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.