| Summary: | Total and diazotrophic bacteria were assessed in the rhizosphere soils of native and encroaching legumes growing in the Succulent Karoo Biome (SKB), South Africa. These were <i>Calobota sericea</i>, <i>Lessertia diffusa</i>, <i>Vachellia karroo</i>, and <i>Wiborgia monoptera</i>, of Fabaceae family near Springbok (Northern Cape Province) and neighboring refugia of the Fynbos biome for <i>C. sericea</i> for comparison purposes. Metabarcoding approach using 16S rRNA gene revealed <i>Actinobacteria</i> (26.7%)<i>, Proteobacteria</i> (23.6%)<i>, Planctomycetes,</i> and <i>Acidobacteria</i> (10%), while the <i>nifH</i> gene revealed <i>Proteobacteria</i> (70.3%) and <i>Cyanobacteria</i> (29.5%) of the total sequences recovered as the dominant phyla. Some of the diazotrophs measured were assigned to families; <i>Phyllobacteriaceae</i> (39%) and <i>Nostocaceae</i> (24.4%) (all legumes), <i>Rhodospirillaceae</i> (7.9%), <i>Bradyrhizobiaceae</i> (4.6%) and <i>Methylobacteriaceae</i> (3%) (<i>C. sericea</i>, <i>V. karroo</i>, <i>W. monoptera</i>)<i>, Rhizobiaceae</i> (4.2%; <i>C. sericea, L. diffusa, V. Karroo</i>), <i>Microchaetaceae</i> (4%; <i>W. monoptera</i>, <i>V. karroo</i>), <i>Scytonemataceae</i> (3.1%; <i>L. diffusa, W. monoptera</i>), and <i>Pseudomonadaceae</i> (2.7%; <i>V. karroo</i>) of the total sequences recovered. These families have the potential to fix the atmospheric nitrogen. While some diazotrophs were specific or shared across several legumes, a member of <i>Mesorhizobium</i> species was common in all rhizosphere soils considered. <i>V. karroo</i> had statistically significantly higher Alpha and distinct Beta-diversity values, than other legumes, supporting its influence on soil microbes. Overall, this work showed diverse bacteria that support plant life in harsh environments such as the SKB, and shows how they are influenced by legumes.
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