Isolation And Characterization Of Novel Bacteria Containing Acc Deaminase And Inoculation Effects On Maize Seedling Growth And Betaine Metabolism Under Drought Stress

Soil-microbe-plant interactions are known to be intricate and they can greatly influence the crop vigor and yield. Plant growth promoting bacteria living in plant rhizosphere containing ACC deaminase can markedly influence plant metabolic processes under stress conditions.In the present study, we isolated 300 bacterial strains from the rhizosphere of maize grown in drought-hit soil including four different locations of the Loess Plateau, China. Of all isolated strains, four with ACC deaminase activity(ranging from 28.88 to 155.12 nmol α-ketobutyrate mg-1 h-1) were further studied by determining their biological characters and sequencing the 16 S rRNA gene. All four strains showed positive performance in terms of arabinose, citrate utilization, urease, indol, glucose and melibiose. In connection with the results of biochemical characters and phylogenetic analysis, these strains commonly belong to three different genera: Klebsiella, Pseudomonas and Raoultella and four different species: Klebsiella oxytoca, Klebsiella variicola, Pseudomonas fluorescens and Raoultella planticola. Although some researchers have reported their performance under stress conditions, we are the first to report Klebsiella oxytoca, Klebsiella variicola and Raoultella planticola containing ACC deaminase under drought stress.The effects of a rhizospheric bacterium containing ACC deaminase(Raoultella planticola) on seed germination and regulation of glycine betaine(GB) metabolism under drought stress simulated by 15%(w/v) polyethylene glycol 6000(PEG-6000) were investigated in two maize(Zea mays L.) cultivars(Zheng Dan 958 and Jun Dan 20). In the present study, the seed germination rate was decreased in both cultivars under drought stress. However, it was improved due to the inoculum effect. Plants inoculated with Raoutella planticola exhibited greater concentration of GB and its precursor choline. At high drought levels, the inoculum caused a better response by the maize against the adverse effects of stress. The activity of PEAMT, CMO and BADH, functioning in the process of GB metabolism, correspondingly rose with the treatment of inoculum under drought condition. When stressed with PEG-6000, the inoculum-exposed plants exhibited similar trends of transcriptional level of PEAMT, CMO and BADH, especially the up-regulation of PEAMT, compared with ones without bacterial exposure.These findings are a reasonable explanation to their superb ability of causing stress-resistance in maize plants. The presence of diverse PGPR possessing potential ACC deaminase activity may be beneficial for enhancing crop production under different stress conditions.