Hidden Partners in Diversity: Acidobacteriota and Their Distribution in the Cape Floristic Region

The Cape Floristic Region, a biodiversity hotspot in South Africa, is characterised by acidic, nutrient-poor soils and distinctive fynbos vegetation. Despite the ecological importance and metabolic versatility of Acidobacteriota, their diversity and functional roles in fynbos soils remain poorly understood. This study investigated the diversity and abundance of Acidobacteriota in two nature reserves, Jonkershoek and Kogelberg, and the influence of soil abiotic factors and enzyme activities on their distribution and composition at the subdivision (SD) level. A total of 26 bulk soil samples were collected, and the V1-V9 regions of the 16S rRNA gene were sequenced using the Oxford Nanopore platform. The mean relative abundance of Acidobacteriota ranged from 1.5% to 36.25%. Subdivision 1 was the most dominant, with relative abundances of 66.96 ± 8.96% in Kogelberg Nature Reserve and 30.35 ± 0.15% in Jonkershoek Nature Reserve (p = 0.001). Other prevalent SDs included SDs 2, 3, and 5, with this study being the first to report the presence of SDs 22 and 17 in fynbos soils. Beta-diversity analysis revealed distinct community compositions between the two reserves, driven by soil pH, moisture content, available phosphate, electrical conductivity, and enzyme activities (p = 0.001). Several positive and negative correlations between Acidobacteriota SDs and soil properties were also identified. Overall, this study highlights the high diversity of Acidobacteriota in fynbos soils and their close associations with soil abiotic properties, underscoring the need for cultivation-based research to elucidate their ecological roles in these oligotrophic environments.