Contribution of Microbial Metabolism to Geogenic Phosphorus Enrichment in Groundwater: Insights from Metagenomic Sequencing and Organic Molecular Characterization

Microbial mediation in the enrichment of geogenic phosphorus (P) is often mentioned but rarely explored, especially in P enrichment processes through the mineralization of dissolved organic matter (DOM) containing natural P. To bridge the theoretical gap, this study investigated the mechanisms of P enrichment through microbially mediated mineralization of natural P-containing DOM by adopting an approach combining comprehensive field investigation with hydrochemical and molecular biological analyses. The co-analysis of the dominant microbial community compositions and genomics revealed that the microbial metabolism pathways involved in the biodegradation of P-containing DOM were associated with the enrichment level of dissolved inorganic phosphorus (DIP). Specifically, dephosphorylation was more pronounced under conditions of limited DIP, while C–P bond cleavage was the primary metabolic pathway under sufficient DIP. Co-occurrence network analysis further indicated that the substrates for DIP enrichment differed between dephosphorylation and C–P bond cleavage, namely CHONSP₁ compounds in the region of highly unsaturated-low O compounds (AI ≤ 0.5, H/C < 1.5, and O/C < 0.4) and CHOP₁ compounds in the region of highly unsaturated-high O compounds (AI ≤ 0.5, H/C < 1.5, and O/C ≥ 0.4), respectively. These findings provide new insights into geogenic P enrichment in groundwater from the perspective of microbial metabolism and have potential implications for the bioremediation of P-contaminated groundwater at different contamination levels.