Determination of optimal growth parameters for the bioincising fungus Physisporinus vitreus by means of response surface methodology

To evaluate the influence of water activity (a(w)), temperature and pH on the radial growth and lag phase of Physisporinus vitreus (E-642), a basidiomycete was used in the biotechnological process of bioincising. Radial growth was monitored for 20 days on malt extract agar medium. Five levels of a(w) (0.998, 0.982, 0.955, 0.928, 0.892) were combined with three incubation temperatures (10, 15, 20 degrees C) and three pH values (4, 5, 6). Data analyses showed a highly significant effect of a(w) and temperature (P < 0.0001) and a significant effect of pH (P < 0.05). The radial growth rate and lag phase of P. vitreus were very sensitive to a(w) reduction. Although P. vitreus was able to grow at all the selected temperatures and pH values, the lag phase increased with decreasing a(w) and growth became inhibited at a(w) = 0.955. Optimal conditions for growth of P. vitreus were a(w) = 0.998, 20 degrees C and pH 5. The response surface model provided reliable estimates of these growth parameters and confirmed a greater dependence on a(w) than on temperature or pH under in vitro conditions. Low levels of a(w) can prevent growth of P. vitreus, so wood moisture content should be adjusted accordingly. Implementation of these results should contribute towards the optimization and efficiency of bioincising.