ABSTRACT
A well-known industrial fungus for enzyme production, Aspergillus niger, was selected to produce the feruloyl esterase FAEA by homologous overexpression for pulp bleaching application. The gpd gene promoter was used to drive FAEA expression. Changing the nature and concentration of the carbon source nature (maltose to glucose; from 2.5 to 60 g l(-1)), improved FAEA activity 24.5-fold and a yield of 1 g l(-1) of the corresponding protein in the culture medium was achieved. The secreted FAEA was purified 3.5-fold to homogeneity in a two-step purification procedure with a recovery of 69%. The overproduced protein was characterised and presented properties in good agreement with those of native FAEA. The recombinant FAEA was tested for wheat straw pulp bleaching, with or without a laccase mediator system and xylanase. Best results were obtained using a bi-sequential process with a sequence including xylanase, FAEA and laccase, and yielded very efficient delignification--close to 75%--and a kappa number of 3.9. This is the first report on the potential application of recombinant FAEA in the pulp and paper sector.
Subject(s)
Aspergillus niger/enzymology , Carboxylic Ester Hydrolases , Industry , Paper , Aspergillus niger/genetics , Biotechnology/methods , Carboxylic Ester Hydrolases/chemistry , Carboxylic Ester Hydrolases/genetics , Carboxylic Ester Hydrolases/isolation & purification , Carboxylic Ester Hydrolases/metabolism , Endo-1,4-beta Xylanases/metabolism , Genetic Vectors , Laccase/metabolism , Recombinant Proteins/chemistry , Recombinant Proteins/isolation & purification , Recombinant Proteins/metabolism , Transformation, Genetic , Triticum/metabolismABSTRACT
A two-step bioconversion process of ferulic acid to vanillin was elaborated combining two filamentous fungi, Aspergillus niger and Pycnoporus cinnabarinus. In the first step, A. niger transformed ferulic acid to vanillic acid and in the second step vanillic acid was reduced to vanillin by P. cinnabarinus. Ferulic acid metabolism by A. niger occurred essentially via the propenoic chain degradation to lead to vanillic acid, which was subsequently decarboxylated to methoxyhydroquinone. In 3-day-old cultures of P. cinnabarinus supplied with vanillic-acid-enriched culture medium from A. niger as precursor source, vanillin was successfully produced. In order to improve the yields of the process, sequential additions of precursors were performed. Vanillic acid production by A. niger from ferulic acid reached 920 mg1-1 with a molar yield of 88% and vanillin production by P. cinnabarinus from vanillic acid attained 237 mg1-1 with a molar yield of 22%. However, the vanillic acid oxidative system producing methoxyhydroquinone was predominant in P. cinnabarinus cultures, which explained the relatively low level in vanillin.
