An investigation of biphasic growth kinetics for Phanerochaete chrysosporium (BKMF-1767) immobilised in a membrane gradostat reactor using flow-cells

A novel membrane gradostat reactor (MGR) was patented in 1999. This MGR is used for the continuous production of secondary metabolites, such as lignin peroxidase and manganese peroxidase, from an immobilised biofilm of Phanerochaete chrysosporium, in response to nitrogen starvation. Extensive research has been done previously on the biochemistry and the enzymatic activities of this fungus, but very little information is available on this fungus’ growth kinetics and nutrient consumption, within a continuously operated MGR system. It was the purpose of this study to identify the biofilm growth phases and to quantify the growth kinetics and nutrient consumption of an immobilised biofilm of P. chrysosporium (BKMF-1767) using single-capillary flow-cell MGR's, operated under different spore concentrations and airflow rates. Biofilm thickness increased with an increase in both spore concentration and airflow rate. Biphasic growth (first and second exponential growth phases, separated by a short intermediate lag phase) was demonstrated. For the first exponential growth phase, the biofilm thickness increase rate (kf) ranged between 0.07 and 0.1 h−1 and for the second exponential growth phase the growth slowed down to between 0.015 and 0.05 h−1. The ammonium depletion of 96–99% corresponded to the time of the intermediate lag phase. At the end of the first exponential growth phase, the glucose depletion was approximately 13%, compared to 24% during the second exponential growth phase. For this system, the intermediate lag phase occurred in response to the ammonium depletion and not glucose depletion. The fungal growth was accompanied by pH acidification, attributed to NH4+/H+ exchange, only up to the time of ammonium depletion. The determination of the biofilm thickness increase rate, kf, for biphasic growth, in relation to glucose and ammonium consumption, for within a MGR system, was not previously reported.