Cupriavidus Necator Ferment To Produce PHA With Poplar Fiber As Substrate

Polyhydroxyalkanoates(PHA)are a class of linear polyesters composed of 3-hydroxy fatty acids accumulated in the body microorganism of when its growth conditions are unbalanced.PHA have good biodegradability and excellent performance and it is also a substitute for petroleum-based materials for industrial,medical,and other fields.As a potentially inexpensive renewable raw material,cellulosic biomass can be effectively developed and utilized to synthesize PHA.It can not only efficiently utilize waste cellulosic biomass,but also reduce the production cost of biodegradable plastics.This study was based on poplar lignocellulosic as raw material,after obtaining reducing sugar by dilute acid hydrolysis,Cupriavidus necator was used to fermentation to produce PHA.In this study,the fermentation conditions of one-step and two-step methods,the treatment of different detoxification methods,and the fermentation optimization of hydrolysate as a single carbon source were explored.In addition,molasses was added to the fermentation process to explore the effect of mixed carbon sources on the production of PHA,furthermore to improve the final concentration of PHA.The effects of different stimulants on the production of PHA were also determined.The main results are as follows:In order to improve the saccharification utilization rate of poplar lignocellulosic,reducing sugar was prepared by acid treatment.And the single factor experiments were conducted on the concentration of sulfuric acid,the hydrolysis time and the ratio of solid to liquid,which the Box-Behnken center combination test was designed based on the single factor experimental results,With the reducing sugar content as the index value,the response surface methodology was used to determine the optimal process parameters for degradation.Results show as follows:The optimal conditions to product reducing sugar in the acid pretreatment process were liquid to material ratios of 10.03,acid concentration of 2.03%,hydrolysis time of 103 min,and the average content of reducing sugar was 19.31%.In the experiment of producing PHA by poplar lignocellulosic hydrolysate as a single carbon source,the results show that the two-step fermentation process produces more PHA than one-step fermentation process.Different treatment methods also affect the utilization of the strain to poplar hydrolysate.The effect of using sodium hydroxide to over neutralize first and then using activated carbon to detoxify poplar hydrolysate is the best and the PHA yield is much higher.The optimum parameters obtained by optimizing fermentation conditions are as follows:The nitrogen source was 1 g/L ammonium sulfate,the temperature was 28 °C,the initial pH value was 7,and the fermentation time was 48 h.Under this condition,the yield of PHA was 0.19 g/L.The conditions of PHA production by mixed carbon source fermentation were optimized by single factor and response surface method.The results showed that the molasses added amount was 27.4 g/L,the nitrogen source concentration was 1.88 g/L,and the temperature was 29.9?.Under these conditions,the average PHA value was 0.83 g/L.PHA experiments on the fermentation of mixed carbon sources by acid irritant and hyperosmotic stimuli showed that acetic acid below 1 g/L could increase the yield of PHA,but when the concentration of acetic acid reached 1.5 g/L,acetic acid has an inhibitory effect on the strain,which makes the strain no longer continue to grow.The addition of sodium chloride inhibited the production of PHA.The higher the concentration of sodium chloride,the worse the growth and accumulation of PHA.The strain stopped growing when the concentration of sodium chloride was 10 g/L,and the accumulation of PHA was no longer carried out.