| The fungus Rhizopus arrhizus,synonymous with R.oryzae,is widely distributed in the natural environment and has long been domesticated.So it is necessary to study their physiological indicators,such as saccharifying capacity,temperature adaptability,carbon assimilation and fatty acid composition.The R.arrihizus strains play a role as a producer of glucose in white spirit fermentation.The saccharifying capacity of R.arrihizus were detected and resulted in the curve of glucose concentration.Based on the regression analysis,two strains(R-237 and R-155)were screened out by comparing saccharifying velocity and maximum concentration of glucose.The growth velocity of 69 strains were determined at different temperatures(9,16,23,30,37,40,43,46,49 and 52℃)to research the changes of gowth and death temperature.According to the regression analysis by Excel and SPSS,regression equation of each strain has been calculated.Then the optimum temperature of maximum speed and two critical temperatures were obtained.41.1～44.4℃ and 2.4～10.4℃ are the maximum and minimum growth temperatures of R.arrihizus strains,respectively.And the optimum growth temperatures are 30.0～34.4℃.The theoretical maximum velocity is 3.49～6.01 cm/d.On the basis of the obtained data,three strains(CBS 258.28,R-212,R-165)and other three strains(R-195,R-420,R-248)represent the most sensitive and insensitive strains to temperature change among all strains,respectively.Two strains(R-027,R-487)and other three isolates(R-540,R-248,IFO 4726)have the maximum(52℃)and minimum(40℃)deadly temperatures.These strains are excellent materials for studying temperature adaptability and relative genes in R.arrihizus.A total of 69 R.arrihizus strains were cultivated in seven kinds of media to research the influences.Their growth velocities have been recorded.According to analysis using SPSS,the growth velocities of 69 strains express statistically significant difference.Concretely speaking,strains cultured in CK and dextrin media have significantly different velocities.In addition,strain R-156 displays prestissimo in all cultivation modes,but IFO 4735 grows slowest.Growth velocity of R-198 has been effected slightly by carbon source shift.CBS 279.38 has been greatly affected when cultivated by different carbon sources.Almost 95%of fatty acids in R.arrhizus strains consist of oleic acid,linoleic acid,linolenic acid,octadecanoic acid and cetylic acid.But different R.arrihizus strains have different proportions of five kinds of fatty acids.R-237 has the highest content of octadecanoic acid while R-226 has the lowest content.IFO 4730 has the highest content of linolenic acid but R-437 has the lowest one.R-437 has the highest content of oleic acid,however,IFO 4730 has the lowest content.R-028 has the highest content of linoleic acid but R-437 has the lowest content.R-027 has the highest content of cetylic acid while content of CBS 257.28 is the lowest.The proportion of oleic acid of R-437 is 58.107%,which indicates the strain has potential for oleic production.From four physiological characteristics mentioned above,we found that different R.arrhizus strains have different sensitivities to temperature and carbon source changes,and both sensitivities are inconsistent.Among the strains which have higher maximum glucose concentration(>40.00 mg/mL),it is possible for slower-growing strains to accumulate more glucose in fermentation broth.Cultivated at lower temperatures,the faster growth velocity of R.arrhizus strains change,the higher proportions of polyunsaturated fatty acids have and the lower saturated ones as well.So it shows that lower temperatures facilitate the accumulation of metabolites such as glucose and polyunsaturated fatty acids. |
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