Solid state fermentation (SSF)-derived cellulase for saccharification of the green seaweed Ulva for bioethanol production

Abstract

Cellulase produced from the marine fungus Cladosporium sphaerospermum through solid state fermentation (SSF) was investigated for its saccharification potential of seaweed biomass using the common green seaweed Ulva fasciata. The seaweed substrate, containing inoculated fungus with 60% moisture content, cultured at 25°C and pH4 for four days, showed optimum enzyme production. The enzyme, assayed for carboxymethyl cellulase and filter paper assay, showed an activity of 10.20±0.40U/g and 9.60±0.64U/g on a dry weight basis, respectively. Further, ionic liquid tolerance of the enzyme was studied in the presence of 1-ethyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium trifluoromethanesulfonate and 1-butyl-1-methylpyrrolidinium trifluromethanesulfonate. At 10% v/v concentration, the enzyme retained 72.17 to 85.04% activity in all the ionic liquids. The pre-incubation of enzyme in the same ionic liquids for 24h, the activity got slightly enhanced and ranged between 73.80 and 93.70%. The hydrolysis of U. fasciata feedstock with enzyme (10U/g) for 24h at 40°C and pH4 gave maximum yield of sugar 112±10mg/g dry weight. On fermentation, an ethanol yield of 0.47g/g reducing sugar was obtained, corresponding to 93.81% conversion efficiency. These findings indicate that cellulase produced from a marine fungus can be employed for saccharification of cellulosic feedstock for the production of renewable biofuels from marine macroalgal feedstock. Since bioethanol yields obtained compare very favorably with those from land crops, the strategy employed in this study warrants further exploration.