[Glucoamylase enhancement regulated by blue light in Aspergillus niger]

Regulation of glucoamylase production in photoinduced A. niger under blue light were investigated. The results showed that continuous illumination of blue light was effective in promotion of conidiation, leading to more glucoamylase production due to the need of sporulation in A. niger. It was clear that 36h-old mycelium grown in dark was in the developmental stage of formation of conidiophore stalk and was most sensitive to BL A. niger cultures exhibited some competence stage to respond to blue light over a period of 36 h when early conidiophore stalk formed in darkness, and photoinduction at this critical period resulted in relatively higher yield of glucoamylase. The fluence-response data generated with blue light indicated that the optimum fluence required for the photomorphogenetic response in A. niger was no less than 450 (mol/m2 x s) to saturate the photoinduction system. The amount of glucoamylase gene (G1) transcripts accumulated during illumination with blue light was more than that in total darkness, whereas the threshold for G1 induction during illumination with increased gradient light was higher than that exposed directly to light of constant fluence, indicating the existence of a light adaptation mechanism for glucoamyalse production in response to blue light. Nevertheless, both high and low light were able to promote glucoamylase producing. Furthermore, suppression subtractive hybridization experiment revealed that some respiratory chain redox enzymes in mitochondria including alternative oxidase as well as sulfhydryl oxidase participated the photoresponse in A. niger and consequently influenced the metabolism. The results support a possibility of designing strategies to improve glucoamylase yield by application of blue light.