Isolation and identification of growth-promoting bacteria in halophyte rhizosphere in arid region and their growth- promoting characteristics under drought and salt stresses

Abstract:

[Objective] We isolated and screened microbes with growth-promoting function and salt tolerance from the rhizosphere soil of halophytes in dry and saline habitats and studied their growth-promoting ability, hoping to provide high-quality bacterial resources and a reference for alleviating soil salinization in arid areas. [Methods] Strains with salt tolerance and phosphate-solubilizing and potassium-releasing abilities were screened with selective media. Then, the ability of the strains to produce indole-3-acetic acid (IAA), 1-aminocyclopropane-1-carboxylate (ACC) deaminase, siderophore, and exopolysaccharide was tested. Through antagonism test, strains with excellent functions and no antagonism to each other were selected to prepare the compound bacterial mixture. The suspension of each of the strains and that of the mixture of strains without antagonism to each other were respectively used to infect seeds of radish and maize, and the influence on seed germination rate under salt stress and plant growth under both drought and salt stresses was observed. Finally, 16S rRNA gene sequencing was performed to identify the strains. [Results] Strains yl923, hs032, and hy127 with salt tolerance and growth-promoting ability were screened out. yl923 can solubilize phosphate (46.29 mg/L), help release potassium (58.07 mg/L), and produce IAA (29.23 mg/L), ACC deaminase (13.83 U/mg), and siderophores (SU=0.43). hs032 was outstanding in producing IAA (61.18 mg/L) and siderophore (SU=0.23) and hy127 excelled in producing ACC deaminase (15.29 U/mg). Through 16S rRNA gene sequencing, yl923 and hs032 were identified as Bacillus subtilis and hy127 was determined to be Priestia megaterium. The three showed no antagonism to each other and thus they can be used together as compound bacterial mixture. The 2% mixture suspension can improve the seed germination rate (77%) under salt stress. Moreover, it can increase the root length, plant height, dry weight, and chlorophyll production (P<0.05), and significantly reduce the malondialdehyde (MDA) content (60%) of maize under drought and salt stresses. [Conclusion] Strains yl923, hs032 and hy127 show excellent salt tolerance and growth-promoting function. The compound mixture prepared with the three can remarkably promote plant growth under drought and salt stresses and those strains have the potential to improve salinized soil in arid regions.