| Polyhydroxyalkanoates(PHA)are usually stored in microorganisms as carbon sources and energy.They have similar properties to traditional petroleum-based plastics and are regarded as environmentally friendly materials because of their good degradation ability in natural environment.PHA compounds are widely used in medical field because of their excellent biocompatibility.They have piezoelectric and conductive properties,and are widely used in the field of materials because they are made of different monomers.They are also used in agricultural production to encapsulate pesticides due to their biodegradability.With the heightening of research on PHA,increasing the synthesis of PHA and reducing PHA production cost have become the hotspot in the field of PHA research.When halophilic bacteria are used as the starting strain,the high-yield characteristics of pure bacteria fermentation can be brought into play,and the tolerance of halophilic bacteria to high salinity and alkali environment can reduce the tedious sterilization links,thus developing a low-cost platform for open culture.Based on the halophilic bacteria preserved in the laboratory,a strain with the largest PHA synthesis was 41%selected and identified and fermentation conditions were optimized.The properties of PHA materials synthesized by the strain were analyzed by FT-IR,DSC,XRD and degradation experiments.Halomonas sp.Z-1 was Gram-negative,malonate-positive,and Simon's citrate-positive,and could not reduce nitrate,but produced H2S and liquefy gelatin.The strain was also analyzed by 16S rDNA sequence,was identified as Halomonas sp.and named Z-1.The login number was MH428215.The effects of nutrition and culture conditions on the production of PHA by Halomonas sp.Z-1 fermentation and the growth law were studied.Z-1 can synthesize PHA compounds from glucose,sucrose,lactose,maltose,mannose,soluble starch and other carbon sources;it is sensitive to chloramphenicol and rifampicin,and resistant to streptomycin,gentamicin,ampicillin,and kanamycin.Through shake flask experiment,it was found that the optimum conditions for high-yield PHA production by Halomonas sp.Z-1 were 37?,pH 9.0,160 r/min,liquid volume 90 mL in 500 mL triangular bottle,and 52h cultivation;the maximum synthesis of PHA was 56%.Infrared spectroscopy was used to analyze the PHB standard sample and the polymer synthesized by Halomonas sp.Z-1.The results showed that the two spectra were similar.The characteristic absorption peaks of PHB appeared at 1726,2980,2934,and 2876 cm-1.The product synthesized by strain Z-1 using glucose,nonic acid,and decanoic acid as carbon sources was PHB.By analyzing the temperature rise curve of DSC,it can be seen that the Tm value of the product is 61.40? with glucose as carbon source,62.30? with hexanoic acid as carbon source,53.40? with pelargonic acid as carbon source,70.40? with decanoic acid as carbon source,77.40? with undecanoic acid as carbon source,therefore,the selection of substrates affects the composition and properties of the product.Glucose,butyric acid and valeric acid were synthesized as carbon sources respectively.Within two months,the weight loss rate was about 66%,indicatung that the PHA products of Halomonas sp.Z-1 had excellent degradability under natural conditions.Above all,Hatowonas sp.Z-1 has high advantages as a platform for the synthesis of PHA compounds.Hence,this lays the foundation for further research on its utilization of cheap substrates under open conditions,and also provides the necessary theoretical basis for future large-scale production and application. |
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