Plasma-mediated enhancement of enzyme secretion in Aspergillus oryzae

Technical bottlenecks in protein production and secretion often limit the efficient and robust industrial use of microbial enzymes. The potential of non-thermal atmospheric pressure plasma to overcome these technical barriers was examined. Spores of the fermenting fungus Aspergillus oryzae (A. oryzae) were submerged in potato dextrose broth (PDB) (5 x 10(6) per ml) and treated with micro dielectric barrier discharge plasma at an input voltage of 1.2 kV and current of 50 to 63 mA using nitrogen as the feed gas. The specific activity of alpha-amylase in the broth was increased by 7.4 to 9.3% after 24 and 48 h of plasma treatment. Long-lived species, such as NO2- and NO3-, generated in PDB after plasma treatment may have contributed to the elevated secretion of alpha-amylase. Observations after 24 h of plasma treatment also included increased accumulation of vesicles at the hyphal tip, hyphal membrane depolarization and higher intracellular Ca2+ levels. These results suggest that long-lived nitrogen species generated in PDB after plasma treatment can enhance the secretion of alpha-amylase from fungal hyphae by depolarizing the cell membrane and activating Ca2+ influx into hyphal cells, eventually leading to the accumulation of secretory vesicles near the hyphal tips.