Chimwamurombe, P. M. | bioRxiv Science

bioRxiv2025

Bacterial community studies and novel Bradyrhizobium and Rhizobium strains from drought-tolerant legumes grown in Namibia

AimsAnalysis of the microbiota associated with root nodules of five species of drought-tolerant legumes grown in Namibia. These legumes were Lablab purpureus, Vigna radiata, Vigna unguiculata, Macrotyloma uniflorum, and Vigna aconitifolia. Methods16S rRNA gene amplicon sequencing analysis and isolation of rhizobial and non-rhizobial bacterial strains from root nodules was performed. Plant growth-promoting traits were assessed on some isolates and the genomes of four rhizobial strains were sequenced. ResultsThe microbiota analysis revealed Bradyrhizobium as the most prevalent genus in the root nodules, while most of the non-rhizobial community included members of Bacillus genus. In addition, a strain of Variovorax paradoxus was also isolated from V. unguiculata, representing the first documented isolation and characterization report in Namibia. In vitro phenotypic characterization of the non-rhizobial nodule endophytes indicated that they possessed several plant growth-promoting traits. The four rhizobial strains isolated were taxonomically affiliated to the genera Bradyrhizobium and Rhizobium. Genome sequencing revealed that these strains possibly belong to novel species since they share only a limited similarity (dDDH values<70%) to already known species. Impact StatementThis study demonstrated that drought-tolerant legume species harbour microbial diversity from Namibian soil, which allowed us to increase our knowledge on plant-associated bacteria and their possible use in sustainable farming systems, as potential bioinoculants for crop production and for soil revitalization. Utilizing locally isolated bacterial strains as microbial bioinoculants maximizes their compatibility with the local conditions increasing the potential for positive effects on plant health and ecosystem functioning.

microbiology↗

bioRxiv2022

Isolation and molecular identification of endophytic bacteria from Tylosema esculentum

Tylosema esculentum is a perennial legume that is predominant in Namibia, Botswana, and South Africa. It is rich in nutrients, drought-tolerant, and a climate change contender for future agriculture. The objectives of this study were to isolate and identify culturable bacterial endophytes. Our study assessed the mean CFUs/mL among the tuberous roots, stems, and leaves to determine the density and diversity using ANOVA. It was a quantitatively controlled experiment in which seeds were grown in a greenhouse. The bacteria number varied from 1.29 x 108 to 3.5 x 108 CFU/ml of broth, with the highest in the tuberous roots and the lowest in the leaves. At a 5% significant level, we revealed that there is a difference among the bacterial densities of the plant parts. Shannon-Weiner diversity showed that there is a higher diversity of bacteria in the tuberous roots. Of the isolates that were obtained, 53.8% belonged to Enterobacter, 15.4% to Bacillus, 15.4% to Pantoea, and 7.67% to Burkholderia. These discoveries have made us more aware of the endophytic bacteria we now have. These strains might thus be used in food crops to boost productivity, enabling food security, especially in Africa. The significance of the isolates in biological control, agriculture, and biotechnology for growth promotion will be determined by further research.

microbiology↗