Isolation, identification, and characterization of novel, aluminium tolerant rhizobia strains from Kenyan soil

The agricultural sector is the cornerstone of Kenya’s economy. It employs about 40% of Kenya’s population, more than 70% in rural areas, and contributes to about 33% of Kenya’s gross domestic product (GDP). Kenya’s vision 2030 identifies agriculture, including common bean cultivation, as one of the main pillars that will play a role in achieving sustainable 10% annual GDP. However, the main impediment to realizing this goal is the high cost of fertilizer which is not affordable for most farmers. An alternative to nitrogenous fertilizers is the application of rhizobia for common bean production, which converts atmospheric dinitrogen to reduced ammonium, suitable for plant use. Inoculant formulations must include local elite rhizobia because they can compete with the indigenous rhizobia in the soil and tolerate the harsh conditions in Kenyan soils. I isolated three nitrogen-fixing rhizobia (B3, S2, and S3) from these soils. In greenhouse experiments, plants infected with these rhizobia produced more biomass and accumulated more nitrogen than uninoculated plants and plants inoculated with a commercial strain CIAT899 which Kenyan farmers widely use. The biomass of the plants infected by either of the three isolates was comparable to that of plants supplied with nitrogenous fertilizer. Field experiments in Kenya demonstrated that the seed dry weight of plants inoculated with S3 was significantly higher than that of all other plants. S3 conferred more benefits to the plants than S2 and B2 and the commercial strain CIAT899. Kenyan soil faces detrimental abiotic stresses, particularly low pH and the toxic metallic ion Al. The three isolates were better adapted to low pH and Al toxicity than CIAT899. Isolate B3 grew in media with pH 4.8, a pH that was detrimental to the commercial isolate CIAT899. Short-term viability assays and long-term recovery experiments demonstrated that B3 performs better under Al stress than CIAT899. Al did not only bind to the rhizobia membran

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

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

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

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

Genetic Diversity of Cowpea (Vigna unguiculata (L.) Walp.) Accession in Kenya Gene Bank Based on Simple Sequence Repeat Markers

Increased agricultural production is an urgent issue. Projected global population is 9 million people by mid of this century. Estimation projects death of 1 million people for lack of food quality (micronutrient deficit) and quantity (protein deficit). Majority of these people will be living in developing countries. Other global challenges include shrinking cultivable lands, salinity, and flooding due to climate changes, new emerging pathogens, and pests. These affect crop production. Furthermore, they are major threats to crop genetic resources and food security. Genetic diversity in cultivated crops indicates gene pool richness. It is the greatest resource for plant breeders to select lines that enhance food security. This study was conducted by Masinde Muliro University to evaluate genetic diversity in 19 cowpea accessions from Kenya national gene bank. Accessions clustered into two major groups. High divergence was observed between accessions from Ethiopia and Australia and those from Western Kenya. Upper Volta accessions were closely related to those from Western Kenya. Low variation was observed between accessions from Eastern and Rift Valley than those from Western and Coastal regions of Kenya. Diversity obtained in this study can further be exploited for the improvement of cowpea in Kenya as a measure of food security