The stability of ecosystem functions under changing environmental
conditions is often attributed to convergent functioning, where
different mechanisms lead to similar outcomes. In soil systems,
microbial activity is a major driver of nutrient cycling, yet it remains
unclear whether the presence of the same genes across taxa reliably
translates into redundant outcomes. We addressed this in microbial
phosphate solubilization, critical when applying alternative phosphorus
(P) fertilizers such as BCplus, a biochar-based fertilizer
from pyrolyzed animal bones coated with sulfur. Using multi-omics
analyses, we compared two soil isolates—Bacillus licheniformis COM1 and Psychrobacillus psychrodurans INOP01—alongside the reference strain B. velezensis DSM 23117. P. psychrodurans was excluded due to poor growth under P limitation. Despite similar growth and P mobilization, B. licheniformis and B. velezensis
relied on distinct strategies, indicating that mechanistically diverse
regulatory programs can yield convergent phosphate-solubilizing
outcomes. Transcriptional changes extended beyond P metabolism, with
both strains inducing nitrate reduction and adjusting sulfur metabolism,
underscoring tight coupling of P, nitrogen, and sulfur cycling. B. velezensis
responded rapidly by inducing Pho genes, organic acid production,
nitrate respiration, and plant growth–promoting traits including
indole-3-acetic acid biosynthesis. B. licheniformis instead
showed a slower adaptation marked by malate-driven acidification,
dissimilatory nitrate reduction to ammonium, and late riboflavin
activation. While both strains solubilized phosphate, their mechanisms
differed, illustrating that convergence at the functional outcome does
not imply similarity in regulation or metabolism. These results
highlight the need to account for strain-specific pathways when
developing microbial inoculants to optimize nutrient turnover in
low-input systems.