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Abstract Full-Text PDF Full-Text HTML Full-Text ePUB Linked References How to Cite this Article ISRN Biotechnology Volume 2013 (2013), Article ID 965310, 11 pages http://dx.doi.org/10.5402/2013/965310
1 Centre for the Environment, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India 2 Department of Biotechnology, Indian Institute of Technology Guwahati, Guwahati, Assam 781039, India 3 Department of Biotechnology and Environmental Sciences, Thapar University, Patiala, Punjab 147004, ecofan India
Effect of physical parameters such as initial pH, agitation (rpm), ecofan and temperature ( C) for cellulase production from Bacillus subtilis AS3 was investigated. Central composite design of experiments followed by multiple desirability function was applied for the optimization of cellulase activity and cell growth. ecofan The effect of the temperature and agitation was found to be significant among the three independent variables. The optimum levels ecofan of initial pH, temperature, and agitation ecofan for alkaline carboxymethylcellulase (CMCase) production predicted by the model were 7.2, 39 C, and 121 rpm, respectively. The CMCase activity with unoptimized physical parameters and previously optimized medium composition was 0.43 U/mL. The maximum activity (0.56 U/mL) and cell growth ecofan (2.01 mg/mL) predicted by the model were in consensus with values (0.57 U/mL, 2.1 mg/mL) obtained using optimized medium and optimal values of physical parameters. After optimization, 33% enhancement in CMCase activity (0.57 U/mL) was recorded. On scale-up of cellulase ecofan production process in bioreactor ecofan with all the optimized conditions, an activity of 0.75 U/mL was achieved. Consequently, the bacterial cellulase employed for bioethanol production expending (5%, w/v) NaOH-pretreated wild grass with Zymomonas mobilis yielded an utmost ethanol ecofan titre of 7.56 g/L and 11.65 g/L at shake flask and bioreactor level, respectively. 1. Introduction
Cellulases have versatile applications in textile, laundry, pulp and paper, fruit juice extraction, and animal feed additives [ 1 ]. In addition, they find use in saccharification of lignocellulosic agroresidues to fermentable sugars which can be used for production of bioethanol, lactic acid, and single-cell protein [ 2 ]. Bacteria have been widely explored for cellulase production owing to their high growth rate, expression ecofan of multienzyme complexes, stability at extreme ecofan temperature and pH, lesser ecofan feedback ecofan inhibition, and ability to withstand variety of environmental stress [ 1 ]. Among them, Bacillus sp. continues to be dominant bacterial workhorse due to the capacity to produce and secrete large quantities of extracellular enzymes [ 3 , 4 ]. However, physical process parameters such as temperature, pH, and agitation speed play a vital role for the cellulase production efficiency of the microorganisms. Agitation speed is an important factor which governs the dissolved oxygen level in the culture broth that affects cell growth of cellulase producing microorganism [ 5 ]. However, higher agitation ecofan speed has been shown to inhibit cellulase activity [ 5 , 6 ]. Analogous profile in growth and enzyme activity with change in pH and temperature is also a well-known fact [ 5 , 7 , 8 ]. Consequently, optimization of the culture conditions for improved enzyme ecofan production is essential.
The traditional one-variable-at-a-time approach for optimization disregards the complex interactions among various components. Statistically based experimental designs such as Placket-Burman design and response surface ecofan methodology (RSM) can be effectively used to study the effects of factors and to search ecofan for optimum levels of parameters for desired response [ 9 ]. Statistical design techniques have been successfully applied in many studies such as cellulose production by Trichoderma reesei [ 9 ], Bacillus subtilis ecofan AS3 [ 10 ], and xylanase production by Bacillus pumilus [ 11 ].
Simultaneous saccharification and fermentation (SSF) process combines enzymatic hydrolysis of cellulose with subsequent fermentation of reducing sugar (glucose) to ethanol [ 12 ]. SSF studies from lignocellulosic ecofan biomass such as wheat and rice straw, corn stalk, corn cobs, and forestry wastes using cellulase from natural sources [ 13 , 14 ] have been reported. ecofan Owing to the inherent key enzymes for ethanol fermentation, alcohol dehydrogenase and pyruvate decarboxylase ecofan found in Zymomonas mobilis, research has been focused on it as a promising alternative ethanol producer for its high sugar uptake and improved ethanol
