Rhizosphere Diazotrophs and Other Bacteria Associated with Native and Encroaching Legumes in the Succulent Karoo Biome in South Africa

Abstract

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 Calobota sericea, Lessertia diffusa, Vachellia karroo, and Wiborgia monoptera, of Fabaceae family near Springbok (Northern Cape Province) and neighboring refugia of the Fynbos biome for C. sericea for comparison purposes. Metabarcoding approach using 16S rRNA gene revealed Actinobacteria (26.7%), Proteobacteria (23.6%), Planctomycetes, and Acidobacteria (10%), while the nifH gene revealed Proteobacteria (70.3%) and Cyanobacteria (29.5%) of the total sequences recovered as the dominant phyla. Some of the diazotrophs measured were assigned to families; Phyllobacteriaceae (39%) and Nostocaceae (24.4%) (all legumes), Rhodospirillaceae (7.9%), Bradyrhizobiaceae (4.6%) and Methylobacteriaceae (3%) (C. sericea, V. karroo, W. monoptera), Rhizobiaceae (4.2%; C. sericea, L. diffusa, V. Karroo), Microchaetaceae (4%; W. monoptera, V. karroo), Scytonemataceae (3.1%; L. diffusa, W. monoptera), and Pseudomonadaceae (2.7%; V. karroo) 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 Mesorhizobium species was common in all rhizosphere soils considered. V. karroo 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.

Evolution of novel strains of Ensifer nodulating the invasive legume Leucaena leucocephala (Lam.) de Wit in different climatic regions of India through lateral gene transfer

“…DISCUSSION Introduction and naturalization of an exotic nodulating legume Leucaena and its accompanying microsymbionts in a new geographical areaBio-geographical variations have been observed in the distribution of nodulated legumes and their nitrogenfixing microsymbionts(Sprent et al 2017). When a species is introduced to a new site its survival and on various edaphic and climatic factors, its tolerance to environmental stresses, and the occurrence of potential pathogens and predators at the new site(Kamutando et al 2019;Muema et al 2022).…”