Novel primers for quantification of Priestia megaterium populations in soil using qPCR

Priestia megaterium is a plant growth-promoting bacterium and a common component of some agricultural microbial inoculants. However, the functional effect of P. megaterium additions to farm soils rests on the ability of the applied cells to survive introduction and may be reduced if native P. megaterium populations are already present. To address the need to quantify P. megaterium populations within diverse soil microbiomes, we developed a novel qPCR primer set that targets P. megaterium. We demonstrate the specificity of our primers towards P. megaterium and show a dynamic range of detection, ranging from ~5 × 10²–1 × 10⁸ CFU g⁻¹ dry soil. Using these primers, we then conducted a soil mesocosm experiment tracking the fate of P. megaterium inoculated into three soils with varying physiochemical properties. After two weeks, inoculated populations had significantly declined in all three soils, but at different rates and magnitudes. In one soil, P. megaterium abundance was indistinguishable between inoculated and uninoculated mesocosms after only ten days. Our results demonstrate the effectiveness of this qPCR primer set for the specific and sensitive quantification of P. megaterium, and highlight the variable performance of this bacterium when inoculated into different soil environments.