The filamentous fungus Aspergillusniger is a kind of important industrial fermentation microorganisms, and widely used in industrial enzymespreparation and organic acid fermentation. It is the main bacteria strain to produce gluconic acid, and gallic acid, particularly citric acid. The production of citric acid is more than 1.5 million tons a year. Meanwhile, more than 99% of citric acid is produced by the fermentation of Aspergillus niger.
In recent years, scientists constantly found Aspergillusniger can produce a variety of secondary metabolites. The number of different secondary metabolites being identified is more than 140.Many secondary metabolites are considered to be safe and have extensive application in food, feed and biotechnology industry. However, Aspergillusniger genetic transformation system is not perfect as the scientists hope. The gene knockout of Aspergillus niger is the prevalence research method and target in current filamentous fungi research field.
Preliminary study found that Nonhomologous end-joining (NHEJ) which has dominant effect on non-homologous recombination inFilamentous fungi dominant (NHEJ) play aleading role in double-strand break repair，and the effect of homologous recombination is negligible. Therefore, the homologous recombination rate is very low.
Recently, JibinSunresearch group of Tianjin Institute of Industrial Biotechnology Chinese Academy of Sciences(TIB,CAS)have designed a method about markerless deletion of linear fragment gene. They utilize positive and negative selection marker strategy and successfully achieve the markerless deletion of linear fragment gene of Ku70 which is closely related with NHEJ in Citric acid producing strains which is provided by Biochemical (AnHui) Co., Ltd.,(hereinafter called COFCO Biochemical). The efficiency of Homologous recombination improves dozens of times than before.
Currently, the research Group has signed a cooperation agreement about Citric Acid Producing Strains building with COFCO Biochemical, and established the important research strategic cooperative partnership. This research was supported by the National Natural Science Foundation of China(30870574).
