Combination of plant-growth-promoting and fluoranthene-degrading microbes enhances phytoremediation efficiency in the ryegrass rhizosphere

Plant- and/or microbe-based systems can provide a cost-effective, sustainable means to remove contaminants from soil. Microbe-assisted phytoremediation has potential utility for polycyclic aromatic hydrocarbons such as fluoranthene (Flu) removal from soils; however, the efficiency varies with the plant and microbes used. This study evaluated the Flu removal efficiency in a system with ryegrass (Lolium multiflorum), an IAA-producing Arthrobacter pascens strain (ZZ21), and/or a Flu-degrading Bacillus cereus strain (Z21). Strain ZZ21 significantly enhanced the growth of ryegrass. Ryegrass in combination with both strains (FIP) was the most effective method for Flu removal. By day 60, 74.9% of the Flu was depleted in the FIP treatment, compared with 21.1% in the control (CK), 63.7% with ryegrass alone (P), 69.0% for ryegrass with ZZ21 (IP), and 72.6% for ryegrass with Z21 (FP). FIP treatment promoted ryegrass growth, accelerated Flu accumulation in plants, and increased soil microbial counts. Microbial carbon utilization was significantly higher in soil in the FIP than with the CK treatment. Principal component analysis of the distribution of carbon substrate utilization showed that microbial functional profiles diverged among treatments, and this divergence became more profound at day 60 than day 30. Microbial inoculation significantly enhanced microbial utilization of phenols. Microbes in the FIP soil dominantly utilized amines/amides and phenols at day 30 but shifted to carbohydrates by day 60. Together, the combination of IAA-producing microbes and Flu-degrading microbes could promote plant growth, facilitate Flu degradation, and change soil microbial functional structure.