Ligninolytic enzyme system of Phanaerochaete chrysosporium: synthesized in the absence of lignin in response to nitrogen starvation

TLDR

The study examined how nitrogen assimilation and growth in stationary batch cultures of *Phanerochaete chrysosporium* relate to the onset of ligninolytic activity under lignin‑optimized conditions. Ligninolytic activity appears after nitrogen depletion, is independent of lignin presence, and is delayed or temporarily suppressed by added ammonium, indicating that the enzyme system is synthesized as a secondary metabolic response to nitrogen starvation.

Abstract

The relationship between growth, nutrient nitrogen assimilation, and the appearance of ligninolytic activity was examined in stationary batch cultures of the wood-destroying hymenomycete Phanerochaete chrysosporium Burds. grown under conditions optimized for lignin metabolism. A reproducible sequence of events followed inoculation: 0 to 24 h, germination, linear growth, and depletion of nutrient nitrogen; 24 to 48 h, cessation of linear growth and derepression of ammonium permease activity (demonstrating nitrogen starvation); 72 to 96 h, appearance of ligninolytic activity (synthetic 14C-lignin leads to 14CO2). Experiments with cycloheximide demonstrated that appearance of ligninolytic activity occurs irrespective of the presence of lignin; lignin did not induce additional activity. Addition of NH4+ to cultures immediately prior to the time of appearance of the ligninolytic system delayed its appearance, suggesting that the NH4+ led to interference with synthesis of the enzyme system. Addition of NH4+ to ligninolytic cultures resulted in an eventual, temporary decrease in ligninolytic activity. The results suggest that all or essential protein components of the ligninolytic enzyme system are synthesized as part of a series of physiological ("secondary metabolic") events that are initiated by nutrient nitrogen starvation.