| Polyhydroxyalkanoate(PHA)has a wide range of physical properties and can replace a variety of chemical raw materials,so it has been applied in various fields.However,the high production cost of PHA,which is 4-5 times higher than that of petroleum-based plastics,seriously affects the broad application of PHA:therefore,there is a need to device a means to increase PHA production at a low cost.According to the characteristics of halophilic bacteria,the non-sterilization continuous fermentation model can be developed,which is of great significance for reducing the production cost of PHA and promoting the sustainable development of the PHA industry.A halophilic bacterial strain with high PHA production was screened from saline-alkali soil in the Daqing area of Heilongjiang Province.The accumulation of PHA was determined by Sudan black B staining and Albert heterochromatic granule staining.The strain was identified as Halomonas sp.by morphological observation and molecular biology and named ZY-1.The effects of nutrient culture conditions and fermentation models on PHA synthesis by strain ZY-1 and the growth rule of strain ZY-1 were preliminarily studied.The results showed that the best carbon source was glucose:the best concentration of NH4Cl was 1 g/L:the best concentration of KH2PO4 was 1.5 g/L;the most potent ability of strain ZY-1 to synthesize PHA w as 2.8 g/L at pH 9.Based on this condition,two batch feeding methods were adopted to increase the production of PHA.The first one was to control the concentration of glucose at 20-50 g/L,and the highest PHA obtained was 5.76 g/L,accounting for 48%of the cell dry weight,which was 2.05 times of the production of PHA by shaking flask fermentation.The second strategy of feeding was to increase the concentration of glucose to a high concentration100 g/L with a single pulse.The final PHA yield was 4.9 g/L,accounting for 42%of the cell dry weight,which was 1.75 times the yield of the shake flask fermentation PHA production.Fourier-transform infrared spectroscopy(FTIR)was used to compare three different materials produced from sodium acetate(2C),glucose(6C),and oleic acid(18C)with a PHB standard sample.The results showed that the characteristic absorption peaks of the three materials were identical with that of the PHB standard sample,indicating that the products synthesized by strain ZY-1 using different carbon sources were PHA materials.The physical properties of three kinds of PH A materials were analyzed by X-ray diffraction(XRD).scanning electron microscopy(SEM),and differential scanning calorimetry(DSC).The results showed that the longer the carbon chain of the carbon source,the better the toughness,transparency,and film-forming property of the synthesized PHA.and the worse the crystal liniy.The melting temperatures of the three kinds of PHA were similar,between 160 and 170?.with excellent thermal stability.In order to explore the degradation of PHA.this experiment analyzed the degradation of PHA in different environments.The results showed that the weight loss rate of PHA in soil was greater than that in the PBS buffer solution.In different pH solutions,the weight loss rate of PHA was:pH 12.0>pH 9.0>pH 3.0>pH 7.0.In conclusion,the PHA materials have good biodegradability.In order to develop a low-cost carbon source for PHA synthesis,the accumulation of PHA from rice straw and oleic acid was studied.The results showed that the highest yield of PHA was 0.0805 g/L when fermented in the straw medium for 84 hours,and the synthesized PHA was brown powder.In the straw oleic acid medium,when the volume ratio of straw supernatant to oleic acid was 45:1.the yield of PHA reached 1.57 g/L.PHA was relatively transparent and tough with better biofilm. |
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