Nitrogen dependence of cellulase and hemicellulase activities in lignocellulose degrading microbial communities

Sequential enrichment methods have been used to discover industrially relevant microorganisms and enzymes for lignocellulose deconstruction.  This study focused on determining if the thermophilic microbial community enriched on municipal green waste, a potential feedstock for lignocellulosic biofuel production, is nitrogen limited and, if so, what the optimal nitrogen level might be for maximum secretion of enzymes.  Six levels of added nitrogen were examined.  Samples of green waste were wetted to 80% wet basis moisture content.  M9 minimal medium, to which 0-5 g/L NH₄Cl was added, was used as the sole initial wetting agent.  An established thermophilic community was introduced as inoculum and samples were allowed to enrich aerobically at 55˚C for one week during which CO₂ respiration was monitored.  Enzymes were extracted and cellulase and hemicelluase activities were assayed using the DNS reducing sugar assay.  The results showed a strong correlation between added NH₄Cl and enzyme activity.  Both cellulase and hemicellulose activity were greatest at 3 g/L NH₄Cl showing a 220% and 325% increase in enzyme activity, respectively, as compared to the standard M9 nitrogen level of 1 g/L NH₄Cl.  16S rRNA gene sequencing data will be used to elucidate the impact of nitrogen level on microbial communities responsible for increased enzyme production.