Phanerochaete chrysosporium: Growth pattern and lignin degradation

Summary

The growth behavior of Phanerochaete chrysosporium was characterized in a bioreactor using chemostat and batch cultivation to optimize an inoculum for lignin degradation during stationary cultivation. The pattern of growth and onset of lignin degradation by cells taken from agitated conditions were compared to the behavior of cells grown under stationary conditions. Under nitrogen-limited growth conditions, the fungus displayed a continuous growth-rest-growth cycle, as visually observed and evidenced by changes in total cell carbohydrate and biomass content, indicating recycling of cell nitrogen. Cells taken from the bioreactor degraded lignin only after a mycelial mat was formed under non-agitated conditions. Formation of the mat occurred during completion of primary growth with cells taken at a dilution rate of 0.09 or 0.10 h⁻¹ and with cells from a 1-day-old batch cultivation, resulting in an onset of lignin degradation after 2–3 days. Cells taken at dilution rates <0.09 h⁻¹ formed the mycelial mat as a result of their secondary growth phase. The onset of this mat formation was related to the average age of the cells. Two- to four-day-old cells from the batch cultivation needed 7–9 days before they started to degrade lignin. The glucose consumption rate in the bioreactor during secondary metabolism was 0.09 g · l⁻¹ · day⁻¹, compared to 1.0 g · l⁻¹ · day⁻¹ under non-agitated conditions. This difference is discussed in reference to lignin degradation.