Isolation,identification,and characterization of a cadmium-tolerant bacterium Achromobacter sp.A81 with plant growth-promoting effect
[Objective]To screen and identify cadmium(Cd)-tolerant bacteria with plant growth-promoting effect from contaminated soil of a mining area in Guangxi,characterize the strain screened out in terms of the Cd tolerance,Cd2+removal efficiency,plant growth-promoting effect,and influence on rice growth under Cd stress,and demonstrate the potential of the strain in plant growth and soil remediation.[Methods]Cd-tolerant bacteria were isolated by the dilution coating method and Cd2+concentration gradient acclimation and further identified based on the morphological,physiological,biochemical characteristics and the 16S rRNA gene phylogenetic tree.The Cd tolerance,Cd2+removal efficiency,and plant growth-promoting effect of the target strain were measured by microdilution,inductively coupled plasma mass spectrometry,and colorimetry.Finally,the effect of the strain on the growth of rice plants under Cdstress was investigated by a pot experiment.[Results]Twelve strains of bacteria with good tolerance to Cd2+were isolated from heavy metal-contaminated soil,and one strain with the best tolerance to Cd was identified as Achromobacter sp.A81,which could grow in the presence of 800 mg/L Cd2+.Strain A81 cultured with 10 mg/L Cd2+for 7 days showed the maximum Cd2+removal rate of 44.66％.Both the supernatant and cells of strain A81 demonstrated the ability to adsorb Cd2+.Under Cd stress,the strain secreted a large amount of extracellular polymeric substances(EPS)primarily composed of insoluble and soluble proteins.Furthermore,this strain was capable of fixing nitrogen,solubilizing phosphorus,and secreting siderophores,indole-3-acetic acid(IAA),and 1-aminocyclopropane-L-carboxylate(ACC)deaminase,demonstrating remarkable plant growth-promoting effect.Pot experiment results revealed that compared with the group subjected to Cd stress,the rice plants inoculated with strain A81 showed increases of 9.08％,39.59％,41.94％,and 73.58％in plant height,root length,stem diameter,and fresh weight,respectively.[Conclusion]This study investigated the Cd tolerance,Cd removal efficiency,and plant growth-promoting effect of Achromobacter sp.A81 and assessed the application potential of this strain in Cd-contaminated soil remediation,providing a scientific basis and high-quality strain resources for the microbial remediation of heavy metal pollution and green agricultural development.
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