| Poly-?-hydroxybutyrate(PHB)is one of the most common biodegradable plastic in the family of PHA,is also one of the most extensive and most thorough study of the kind of material.PHB is made of the ?-helix secondary structure which formed with a lot of Type D monomer HB.It's crystallization of highly three-dimensional specificity,and the crystallinity is about 55%~80%.The molecular structure and physical properties of PHB molding purification such as melting point,crystallinity,tensile strength are similar to PP.Under natural conditions,PHB can be degraded thoroughly to CO2 and H2 O by many microorganisms in the environment.The good biodegradability can help to alleviate the "white pollution" problem.Therefore,PHB is a kind of environmental friendly plastics.PHB is often used as fixation materials such as surgical suture,tooth filling materials,heart stents,and elbow nail because it has a good biocompatibility and no strong immune response for human body.It can also be used as the replacement of vascular and bone plate surgery.In addition,PHB material is piezoelectric,so it can also be made into industrial voltage products.Chromohalobacter sp.ST307 is a kind of moderately halophilic bacteria.Because of its relatively high salt tolerance,the cost can be reduced from the perspective of sterilization in industrial production.There are a lot of studies in our laboratory.At present,the complete sequence of the gene has been sequenced,and the choline dehydrogenase gene and the betaine synthetase gene have been cloned and analyzed.The expe rimental results showed that the PHB could be produced and accumulated by the black staining and the ultraviolet wavelength identification of Chromohalobacter sp.ST307 in Sultan.The A235 showed that the PHB yield of SH307 without optimization was 1.48 g / L and the concentration of PHB was 29.48% of the dry weight of the cells.The optimum medium for the production of Chromohalobacter sp.ST307 was determined by six single factor experiments: salt concentration,carbon source species,nitrogen source type,C / N ratio,carbon and nitrogen concentration and culture time.Each 100 m L of PHB medium contains 5.25 g of sucrose,1.5 g of tryptone,0.03 g of magnesium sulfate heptahydrate,0.01 g of calcium chloride,0.003 g of potassium dihydrogen phosphate,0.01 g of dipotassium hydrogen phosphate trihydrate,0.002 g of ferric chloride and 6 g of sodium chloride.The different temperature,speed,p H,liquid volume are set in CCD response surface experiment.The temperature levels are 27,31 and 35 ° C;the speed levels are120,160 and 200 r / min;p H levels are 6.6,7.0 and 7.4;the liquid level are 40,80 and 120 m L.Finally we get the optimal scheme,when temperature was 20.09 ?,shaking speed was 200 r / min,p H was 6.0,and liquid content was 40.02 m L,the OD235 of PHB could reach 1.59,and PHB yield was 6.78 g / L.It increased four times compared with the PHB yield 1.48 g / L of SH307 without optimization.The function gene phb A(ST307GL000184),phb B(ST307GL000185),and phb C(ST307GL000186)have been identified in the ST307 whole-genome sequence of the ST307.The sequence of genes antimeanings and the sequence of proteins are shown in figure 1-3.The three PHB functional genes of Chromohalobacter sp.ST307 are linked,and it has been preliminarily inferred that they are located at the same operation.The transmembrane region,two stage structure and domain of the three genes encoding proteins were predic ted,which laid a theoretical foundation for further research on the structure of the coding protein. |
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