Rhizobacteria Mitigate the Negative Effect of Aluminum on Pea Growth by Immobilizing the Toxicant and Modulating Root Exudation

Abstract

High soil acidity is one of the main unfavorable soil factors that inhibit the growth and mineral nutrition of plants. This is largely due to the toxicity of aluminum (Al), the mobility of which increases significantly in acidic soils. Symbiotic microorganisms have a wide range of beneficial properties for plants, protecting them against abiotic stress factors. This report describes the mechanisms of positive effects of plant growth-promoting rhizobacteria Pseudomonas fluorescens SPB2137 on four pea (Pisum sativum L.) genotypes grown in hydroponics and treated with 80 µM AlCl3. In batch culture, the bacteria produced auxins, possessed 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity, alkalized the medium and immobilized Al, forming biofilm-like structures and insoluble phosphates. Inoculation with Ps. fluorescens SPB2137 increased root and/or shoot biomass of Al-treated plants. The bacteria alkalized the nutrient solution and transferred Al from the solution to the residue, which contained phosphorus that was exuded by roots. As a result, the Al concentration in roots decreased, while the amount of precipitated Al correlated negatively with its concentration in the solution, positively with the solution pH and negatively with Al concentration in roots and shoots. Treatment with Al induced root exudation of organic acids, amino acids and sugars. The bacteria modulated root exudation via utilization and/or stimulation processes. The effects of Al and bacteria on plants varied depending on pea genotype, but all the effects had a positive direction and the variability was mostly quantitative. Thus, Ps. fluorescens SPB2137 improved the Al tolerance of pea due to immobilization and exclusion of toxicants from the root zone.

Application of Associative Rhizobacteria for Increasing the Soft Wheat Productivity and Reducing the Diseases Harmfulness

“…The observed wheat growth promotion by Ps. fluorescens SPB2137 was probably due its ability producing auxins and possessing ACC deaminase activity, which was recently demonstrated on pea plants (Belimov et al, 2022). Strains B. subtilis 124-11 and Sphinhomonas sp.…”

Beneficial aluminium immobilizing microorganisms inhabiting the rhizosphere of pea

“…L30 (MIC and MLC equal to 5 and 30 mg Al L -1 , respectively) improving Al tolerance of barley plants (Belimov, Kunakova, and Gruzdeva, 1998) and Ps. fluorescens SPB2137 (MIC equal to 5 mg Al L -1 ) improving Al tolerance of pea plants (Belimov et al, 2022).…”

“…Recently we showed that PGPR Pseudomonas fluorescens strain SPB2137, initially selected as a biocontrol bacterium (Shaposhnikov et al, 2019), improved Al tolerance of pea due to immobilization and exclusion of this toxicant from root zone (Belimov et al, 2022). Although this strain immobilized Al, produced auxins and possessed ACC deaminase activity, it was relatively sensitive to Al, and its effects on plants were sometimes insignificant.…”

“…The GEN III MicroPlate™ test panel with Microbial Identification Systems software OmniLog® Data Collection (Biolog, Inc., Hayward, USA) was used to obtain a phenotypic pattern and additional identification of bacteria. Utilization of some components (citric, fumaric, lactic, malic, pyruvic and succinic acids, glucose and fructose) playing an important role in Al detoxication by plant root exudates (Ma, Ryan, and Delhaize, 2001;Belimov et al, 2022), and pH of the batch cultures supplemented with these substances as a sole source of carbon, were determined as previously described (Kuzmicheva et al, 2017).…”

Draft Genome Sequence of the Bacterium Cupriavidus sp. Strain D39, Inhabiting the Rhizosphere of Pea Plants (Pisum sativum L.)

“…Plants growing in acidic soils suffer from elevated concentrations of mobile aluminum ions ( 1 ). An essential feature of the species Cupriavidus basilensis is its ability to resist toxic metals ( 2 – 4 ) and degrade xenobiotics ( 5 – 7 ).…”