The Colonization Of Agrobacterium Species Induced By Different Organic Acids And Its Mechanism Of Cd Molization

In the early of the experiment,a bacterial strain T29 with potassium-solubilizing ability was isolated from farmland soils in the suburb of Guangzhou.It was identified as Agrobacterium species based on the morphological,physiological and biochemical characteristics and 16S rDNA sequence analysis.Shake-flask experiments were used to assess the ability of T29 to mobilize CdCO₃.The molecular mechanism to mobilize Cd of T29 in the medium with and without K⁺was studied by metabolomics.The metabolic response changes of T29 affected by K⁺was revealed.Meanwhile,the whole genome of T29 was measured through high-throughput sequencing,which laid the foundation for the later application of genomics to study the Cd mobilization mechanism.Then,the colonization of T29,induced by various organic acids and amino acids,and its mobilization of Cd in the soil was investigated via chemotaxis,swarming,in vitro and pot experiments,so as to determine the signal molecule of T29.The results were crucial to the development of phyto-microremediation technology for cadmium-contaminated farmland and the safety of agricultural products.The main results were as follows:?1?In the shake-flask experiment,the mobolized P and Cd contents in the culture medium were significantly higher than those of no inoculation groups?p<0.05?.With the increase of K⁺content in the medium,mobilized P and Cd content of T29 also increased,and in the 100 mg·L^-1K⁺medium,P and Cd contents were 65.6 and 43.0 mg·L^-1,respectively.Meanwhile,the extracellular metabolites contents secreted by T29 in the 100 mg·L^-11 K⁺medium were significantly different from no K⁺groups.Among them,the content of 3-hydroxybutyric acid,valine,succinic acid,glyceric acid,2-hexenoic acid,fumaric acid,serine,3,4-dimethylbenzoic acid,tartaric acid and azelaic acid significantly increased?p<0.05?.The pivotal metabolic pathway,such as butanoate metabolism,arginine and proline metabolism,and citrate cycle all had obvious changes.The studies showed that K⁺could promote T29 to secrete more organic acids and amino acids,and strengthen its ability to mobilize the insoluble Cd and P.K⁺could had a significant effect on the metabolic activity of T29.?2?In the chemotaxis and swarming experiments,the numbers of colonies and the diameter of T29 grown in culture medium with gluconic acid were 3.65×10⁶ cfu·mL^-11 and 2.18 cm,respectively.In the vitro experiments,the colony number on the root surface were 2.98*10⁶ cfu·g^-1 fresh root weight and was 29.1%higher than that of the control groups.In the pot experiments,compared with control groups,available phosphorus and potassium in the rhizosphere soil increased by 37.5%and 52.8%,respectively.The phosphorus and potassium concentrations in root did no significantly change?p>0.05?.The Cd content was 2.09 mg·kg^-1,increasing 122.3%compared with no inoculation groups.Meanwhile,the content of Cd,P and K in shoots were 1.73mg·kg^-1,6.36 and 21.32 g·kg^-1,increasing by 78.4%,49.3%and 56.4%compared with no inoculation groups.The dry weight of root and shoots were 0.49 and 3.96 g,increasing by 24.2%and 50.2%,respectively.The height of Chinese flowering cabbages was 37.9 cm,which was 1.48times of no inoculation groups.These results suggested various organic acids and amino acids influenced T29 colonization differently.Gluconic acid preferably strengthened the colonization process of T29 in the rhizosphere of Chinese flowering cabbages,thereby mobilizing more soil P,K and Cd.?3?Through sequencing the complete genome of T29,Raw Data was 760 Mb,Total Reads was 5,070,632,Filtered Clean Data was 392 Mb,and Filtered Reads was 4,825,213,which took up95.16%of the total sequence.These results showed this sequence had high accuracy.Filtered Reads were assembled and had 5486 gene sequences,whose total length was 4,988,409 bp and GC content was 60.59%.The functional annotation of gene sequences was performed in 11 databases.The amounts of annotated genes on GO,IPR,KEGG,COG,NR,SwissProt,TrEMBL,CAZy,ARDB,PHI,and T3SS were 3426,4606,3299,4353,5210,2143,5164,92,21,109 and 477,but the genes related to carbohydrates and amino acid metabolism were 346 and 347,respectively.