Isolation,Identification And Degradation Characteristics Of Amygdalin-degrading Bacterial Strain

The replant obstacles of peach trees are common at home and abroad,which is a worldwide problem.A large number of researches proved a correlation between cyanogen glucoside and peach replanted problem.Cyanogen glycosides in soil produce harmful substances such as benzaldehyde and hydrocyanic acid under the action of microorganism,which affect the growth of peach trees.Amygdalin is reported to be one of the major forms of cyanogen glycosides in peach trees.In this study,soil microorganisms which could degrade amygdalin were screened out from the rhizosphere soil of ten year old peach trees at the fruit tree base of Huazhong Agricultural University.To understand the isolated microbes,we firstly performed the microbes identification,as well their growth and degradation characteristics.Using model bioassay receptor plant lettuce,we tested the toxicity of the degradation products of amygdalin,and the change of CN~-concentration during the degradation of amygdalin.Subsequently,the growth conditions of WHA-4 was optimized.Furthermore,the effects of the catabolites of amygdalin on peach seedling growth were explored.The main results are as follows:1.Five strains of amygdalin-degrading bacteria were isolated from peach rhizosphere soil.Combined morphological observation and the analysis of 16Sr RNA gene sequencing,five amygdalin degrading bacteria were preliminarily identified as Stenotrophomonas maltophilia(WHA-1),Citrobacter(WHA-2),Pseudomonas aeruginosa(WHA-3),Arthrobacter nicotinicus(WHA-4),Agrobacterium tumefaciens(WHA-5),respectively.2.The results showed that WHA-4 owned the strongest ability of growth and amygdalin degradation.Compared to the control,the height of lettuce seedlings was decreased significantly at the 72 h degradation products of WHA-1.The height and fresh weight of lettuce seedlings were lowered significantly at 24 h degradation products of WHA-4,and the height of lettuce seedlings at 36 h was also significantly reduced.The germination index,germination speed index and height of lettuce seedlings at 24 h degradation products of WHA-5 were significantly lowered.3.In the process of degradation of amygdalin,WHA-4 produced the most CN~-in 24h,then the concentration of CN~-gradually decreased,and was completely consumed at last.When adding 100 mg/L peptone into the culture medium,the maximum concentration value of CN~-was decreased,but the consumption rate of CN~-increased at the later stage.WHA-4 showed great difference in growth and degradation ability under various external conditions.The results showed that The optimum growth and degradation ability of WHA-4 at 25?and 400 mg/L for amygdalin is the best.The optimum pH for WHA-4 growth is 5-5.5,and the optimum pH for the degradation of amygdalin is 5-6.The addition of glucose,glucose+ammonium sulfate,peptone or yeast to the medium could promote the growth and degradation capacity of WHA-4,while the addition of ammonium sulfate could inhibit the growth and degradation.4.The 24 h degradation products of WHA-4 inhibited the growth of peach seedlings.Compared with the control,the plant height,dry diameter,stem dry weight and root dry weight were significantly reduced.