Improved endoxylanase production and colony morphology of Aspergillus niger DSM 26641 by γ-ray induced mutagenesis

• β-1,4-Endoxylanase activity of Aspergillus niger DSM 26641 was doubled by γ-radiation.
• Restricted widespread filamentous growth on agar plates was observed.
• Miniaturization and pellet surface restriction favors biomass recycling.

Aspergillus niger DSM 26641 was exposed to 60Co γ-radiation to enhance the β-1,4-endoxylanase activity, restrict colony growth and improve robustness of pellets. The first promising mutant obtained after γ-radiation of the fungal spores at 50–2000 Gy showed a restricted colony growth and an 82% enhancement in β-1,4-endoxylanase activity. The mutant was subjected to a second round of γ-radiation at 1400 Gy generating a mutant with double the β-1,4-endoxylanase activity compared to the native strain. The selected final mutant, deposited as A. niger DSM 28712, showed a maximal saccharification activity of 26 U ml−1 on xylan based broth, 48 U ml−1 on lignocellulose hydrolysate and 375 U ml−1 on lignocellulose hydrolysate supplemented with yeast extract and mineral salts.