Identification of four plant growth-promoting rhizobacteria isolated from tea rhizosphere

Abstract:

[Background] Plant growth-promoting rhizobacteria can promote plant growth and improve stress tolerance. There are special microbial habitats on tea rhizosphere and some beneficial microorganisms with growth-promoting effects could be easily acquired. [Objective] To ascertain taxonomic status and study growth-promoting characteristics of four PGPR strains isolated from tea rhizosphere, and further screen superior PGPR strain. [Methods] These four strains were identified based on morphological, physiological and biochemical characteristics, homology alignments of 16S rRNA gene sequences. The plant growth-promoting characteristics of isolates were studied. Phosphorus contents were analyzed with Mo-Sb colorimetry. ACC (1-Aminocyclopropane-1-carboxylic acid) deaminase activity was measured by colorimetric method. Also, siderophere secreting capacity and IAA content were determined by quantitative test of CAS (Chrome zaurol S) medium and method of Salkowski, respectively. In pot experiments, plant growth-promoting effects were analyzed by measuring shoot heights and fresh weights of tested plants (including Chinese cabbage, swamp cabbage, amaranth and rice). [Results] The strain KKS-6-N1 was identified as Agrobacterium radiobacter, KKS-7-N7 identified as Pseudomonas aeruginosa, GD3 identified as Pseudomonas hunanensis, and GD12 identified as Bacillus flexus, respectively. In these four strains, nitrogen-fixing strains KKS-6-N1 and KKS-7-N7 produced siderophore, KKS-7-N7 also had the abilities of phosphorus-dissolving and IAA secreting as high as 101.29 mg/L. The other two strains, potassium-solubilizing strain GD3 still dissolved phosphorus, its ACC deaminase activity was 8.09 μmol/(mg·h) and relative content of siderophore was 0.31. whereas GD12, which had dissolved potassium and fixed nitrogen, was found to secret ACC deaminase of 14.46 μmol/(mg·h). In pot experiments, shoot heights and fresh weights of Chinese cabbage, swamp cabbage and amaranth were increased obviously by inoculation of these four strains, especially GD3 is the most excellent among them. [Conclusion] Pseudomonas hunanensis GD3, which isolated from tea rhizosphere, could strongly promote plant growth. And it is possible to develop as an excellent microbial fertilizer.