Heterologous protein secretion from Aspergillus niger in phosphate-buffered batch culture

Abstract

Aspergillus niger was grown in batch culture containing various initial concentrations of sodium phosphate buffer (pH 6.5). A wild-type strain of A. niger and a transformed strain producing hen egg-white lysozyme were studied. The maximum cell yield was attained in medium not supplemented with phosphate. In those cultures acidification of the medium resulted in a minimum of pH 2.0 before reverting to near neutrality. Increasing the initial levels of phosphate buffer reduced the fall in pH but lowered cell yields. Secreted levels of lysozyme were maximal in the 50–100 mm range of added phosphate buffer although mycelial yields were reduced by one third of mycelial yields in medium unsupplemented with phosphate buffer.