Water activity, solute and temperature modify growth and spore production of wild type and genetically engineered Aspergillus niger strains

The effect of interactions of water activity (aw) (0.99–0.90), temperature (20, 30 and 35 °C) and modifying aw solute (glycerol, NaCl) on growth and sporulation of a wild-type strain of Aspergillus niger (W) and two genetically engineered lysozyme-producing strains (L11, B1) was examined for the first time. Maximum growth rates were achieved for both strains (L11 and B1) under moderate aW levels. L11 showed a higher growth rate than B1. Fastest growth was achieved at 30 °C, using glycerol as solute. Optimum conditions for growth of strain L11 were estimated by means of contour plot surfaces and found to be 0.965 aw with glycerol as solute at 35 °C. The predicted value of the optimum growth rate was 10.5 mm/day. A value of 10.85 mm/day was obtained experimentally giving a good correlation between the estimated and the measured results. Sporulation was optimum for the W strain at 0.99–0.95 by B1 at 35 °C. Significant higher production of conidia by L11 at 0.97–0.93 aw and at 0.97 aw and 35 °C for B1 strain was observed. Optimum conditions for spore production were different from those for growth. Under similar ecological conditions, the W and both the genetically engineered strains had a different growth and sporulation pattern.