Optimization of cultural and nutritional parameters for pellet formation by Pleurotus ostreatus

Different morphological forms and growth patterns of filamentous fungi as (mycelia, clumps, and pellets) have been observed in industrial processes. The aim of this study was to optimize and investigate the growth and morphology of Pleurotus ostreatus for fungal pellets formation by modifying various cultivation conditions. Factors such as types of fungal culture media (Kirk’s and Malt extract mediums), temperature (25, 28, 32°C), pH (4.5, 5.5, 6.5), cultivation agitation rate (100–130-150rpm), type of carbon sources, levels of fungal inoculum, the presence of additive agents and trace metals were screened for their effect to formulate two types of pellets (simple and complex (hybrid)). Also activity of two ligninolytic enzymes (laccase, manganese peroxidase) was evaluated in both the simple and complex pellets in modified Kirk’s medium. Among all various factors, pH, agitation rate, preparation of fungal inoculum and appropriate time for adding the carbon sources were detected as the most influential factors. According to the results uniform pellets were formed only at pH 5.5 for both types of pellets. Fungal pellets size showed an inverse correlation with the agitation rate of culture. Moreover the formation of pellets remained unaffected by additive agents except with peptone. Measuring the enzymatic activity (laccase and manganese peroxidase) of fungal pellets also revealed that complex pellets have more capability to secrete remarkable amounts of such lignin-degrading enzymes in compared to simple pellets. Based on evidences, fungal pellets of P. ostreatus almost can be formed directly from hyphae and spore aggregation may not be an essential step.