Utilization of rice straw for laccase production by Streptomyces psammoticus in solid–state fermentation

Abstract

Laccase production from a novel actinobacterial strain, Streptomyces psammoticus. MTCC 7334 was optimized in solid-state fermentation. The process parameters were initially optimized by the conventional "one factor at a time" approach, and the optimal levels of the factors that has considerable influence on enzyme production were identified by response surface methodology. Rice straw was identified as a suitable substrate for laccase production (17.3 U/g) followed by coffee pulp (15.8 U/g). Other optimized conditions were particle size. 500-1000 Mum (21.2U/g); initial moisture content, 65% (26.8 U/g); pH of moistening solution, 8.0 (26.9 U/g); incubation temperature, 32°C (27.6 U/g) and inoculum size, 1.5 x 10 rise to 7 CFU (33.8 U/g). Yeast extract served as the best nitrogen source (34.5 U/g). No enhancement in enzyme yield was observed with carbon supplementation. The level of yeast extract inoculum size and copper sulphate were optimized statistically. Statistical optimization performed using a central composite design resulted in threefold increase in laccase activity (55.4 U/g) as compared to the unoptimized medium (17.3 U/g). The upgrading of fermented rice straw for fodder enhancement is also discussed briefly.