The amino acid L-lysine was produced from homoserine auxotrophic and S-(2-aminoethyl)-L-cysteine-resistant mutants of a newly isolated gram-positive methylotrophic bacterium, capable of growth on methanol at 60°C. The temperature optimum for growth was between 50 and 53°C. These aerobic, gram-positive endospore-forming, rod-shaped bacteria required biotin and vitamin B12 for growth. Extracts of the bacteria grown on methanol lacked hydroxypyruvate reductase and contained hexulose 6-phosphate synthase activity. Therefore, these bacteria were considered to be type I methylotrophic bacteria of the genus Bacillus. Fed-batch fermentations resulted in cell densities of 50 g of cell dry weight per liter. Biomass yields on carbon, nitrogen, phosphate, and sulfate were determined. Generation of homoserine auxotrophic and amino acid analog-resistant mutants resulted in L-lysine concentrations of nearly 20 g/liter in fed-batch fermentations.