Lactobacillus plantarum RI 11 was reported recently to be a potential lignocellulosic biomass degrader since it has the capability of producing versatile extracellular cellulolytic and hemicellulolytic enzymes. Thus, this study was conducted to evaluate further the effects of various renewable natural polymers on the growth and production of extracellular cellulolytic and hemicellulolytic enzymes by this novel isolate. Basal medium supplemented with molasses and yeast extract produced the highest cell biomass (log 10.51 CFU/mL) and extracellular endoglucanase (11.70 µg/min/mg), exoglucanase (9.99 µg/min/mg), β-glucosidase (10.43 nmol/min/mg), and mannanase (8.03 µg/min/mg), respectively. Subsequently, a statistical optimization approach was employed for the enhancement of cell biomass, and cellulolytic and hemicellulolytic enzyme productions. Basal medium that supplemented with glucose, molasses and soybean pulp (F5 medium) or with rice straw, yeast extract and soybean pulp (F6 medium) produced the highest cell population of log 11.76 CFU/mL, respectively. However, formulated F12 medium supplemented with glucose, molasses and palm kernel cake enhanced extracellular endoglucanase (4 folds), exoglucanase (2.6 folds) and mannanase (2.6 folds) specific activities significantly, indicating that the F12 medium could induce the highest production of extracellular cellulolytic and hemicellulolytic enzymes concomitantly. In conclusion, L. plantarum RI 11 is a promising and versatile bio-transformation agent for lignocellulolytic biomass.
The gene encoding a cellobiohydrolase 7B (CBH7B) of the thermophilic fungus Thielavia terrestris was identified, subcloned, and expressed in Pichia pastoris. CBH7B encoded 455 amino acid residues with a molecular mass of 51.8 kDa. Domain analysis indicated that CBH7B contains a family 7 glycosyl hydrolase catalytic core but lacks a carbohydrate-binding module. Purified CBH7B exhibited optimum catalytic activity at pH 5.0 and 55 °C with 4-methylumbelliferryl-cellobioside as the substrate and retained 85% of its activity following 24 H incubation at 50 °C. Despite the lack of activity toward microcrystalline substrates, this enzyme worked synergistically with the commercial enzyme cocktail Cellic(®) CTec2 to enhance saccharification by 39% when added to a reaction mixture containing 0.25% alkaline pretreated oil palm empty fruit bunch (OPEFB). Attenuated total reflectance Fourier transform infrared spectroscopy suggested a reduction of lignin and crystalline cellulose in OPEFB samples supplemented with CBH7B. Scanning electron microscopy revealed greater destruction extent of OPEFB strands in samples supplemented with CBH7B as compared with the nonsupplemented control. Therefore, CBH7B has the potential to complement commercial enzymes in hydrolyzing lignocellulosic biomass.