Screening, breeding and metabolic modulating of a strain producing succinic acid with corn straw hydrolyte

Purpose In this paper, the high yield mutant strain was expected to be obtained for the industrial bioconversion of corn straw hydrolyte to succinic acid. Methods API biochemical reactions and 16S r RNA sequence analysis were carried out for identification, and then the strain's metabolic pathway and its relevant enzymes were discussed for the metabolic flux analysis (MFA). The X-ray of synchronous radiation and site-directed mutagenesis were imported for decreasing those byproducts, and the metabolic technics was also modulated. Results Identification showed that the succinic-acid-producing strain S.JST belonged to Actinobacillus succinogenes species. Metabolic pathway analysis indicated that this strain had the character of utilizing glucose and xylose simultaneously, which was a great advantage considering the fact that most crop straw hydrolyte included glucose and xylose. Metabolic flux analysis showed that acetic acid and alcohol competed with the flux of succinic acid, and the analysis of [H] reducing power balance investigated that the [H] electronic donor produced in the cell was not enough for the metabolism of succinic acid. Then X-ray mutagenesis showed that the flux of byproduct acetic acid was decreased to 0.666 from 1.233 mmol/g DW h and that two mutated sites were found in pta (gene of phosphotransacetylase) from mutant strain M.JSTP, but less succinic acid was produced due to the worse lacking in the supply of [H] reducing power. The site-directed mutagenesis showed that the flux of byproduct alcohol was successfully decreased to 0.029 from 1.303 mmol/g DW h. Then, surrounding the flux ratio of HMP to EMP, the metabolic technics was modulated with the addition of citrate in order to improve the balance of [H] reducing power, thus the succinic acid flux of the mutant M.JSTA was increased to 3.163 from 2.480 mmol/g DW h comparing with the parent strain S.JST. Conclusions The mutant strain obtained in this paper deserves to be scaled-up.