Biofilm productivity and concomitant cell autolysis in a membrane bioreactor

Phanerochaete chrysoporium morphology and manganese peroxidase (MnP) productivity was characterised in a scalable, modularised 1145 cm³ membrane gradostat reactor in response to switching between an enhanced production medium and a nutrient limited feed (50% C and N reduction). Irrespective of the feed composition used nutrients permeating from the lumen of the ultrafiltration membrane matrix established nutrient gradients across the immobilised biofilm with distinct primary, stationary and decline growth phases observed. Severe nutrient C and N limitation did not change the cyclic nature of enzyme production (MnP_max = 189.5 U l⁻¹) but did reduce the overall bioreactor efficiency from 32 to 22 U l⁻¹ day⁻¹. Stress induced secondary metabolism resulted in concomitant cell autolysis causing biomass loss and increased operational flux after 20 days in the 33 day bioreactor operation cycle.