Synergistic plant-microbe interactions drive the remediation of naphthenic acid fractional compounds in a constructed wetland mesocosm

Plant-root exudates support microbial communities, forming biocatalysts essential for the phytobioremediation of oil-contaminated sites. However, the structural complexity of naphthenic-acid-fraction compounds (NAFCs)--the primary toxic components in oil-sands process-affected water (OSPW)--pose a major challenge to effective treatment. While constructed wetland treatment systems (CWTSs) demonstrate potential for large-scale OSPW bioremediation, the synergistic roles of the host plant and root microbiome in NAFC degradation remain understudied. To address this, we used metatranscriptomics to evaluate shifts in microbial and plant functional gene expression in the roots of Typha latifolia grown in mesoscale CWTSs containing raw OSPW. The active root-microbial community was dominated by Pseudomonadota, which showed a slight increase with exposure to OSPW. Burkholderiales were the most active family, though their relative activity decreased in OSPW systems, where Flavobacteriaceae (Bacteroidota) activity increased. Clear microbial community shifts were driven by time and OSPW exposure. While the 18 previously identified microbial NAFC-degradation genes were not differentially expressed, 42 other genes with potential roles in NAFC or related organic compound degradation showed differential expression in OSPW-filled mesocosms compared to mesocosms-filled reverse-osmosis water at the same time points. This activity was dominated by specific oxidoreductases from Burkholderiales and Rhizobiales, whose roles had previously been predicted. Crucially, plant actively responded to NAFCs, robustly up-regulating genes encoding oxidoreductases, transporters, and glycosyltransferases, some with potential for NAFC degradation. Our findings provide an evidence that T. latifolia CWTSs drive efficient in-situ bioremediation through a synergistic plant-microbe partnership, coupling plant detoxification processes with specialized microbial catabolism for NAFC removal.