Previously, cellulase and xylanase producing microorganism, Bacillus subtilis NC1, was isolated from soil. Based on the 16S rRNA gene sequence and API 50 CHL test the strain was identified as Bacillus subtilis, and named as B. subtilis NC1. We cloned and sequenced the genes for cellulase and xylanase. Plus, the deduced amino acid sequences from the genes of cellulase and xylanase were determined and were also identified as glycosyl hydrolases family (GH) 5 and 30, respectively. In this study to optimize the medium parameters for cellulase production by B. subtilis NC1 the RSM (response surface methodology) based on CCD (central composite design) model was performed. Three factors, tryptone, yeast extract, and NaCl, for N or C source were investigated. The cellulase activity was measured with a carboxylmethyl cellulose (CMC) plate and the 3,5-dinitrosalicylic acid (DNS) methods. The coefficient of determination (R 2 ) for the model was 0.960, and the probability value (p=0.0001) of the regression model was highly significant. Based on the RSM, the optimum conditions for cellulase production by B. subtilis NC1 were predicted to be tryptone of 2.5%, yeast extract of 0.5%, and NaCl of 1.0%. Through the model verification, cellulase activity of Bacillus subtilis NC1 increased from 0.5 to 0.62 U/ml (24%) compared to the original medium.
The aim of this study was to investigate the optimal conditions for increasing the growth yield of Bacillus subtilis SRCM102046, a strain possessing potential biopreservative properties. B. subtilis SRCM102046 showed remarkable antibacterial activity against a wide range of bacterial foodborne pathogens that cause serious food spoilage, as well as high antioxidant capacity. Response-surface methodology (RSM) was used to optimize medium composition to enhance B. subtilis SRCM102046 biomass. The effects of 14 different components on biomass production were investigated and three significant positive factors, molasses, sucrose, and peptone, were selected as the main factors for improving biomass based on a Plackett-Burman design (PBD). Next, we optimized the concentrations of these three factors using a central composite design. The predicted optimized concentrations were 7 g/L molasses, 7 g/L sucrose, and 2 g/L peptone. The coefficient of determination (R 2 , 0.9755) for the model and probability value showed that our model was highly significant. Finally, an overall approximate 9-fold increase in dry cell weight yield (22.03 g/L) was achieved using the optimized medium compared with the non-optimized medium (2.47 g/L). Furthermore, we confirmed that the antibacterial activity and antioxidant activity also increased by 140% and 100.41%, respectively. These research is expected to be useful data for the production of food preservatives by establishing optimal conditions for increasing the growth yield of microorganisms possessing excellent antimicrobial activity.
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