Process development of succinic acid production from sorghum straw by Actinobacillus succinogenes NP9-aA7

Abstract

The aim of this study emphasized the isolation, screening, identification and optimization of the potential bacteria for succinic acid production. From primary screening, 171 isolates exhibited a clear zone on the screening medium. From qualitative analysis, 165 isolates gave positive by TLC. The potential 58 isolates were selected with quantitative analysis by HPLC for phenotypic characteristic. Fifty-eight isolates were divided into 11 groups. Representative isolate from each group have been identified based on its 16S rRNA sequence analysis. They were closely belonged to genus Enterococcus, Streptococcus. Lactobacillus, Clostridium, Lactococcus., Proteus. and Actinobacillus. Among 11 groups, the isolate NP9-aA7 representative from group X was isolated from the bovine rumen. It gave a high succinic acid of 42.539 g/L with a yield of 0.709 g/g glucose. It was identified to Actinobacillus succinogenes, non-motile, non-spore-forming, gram-negative rod and non-pathogenic. The statistical method combining a one factor at a time method, a Plackett-Burman Design (PBD) and a Box-Behnken Design (BBD) using a Response Surface Methodology (RSM) were developed to optimize succinic acid production by A. succinogenes NP9-aA7. Key medium consisted of 74 g/L of glucose, 30 g/L of yeast extract and 60 g/L of alkaline neutralizer (45 g/L of MgCO₃ and 15 g/L of Mg(OH) ₂) gave a maximum succinic acid to 60.087 g/l with a yield of 0.816 g/g glucose after 36 h of cultivation time. Batch fermentations in a 2 L fermenter, the model was validated with succinic acid of 58.080 g/L after 27 h of cultivation time. Addition of CO₂ partial pressure in the medium had significant improved the production of succinic acid to 72.930 g/l with a yield of 1.393 g/g glucose at the CO₂ partial pressure of 50.66 kPa after 24 h of cultivation time. Using sorghum straw hydrolysate as an alternative carbon source, A. succinogenes NP9-aA7 gave a succinic acid of 19.139 g/L closely to type strain of A. succinogenes DSMZ 22257. It could be suggested that SSH, a renewable material, could be used as an alternative carbon source for succinic acid production by A. succinogenes NP9-aA7.