Cloning and Expression of Cellulosome-Integrating Protein from Aspergillus niger H1 Improves Phosphate Solubilization

A primary cDNA library of Aspergillus niger H1 was constructed using SMART (switching mechanism at the 5' end of RNA transcript) technique. A total of 169 clones had halos on the insoluble phosphate medium, and clone H-47 had clear halos. The full-length cDNA of clone H-47 was 625 bp, with a complete open reading frame (ORF) of 390 bp, encoding a protein of 129 amino acids. Multiple alignment revealed a high degree of homology between the ORF of the clone and other fungi cellulosome-integrating protein (CipC-like). The expression vector of ORF was constructed and transformed into Escherichia coli DH-5a. The transformant (ORF-1) with the CipC-like gene secreted more organic acid when grown in tricalcium phosphate (TCP) medium, with TCP as the sole source of phosphate. E. coli DH5a containing the cipc-like gene secreted methanoic acid, acetic acid, malic acid, and citric acid reached 81.2, 93.3, 50.6, and 147.7 ug mL-1, respectively, within 28 h. These results showed that the expression of the A. niger H1 CipC-like gene in E. coli could enhance organic acid secretion and improve phosphate solubilizing ability.