Novel Strain of Paenibacillus phyllosphaerae CS-148 for the Direct Hydrolysis of Raw Starch into Glucose: Isolation and Fermentation Optimization

Abstract

The conventional process for converting starch to glucose is energy-intensive. To lower the cost of this process, a novel strain of Paenibacillus phyllosphaerae CS-148 was isolated and identified, which could directly hydrolyze raw starch into glucose and accumulate glucose in the fermentation broth. The effects of different organic and inorganic nitrogen sources, the culture temperature, the initial pH, and the agitation speed on the yield of glucose were optimized through the one-factor-at-a-time method. Nine factors were screened by Plackett–Burman design, and three factors (raw corncob starch, yeast extract and (NH₄)₂SO₄) had significant effects on glucose yield. Three significant factors were further optimized using Box-Behnken design. Under the optimized fermentation conditions (raw corncob starch 40.4 g/L, yeast extract 4.27 g/L, (NH₄)₂SO₄ 4.39 g/L, KH₂PO₄ 2 g/L, MgSO_{4`</sub>7H<sub>2</sub>O 2 g/L, FeSO<sub>4`}7H₂O 0.02 g/L, NaCl 2 g/L, KCl 0.5 g/L, inoculums volume 4%, temperature 35 °C, agitation rate 150 rpm, and initial pH 7.0), the maximum glucose yield reached 17.32 ± 0.46 g/L, which is 1.33-fold compared to that by initial fermentation conditions. The maximum conversion rate and glucose productivity were 0.43 ± 0.01 g glucose/g raw corn starch and 0.22 ± 0.01 g/(L·h), respectively. These results implied that P. phyllosphaerae CS-148 could be used in the food industry or fermentation industry at a low cost.