Study On Screening,Optimization And Application Of Succinic Acid Producing Bacteria

Succinic acid(C₄H₆O₄)is a kind of tetracarboxylic acid with potential application value.It is often used as the starting material for the synthesis of general chemicals and has a broad application prospect in the fields of chemistry,food,medicine,health and agriculture.At present,the production of succinic acid by the traditional chemical method has many defects,such as consuming a lot of non-renewable petroleum raw materials,high production cost and environmental severe pollution.Given the above problems,the production of succinic acid by microbial fermentation using biomass raw materials is not only environmentally friendly,but also can fix CO₂,which has opened up a new way to reduce the emission of greenhouse gas CO₂.It has the advantages of using renewable resources,low cost and environmental protection,and promotes the large-scale utilization of agricultural and forestry wastes,which has important practical significance.In this paper,LW-2,a high-yield succinic acid producing strain,was screened from the rumen contents of cattle.The optimal fermentation time,culture temperature,pH regulator and dosage of LW-2 for succinic acid production were determined with glucose and xylose as carbon sources,respectively.A high-efficiency catalytic system was established to determine the selective conversion of hemicellulose in corncob by single factor experiment.It can guide the selective dissolution and efficient utilization of hemicellulose in biomass.The main results are as follows:(1)LW-2 was isolated from the rumen of cattle.Glucose and xylose were used as carbon sources for preliminary fermentation experiments.The concentration of succinic acid was 4.48 g/L and 5.27 g/L,and the strain was used as the experimental strain in this paper.After the identification of basic physiological and biochemical properties and 16S rDNA sequence analysis,LW-2 was preliminarily identified as Escherichia fergusonii,which is a new type of wild facultative anaerobic succinic acid-producing bacteria with low nutritional requirements.(2)The optimal fermentation conditions of succinic acid production by LW-2 were determined by a single factor experiment.The optimal fermentation time for succinic acid production by glucose was 24 h,temperature 40?,inoculation amount 2.5%,pH regulator MgCO₃,dosage 30 g/L.under this condition,the yield of succinic acid was 6.36 g/L,the yield of succinic acid was 21.2%;the optimal fermentation time for succinic acid production by xylose was 66 h,temperature 37?,inoculation amount 7.5%,pH regulator MgCO₃,dosage 30 g/L.The yield of succinic acid was 7.51g/L,and that of succinic acid was 25.0%.(3)In order to investigate the effect of different catalysts on the selective dissolution of hemicellulose and the preparation of xylose,Fe₂(SO₄)₃-NaCl-H₂O was used to catalyze the hydrothermal pretreatment of corncob.Fe₂(SO₄)₃ can inhibit the conversion of cellulose and lignin,promote the reaction to produce xylose and formic acid,inhibit the reaction to produce acetic acid,and improve the selectivity of hemicellulose to xylose.NaCl can promote the reaction to generate hemicellulose and xylose,and inhibit the conversion of lignin.(4)The single factor experiment was used to determine the optimal reaction time of hemicellulose conversion and xylose yield under the catalysis of Fe₂(SO₄)₃-NaCl-H₂O.The optimal dosage of Fe₂(SO₄)₃ was 1g,NaCl was 1g,and the optimal reaction temperature was 120?140?.Under these conditions,hemicellulose can be selectively converted into xylose with a yield of 106.9wt%(calculated according to the mass of hemicellulose).Cellulose(7.9 wt%)and lignin(21.2 wt%)were not significantly affected.Using hemicellulose hydrolysate as raw material,the succinic acid yield of 15.8% can be obtained by Escherichia fergusonii fermentation.