Mining the Microbiome of Key Species from African Savanna Woodlands: Potential for Soil Health Improvement and Plant Growth Promotion

(1) Aims: Assessing bacterial diversity and plant-growth-promoting functions in therhizosphere of the native African trees Colophospermum mopane and Combretum apiculatum in threelandscapes of the Limpopo National Park (Mozambique), subjected to two fire regimes. (2) Methods:Bacterial communities were identified through Illumina Miseq sequencing of the 16S rRNA geneamplicons, followed by culture dependent methods to isolate plant growth-promoting bacteria (PGPB).Plant growth-promoting traits of the cultivable bacterial fraction were further analyzed. To screen forthe presence of nitrogen-fixing bacteria, the promiscuous tropical legume Vigna unguiculata was usedas a trap host. The taxonomy of all purified isolates was genetically verified by 16S rRNA gene Sangersequencing. (3) Results: Bacterial community results indicated that fire did not drive major changesin bacterial abundance. However, culture-dependent methods allowed the differentiation of bacterialcommunities between the sampled sites, which were particularly enriched in Proteobacteria witha wide range of plant-beneficial traits, such as plant protection, plant nutrition, and plant growth.Bradyrhizobium was the most frequent symbiotic bacteria trapped in cowpea nodules coexisting withother endophytic bacteria. (4) Conclusion: Although the global analysis did not show significantdifferences between landscapes or sites with different fire regimes, probably due to the fast recoveryof bacterial communities, the isolation of PGPB suggests that the rhizosphere bacteria are drivenby the plant species, soil type, and fire regime, and are potentially associated with a wide range ofagricultural, environmental, and industrial applications. Thus, the rhizosphere of African savannahecosystems seems to be an untapped source of bacterial species and strains that should be furtherexploited for bio-based solutions.