The Effect of Two Siderophore-Producing Bacillus Strains on the Growth Promotion of Perennial Ryegrass under Cadmium Stress

Author:

Wu Lingling1ORCID,Xie Yongli123,Li Junxi1,Han Mingrong1,Yang Xue12,Chang Feifei1

Affiliation:

1. College of Agriculture and Animal Husbandry, Qinghai University, Xining 810016, China

2. State Key Laboratory of Plateau Ecology and Agriculture, Qinghai University, Xining 810016, China

3. Key Laboratory of Use of Forage Germplasm Resources on Tibetan Plateau of Qinghai Province, Qinghai University, Xining 810016, China

Abstract

Cadmium (Cd) is a highly toxic and cumulative environmental pollutant. Siderophores are heavy metal chelators with high affinity to heavy metals, such as Cd. Ryegrass (Lolium perenne L.) has a potential remediation capacity for soils contaminated by heavy metals. Consequently, using ryegrass alongside beneficial soil microorganisms that produce siderophores may be an effective means to remediate soils contaminated with Cd. In this study, the Bacillus strains WL1210 and CD303, which were previously isolated from the rhizospheres of Nitraria tangutorum in Wulan and Peganum harmala L. in Dachaidan, Qinghai, China, respectively, both arid and sandy environments, were evaluated for heavy metal pollution mitigation. Our quantitative analyses have discerned that the two bacterial strains possess commendable attributes of phosphorus (P) solubilization and potassium (K) dissolution, coupled with the capacity to produce phytohormones. To assess the heavy metal stress resilience of these strains, they were subjected to a cadmium concentration gradient, revealing their incremental growth despite cadmium presence, indicative of a pronounced tolerance threshold. The subsequent phylogenetic analysis, bolstered by robust genomic data from conserved housekeeping genes, including 16S rDNA, gyr B gene sequencing, as well as dnaK and recA, delineated a species-level phylogenetic tree, thereby confirming the strains as Bacillus atrophaeus. Additionally, we identified the types of iron-carrier-producing strains as catechol (WL1210) and carboxylic acid ferrophilin (CD303). A genomic analysis uncovered functional genes in strain CD303 associated with plant growth and iron carrier biosynthesis, such as fnr and iscA. Ryegrass seed germination assays, alongside morphological and physiological evaluations under diverse heavy metal stress, underscored the strains’ potential to enhance ryegrass growth under high cadmium stress when treated with bacterial suspensions. This insight probes the strains’ utility in leveraging alpine microbial resources and promoting ryegrass proliferation.

Funder

Applied Basic Research Project of Qinghai Provincial Science and Technology Department

National Natural Science Foundation of China

Publisher

MDPI AG

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