Microbial metabolic remodeling under the electric field: A CUE-centered mechanism for enhanced petroleum bioremediation

Abstract

This study explores how bio-electrokinetic remediation (BIO-EK) enhances pollutant degradation by modulating carbon use efficiency (CUE) and microbial functionality. After 100 d, the BIO-EK group achieved a 55.8 ± 1.8% (n = 3) total petroleum hydrocarbon (TPH) degradation rate, significantly higher than bioremediation (BIO, 39.3 ± 2.0%, n = 3) and electrokinetics (EK, 38.7 ± 1.4%, n = 3), with total carbon (TC) content decreasing from 5.0 ± 0.03% (n = 3) to 3.5 ± 0.03% (n = 3), demonstrating its superior pollutant removal effectiveness. Correspondingly, its microbial CUE increased by 1.2-2.4 times, demonstrating that electrokinetic treatment shifted carbon allocation from respiration to biomass synthesis, which was supported by substantially higher microbial biomass and growth rates. Functionally, electrokinetic treatment enriched the abundance of genes for degrading alkanes, fatty acids, and PAHs, activating core metabolic routes such as β-oxidation and the TCA cycle. This was specifically manifested as a marked increase in the abundance of genes encoding pivotal enzymes and their inferred metabolic potential, particularly those related to medium-chain alkane β-oxidation and aromatic hydrocarbon ring cleavage. Structural equation modeling (SEM) revealed that electrokinetic treatment reversed the metabolic trade-off between CUE and degradation in the BIO group, enabling microbes to allocate carbon to both growth and degradation simultaneously. It also showed that electrokinetics enhanced the statistical associations between soil properties, functional genes, and TPH removal, consistent with the proposed causal model. Thus, BIO-EK establishes a highly efficient degradation pathway through the synergistic regulation of environment, genetics, and microbial metabolism.