Sonoporation of Ganoderma lucidum mycelium for high biomass and exopolysaccharide productivity in submerged culture

Abstract

Ganoderma lucidum, known as Lingzhi in China and Reishi in Japan, is a famous medicinal mushroom that is commonly produced by solid-state fermentation. Recently, submerged culture has been considered as a promising alternative for production of G. lucidum. Herein, to provide a theoretical base for preparation of a homogenous inoculum for G. lucidum submerged culture we investigated the effect of sonoporation on G. lucidum mycelium. Submerged culture was also evaluated using the sonoporated mycelium. Microscopic investigation indicated that the mycelial pellets (0.55 g, dry weight) contained in 60 mL solution were almost completely disappeared within 20 s by sonoporation (20 kHz and 125 w). The homogenate obtained after sonoporation had a 3.75×106 cfu/mL cell concentration. The sonoporation caused rapid leakage of intracellular protein that increased linearly with time. The metabolic activity of the cells decreased rapidly after sonoporation. Sonoporation also negatively affected laccase activity. When the homogenate was used at 4.76% (v/v) inoculum level, the cultures produced biomass and exopolysaccharide of 15.75 and 0.54 g/L, respectively; these values were 129.26 and 45.95% higher than that of the control culture using a pellet-type inoculum without sonoporation. Optimal inoculum size was 5.88-6.97% (v/v). We conclude that sonoporation is an effective method for homogenization of G. lucidum mycelium, and sonoporated mycelium can improve productivity significantly in G. lucidum submerged culture and requires lower levels of starting inoculum.