| Butyric acid is an important and widely used raw material especially for that it can aslo be basic material for production of biofuel-butanol.The main method for production of butyric acid is chemical synthesis which is primarily based on nonrenewable fossil resources.Clearly,it is unsustainable and will aggravate the serious environment problems meanwhile.Butyric acid production by microbial fermentation from crop straw and other lignocellulosic resources can not only achieve the target for reasonable utilization of straw resource and avoid environmental problems caused by its improper treatment,but also can be a reliable raw material supply for for chemical industry.In order to solve the problems such as the low quality? high price of raw materials and excessive byproducts of current fermentation technology for butyric acid production,the study was carried out from the screening of lignocellulose-degrading bacteria ? construction of combined flora and other aspects to obtain butyric acid producing bacteria resource and explore the feasibility of buryric acid production from rice straw by combined flora.Besides,the study can also prepare the bacteria sources and develop the fermentation technology for sustainable production of butyric acid.Two butyric acid producing bacterium were isolated from undefined mixed culture which was enriched and cultured from rice straw.Two strains all belong to Clostridium genus by observation of morphological?physiological-biochemical and identification of genetic characteristics and thus was named Clostridium cadaveris C4 with cllulose-degrading ability and C.butyricum B20 which can ferment cellobiose.SEM(scanning electron microscope,SEM)obversation showed that the cell of strain C4,G+,was spindle shaped with length of 2~4 ?m and maximum diameter of 0.4 ?m;Srain B20,G+,was rod-shaped with a diameter of about 0.8 ?m and a length of 4~7 ?m.Two strains all showed good ability for butyric acid production.Besides the above two strains Clostridium cadaveris C4 and C.butyricum B20,xylan-degrading bacteria named C.butyricum X3 which was already isolated and identified as pure culture was also used for construction of microflora and testing the capability of butyric acid production by fermentation of rice straw.The result showed that co-fermentation of three strains can fully utilize synergistic metabolism among mixed culture and significantly improved the degradation of rice straw and yield of butyric acid.On condition of 1:1:1(v/v)mixing plan,0.93 and 1.53 g/L of butyric acid and total VFAs(volitial fatty acids,VFAs)accompanied with rice straw degradation amount of 3.10 g/L were obtained by fermentation of combined microflora with three strains.Meanwhile,the proportation of butyric acid in total VFAs can reached 61.16%.Also,the ratio butyric acid prodution rate was 0.18 g/(gDCW?h)during logarithmic period which increased by 50%,200% and 63.64% compared with C4?B20 and X3 respectively proving that it is excellent bacteria souce for production of butyric acid from rice straw.The obtained optimum matching programme for C.butyricum X3?C.cadaveris C4 and C.butyricum B20 was 1:2:2(v/v),and the optimum fermentation conditions obtained were 35?,initial p H=5,inoculation amount 0.22 g/L,substrate concentration 10 g/L,1 g/L peptone as nitrogen source respectively by optimization study of matching programme and culture conditions. |
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