Pedersen H, Christensen B, Hjort C, Nielsen J
Center for Process Biotechnology, Department of Biotechnology, Technical University of Denmark, Lyngby.
Metab Eng. 2000 Jan;2(1):34-41. doi: 10.1006/mben.1999.0136.
Aspergillus niger produces oxalic acid as a by-product which causes problems with downstream processing of industrial enzymes. To overcome this problem the oah gene encoding oxaloacetate hydrolase (EC 3.7.1.1) was disrupted in a glucoamylase-producing strain of A. niger and the resulting strain was incapable of producing oxalic acid. The strain with the disrupted gene was compared with the wild-type strain producing oxalic acid in batch cultivations. The specific growth rate of both strains was 0.20 h(-1). The citric acid yields were identical, but the glucoamylase yield was only 50% in the disruptant compared with the wild-type strain. Batch experiments with 13C-labeled glucose as substrate were carried out to determine the metabolic fluxes through the central metabolism. The two strains had almost identical metabolic fluxes, which suggested that it was possible to disrupt the oah gene without pleiotropic consequences. The flux through the pentose phosphate pathway was around 60% of the glucose uptake for both strains, which suggested that a sufficient supply of NADPH was available for biosynthesis.
黑曲霉会产生草酸作为副产物，这给工业酶的下游加工带来了问题。为克服这一问题，在一株产糖化酶的黑曲霉中破坏了编码草酰乙酸水解酶（EC 3.7.1.1）的oah基因，所得菌株无法产生草酸。将该基因被破坏的菌株与在分批培养中产生草酸的野生型菌株进行比较。两种菌株的比生长速率均为0.20 h⁻¹。柠檬酸产量相同，但与野生型菌株相比，破坏菌株中的糖化酶产量仅为50%。以¹³C标记的葡萄糖为底物进行分批实验，以确定通过中心代谢的代谢通量。这两种菌株具有几乎相同的代谢通量，这表明有可能破坏oah基因而不产生多效性后果。两种菌株通过磷酸戊糖途径的通量约为葡萄糖摄取量的60%，这表明有足够的NADPH供应用于生物合成。
