Petroleum contamination and bioaugmentation in bacterial rhizosphere communities from Avicennia schaueriana

Synergistic PAH biodegradation by a mixed bacterial consortium: based on a multi-substrate enrichment approach

Polycyclic aromatic hydrocarbon (PAH) contamination in the environment involves multiple PAHs and various intermediates produced during the microbial metabolic process. A multi-substrate enrichment approach was proposed to develop a mixed bacterial community (MBC) from the activated sludge of a coking wastewater plant. The degradation performance of MBC was evaluated under different initial concentrations of PAHs (25-200 mg/L), temperature (20-35 °C), pH (5.0-9.0), salinity (0-10 g/L NaCl), and coexisting substrates (catechol, salicylic acid, and phthalic acid). The results showed that the degradation rates of phenanthrene and pyrene in all treatments were up to (99 ± 0.71)% and (99 ± 0.90)% after incubation of 5 days, respectively, indicating excellent biodegradation ability of PAHs by MBC. Furthermore, 16S rRNA gene amplicon sequencing analysis revealed that Pseudomonas was dominant, while Burkholderia had the largest proportion in acidic (pH = 5.0) and saline (10 g/L NaCl) environments. However, the proportion of dominant bacteria in MBC was markedly affected by intermediate metabolites. It was shown that MBC had a higher degradation rate of PAHs in the coexisting matrix due to the timely clearance of intermediates reducing the metabolic burden. Overall, our study provided valuable information to help design an effective strategy for the bioremediation of PAHs in complex environments.

Rhizoremediation as a green technology for the remediation of petroleum hydrocarbon-contaminated soils

Rhizoremediation is increasingly becoming a green and sustainable alternative to physico-chemical methods for remediation of contaminated environments through the utilization of symbiotic relationship between plants and their associated soil microorganisms in the root zone. The overall efficiency can be enhanced by identifying suitable plant-microbe combinations for specific contaminants and supporting the process with the application of appropriate soil amendments. This approach not only involves promoting the existing activity of plants and soil microbes, but also introduces an adequate number of microorganisms with specific catabolic activity. Here, we reviewed recent literature on the main mechanisms and key factors in the rhizoremediation process with a particular focus on soils contaminated with total petroleum hydrocarbon (TPH). We then discuss the potential of different soil amendments to accelerate the remediation efficiency based on biostimulation and bioaugmentation processes. Notwithstanding some successes in well-controlled environments, rhizoremediation of TPH under field conditions is still not widespread and considered less attractive than physico-chemical methods. We catalogued the major pitfalls of this remediation approach at the field scale in TPH-contaminated sites and, provide some applicable situations for the future successful use of in situ rhizoremediation of TPH-contaminated soils.