to be developed as a biocatalyst for the conversion of agricultural residues into valuable chemicals.