Preliminary Study On The Rhizosphere Chemical Biological Mechanisms Of Radix Pseudostellariae Mediated By Serratia Sp.T241

In our previous studies,a kind of strain was isolated and identified from the rhizosphere soil of Radix Pseudostellariae continuous cropping.After the use of the quorum sensing signal molecules detect bacteria CV026 and 16SrRNA identification determined that this strain was Serratia marcescens who had quorum sensing and could release AHLs(Acyl-homoserine lactones)as signaling molecules.Then the strain was found to be able to harm to Radix Pseudostellariae,and once quenched,it would reduce this damage.This study investigated the growth of Serratia sp.T241 with the extract and exudates from roots and phenolic acids.After construction of the engineering bacteria whose signal molecules were degradated,to explore how the engineering bacteria and Serratia sp.T241 act on Radix Pseudostellariae.The research was divided into four parts:Firstly,added the bacteria to the medium and to explore the growth of Radix with Serratia sp.T241,then to analyze how Serratia sp.T241 damage the Radix Pseudostellariae;Secondly,the engineering bacteria was added to the Radix Pseudostellariae to analyze how Radix Pseudostellaria virulenced by Serratia sp.T241.Thirdly,extracted of the Radix Pseudostellariae roots and its roots' exudates,to explore the growth of Serratia sp.T241 with these extracts,then after adding different concentrations of phenolic acids to the culture medium to investigate the growth of Serratia sp.T241 with phenolic acids;Finally,to explore the effects of the volatile substances from Serratia sp.T241 on Radix Pseudostellariae seedlings in tissue culture by used of half-flat method,and to explore the regulatory relationships between the volatile substances and the growth of Radix Pseudostellariae.The results were as follows:1.The effects of Serratia sp.T241 on situation of Radix Pseudostellariae plantlets and potted seedlings.In this section,Serratia sp.T241 was added to the medium,and the results showed that,T241 would reduce the growth of Radix,even cause death.With the increase of the concentration of T241,the negative impact on potted seedlings were more obvious;While the mixied T241 and BT(Bacillus thuringiensis,BT)T241&BT was added to the medium,with the increase of the concentration of BT,Radix Pseudostellariae were healthier,this might be because there was aiiA gene in Bacillus thuringiensis,so that aiiA gene could degrade the signal molecule of T241 and block the Quorum Sensing of T241,and thus Radix Pseudostellariae could grow normally,Finally,after the screening and identification of internal bacteria from Radix Pseudostellaria seedlings from pot experiments,the Serratia sp.T241 and Bacillus thuringiensis were found.Therefore,the reason why Serratia sp.T241 could affect the normal growth of Radix Pseudostellariae might be due to T241's invading into the inside of Radix Pseudostellariae plants,so that caused the virulence.2.The construction of engineered bacteria which over expression the aiiA gene that can degrade the signaling molecules of specific organism,and potted verification.In this section,the engineered bacteria T241/pBud-aiiA was verfied through quorum sensing signal molecules detect bacteria CV026,PCR and restriction enzyme digestion.The results showed that the T241/pBud-aiiA could over express the aiiA gene,so that it could degrade the signaling molecules of Serratia sp.T241.After adding the T241/pBud-aiiA to Radix potted seedlings,when compared to the blank,the Radix potted seedlings with the T241/pBud-aiiA could grow green and normal.This showed that the quorum sensing was a reason for the process of Radix Pseudostellaria virulenced by Serratia sp.T241,and T241 signaling organism could be degradated by T241/pBud-aiiA,these could finally reduce the the process of Radix Pseudostellaria virulenced by Serratia sp.T241.3.The growth of Serratia sp.T241 with the extract and root exudates from Radix Pseudostellaria and seven kinds of phenolic acid.In this section,Serratia sp.T241 was growed with the extracted of the Radix Pseudostellariae roots and its roots' exudates and seven kinds of phenolic acid substances.The results showed that,in certain concentrations,the extract and exudates from Radix Pseudostellaria roots could promote the growth of Serratia sp.T241,especially the exudates from Radix Pseudostellaria roots.And seven kinds of phenolic acid substances could also promote the growth of Serratia sp.T241.After analysing the exudates from Radix Pseudostellaria roots by HPLC fould that the phenolic acids were not accumulate with the growth of Radix Pseudostellaria,it showed that these phenolic acids might have no effects on allelopathy,and this indirectly showed that phenolic acids might have directly associated with the growth of Serratia sp.T241.In summary can be found that,the extract and the exudates from Radix Pseudostellaria roots could promote the growth of Serratia sp.T241,and this might be why Serratia sp.T241 could become the dominant bacteria in the rhizosphere microorganisms,thus to damage the growth of Radix Pseudostellaria.4.The growth of Radix Pseudostellariae seedlings with the volatile organic compounds from Serratia sp.T241.In this section,by using the two point plate method,the Serratia sp.T241 was found that could release volatile organic compounds certainly,and these substances could make seedlings withered and yellow,and make the roots grow unhealthy.Thus,the virulence effects on Radix Pseudostellariae were showed through the accumulation of volatile organic compounds from T241;and it showed that Serratia sp.T241 had many ways to damage the Radix Pseudostellariae.Thus the virulence effects on Radix Pseudostellariae could be expressed by the accumulation of volatile organic compounds from T241.So the volatile organic compounds might be relevant to the quorum sensing to some extent.