Yaya Anianhou Ouattara

Rhizobia are a polyphyletic group of Proteobacteria comprising approximately 700 different species. Despite significant advancements in their taxonomy, evolutionary history, and ecological importance, substantial knowledge gaps remain regarding a detailed understanding of rhizobial biodiversity in a geographical context and the interest in studying and valorizing native rhizobial strains. This bibliometric study used data from the last four decades (1985–2025) to review the taxonomic and functional diversity of the documented novel taxa of rhizobia described from African ecosystems, as well as their valorization status as biofertilizers. It aims to discuss the interest in knowing, preserving, and valorizing native rhizobial resources in the global context of climate change and biodiversity erosion. The study revealed that the first African indigenous novel species of rhizobia was published in 1988, although research on rhizobia dates back to the 1950s in Africa. To date, ~63 species (approximately 9% of the total in the world) and two genera of rhizobia have been described using native isolates from 11 African countries, with substantial discoveries from the Succulent Karoo hotspot of biodiversity in South Africa. Approximately 51% of species are affiliated with Bradyrhizobium and Mesorhizobium, with Vachellia karroo and Senegalia spp. (formerly Acacia spp.) as their primary hosts. Most species-type strains (~89%) were found to be infective on legumes and are good candidates for biofertilizer development. However, there is a limited level of commercial valorization of indigenous isolates as inoculants, mainly because the production of biological intrants is still at the experimental stage in Africa. Interestingly, important breaking point discoveries have been made using native rhizobial strains from Africa, including the pioneering demonstration in 2001 that Burkholderia (beta-rhizobia) is a symbiotic genus with legumes. It also includes the discovery of stem-nodulating rhizobia and Nod factor-independent symbiotic processes in some rhizobia. Together, this review highlights the importance of native African rhizobial strains. This underscores the need to accelerate their agronomic valorization to better support the transition to more resilient and sustainable legume-based farming systems in African countries.

Côte d’Ivoire has the largest cashew tree cultivation area in the world, but the cashew apple produced is still underutilized despite its potential for industrial use. The present study aimed to isolate and identify acetic acid bacterial strains and assess their potential use for cashew apple-based vinegar production. Vinegar mother from fermented juice was used to isolate acetic acid bacteria on a standard glucose-based medium. Physiological and biochemical tests followed by 16S rRNA gene analysis and phylogeny were used for isolate characterization. Moreover, their acetic acid production capacity was assessed. As results, five strains of the Acetobacter genus were isolated. Phenotypic and phylogenetic analysis revealed that four of them, namely OYA2, OYA6, OYA9, and OYA10, belong to the A. tropicalis/A. senegalensis species complex with 99.7% or 100% similarity. The fifth strain, OYA7, being similar (99.7%) to A. syzygii. All the isolates were resistant to alcohol 15% (v/v) and grew well between pH 5.0 and 6.5. Their optimal growth temperatures varied between 27 °C and 37 °C, and only isolate OYA6 grew at a temperature of up to 40 °C. They produced vinegar with a yield (Y_p/s, g/g) varying from 0.82 to 0.92, and acetic acid contents (g/L) of 80.67, 70.26, 70.11, 68.70 and 67.22 were obtained with OYA6, OYA7, OYA2, OYA10, and OYA9, respectively. Thus, the isolate OYA6 appeared as the best candidate for vinegar production, owing to its superior yield and thermotolerance abilities that need to be further explored for industry use.

Côte d’Ivoire has the main cashew tree culture area worldwide, but the cashew apple produced is still underutilized although its potential for industry. In the present study, the aim was to isolate and identify acetic acid bacterial strains, and to assess their potential use for cashew apple-based vinegar production. Vinegar mother from fermented juice was used to isolate acetic acid bacteria on a standard glucose-based medium. Physiological and biochemical tests followed by 16S rRNA gene analysis and phylogeny were used for isolate characterization. Moreover, their acetic acid production capacity was assessed. As results, five (05) strains of the Acetobacter genus were isolated. Phenotypic and phylogenetic analysis revealed that four of them, namely OYA2, OYA6, OYA9, and OYA10, belong to A. tropicalis / A. senegalensis species complex with 99,7% or 100% similarity. The last strain, OYA7, match to A. syzygii (99,7%). All the isolates were resistant to 15° alcohol (v/v) and grew well between pH 5.0 and 6.5. Their optimal growth temperatures varied between 27°C and 37°C, and only isolate OYA6 grows up to 40°C. They produced vinegar with yield (Yp/s , g/g) varying from 0.82 to 0.92, and acetic acid content (g/L) of 80.67 ± 2.1, 70.26 ± 0.9, 70.11 ± 1.7, 68.70 ± 1.5 and 67.22 ± 0.40 were obtained with OYA6, OYA7, OYA2, OYA10, and OYA9, respectively. Thus, the isolate OYA6 appeared as the best candidate for vinegar production, owing to its superior yield and thermotolerance ability that need to be further explored for industry use purpose.