The Cell Membrane of a Novel Rhizobium phaseoli Strain Is the Crucial Target for Aluminium Toxicity and Tolerance.

Clabe Wekesa,Ralf Oelmüller,Alexandra C U Furch,George O Asudi,Michael Reichelt,John O Muoma

doi:10.3390/cells11050873

Clabe Wekesa, Ralf Oelmüller + Show 4 more

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https://doi.org/10.3390/cells11050873

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Abstract

Soils with low pH and high aluminium (Al) contamination restrict common bean production, mainly due to adverse effects on rhizobia. We isolated a novel rhizobium strain, B3, from Kenyan soil which is more tolerant to Al stress than the widely used commercial strain CIAT899. B3 was resistant to 50 µM Al and recovered from 100 µM Al stress, while CIAT899 did not. Calcein labeling showed that less Al binds to the B3 membranes and less ATP and mScarlet-1 protein, a cytoplasmic marker, leaked out of B3 than CIAT899 cells in Al-containing media. Expression profiles showed that the primary targets of Al are genes involved in membrane biogenesis, metal ions binding and transport, carbohydrate, and amino acid metabolism and transport. The identified differentially expressed genes suggested that the intracellular γ-aminobutyric acid (GABA), glutathione (GSH), and amino acid levels, as well as the amount of the extracellular exopolysaccharide (EPS), might change during Al stress. Altered EPS levels could also influence biofilm formation. Therefore, these parameters were investigated in more detail. The GABA levels, extracellular EPS production, and biofilm formation increased, while GSH and amino acid level decreased. In conclusion, our comparative analysis identified genes that respond to Al stress in R. phaseoli. It appears that a large portion of the identified genes code for proteins stabilizing the plasma membrane. These genes might be helpful for future studies investigating the molecular basis of Al tolerance and the characterization of candidate rhizobial isolates that perform better in Al-contaminated soils than commercial strains.

Highlights

Common bean (Phaseolus vulgaris) is a major food worldwide
The molecular basis of nodule formation and N fixation has been well investigated in the last decades [3–5], much less is known about abiotic stresses that inhibit symbiosis
Growth in Al-containing media was compared for three rhizobia strains from WestGrowth in Al-containing media was compared for three rhizobia strains from Western ern Kenya (S3 and two previously isolated R. phaseoli strains B3 and S2) [31] and the comKenya (S3 and two previously isolated R. phaseoli strains B3 and S2) [31] and the commercial mercial strain CIAT899

Summary

Introduction

The world consumption of common beans reached 2.51 kg per person in 2018 [1], an ~8% increase compared to 2008. As a legume, it forms symbiotic relationships with rhizobial bacteria, which enables the conversion of free atmospheric nitrogen (N) to ammonium, reducing the overutilization of N fertilizers in agriculture. Herridge et al [2] demonstrated that the rhizobia fix between 50 and 70 million tonnes of N per year. They colonize the roots of the legumes and form nodules, which harbor oxygen-sensitive nitrogenase. The molecular basis of nodule formation and N fixation has been well investigated in the last decades [3–5], much less is known about abiotic stresses that inhibit symbiosis

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