Abstract: Seven cellulase-producing strains having large Congo red hydrolysis halo（D）and colony D/H（H is colony diameter of a strain）were isolated from soil samples containing rotten straws. Strain S-1 presented the highest CMCase activity of decomposing carboxymethylcellulose sodium，and was identified as Bacillus amyloliquefaciens. Ion beam mutagenesis was performed on S-1，and mutant strains with increased CMCase activity were screened out by high-throughput enzyme activity assay. Total 15 mutant strains with high CMCase activities after culturing for 5 generations were obtained. Among these strains，mutant strain 308，which showed totally different colony morphology，performed the highest CMCase activity. Its CMCase activity increased 84.4% after culturing for 24 h，compared to the CMCase activity of S-1；moreover，the increased CMCase activity was genetically stabile，indicating that ion beam mutagenesis has potential application value for improving the cellulase production capability of a strain.

Key words: Bacillus amyloliquefaciens, ion beam, mutagenic breeding, cellulase activity