Superior performance and mechanism of chlorobenzene degradation by a novel bacterium

Bioanode boosts efficacy of chlorobenzenes-powered microbial fuel cell: Performance, kinetics, and mechanism

Microbial fuel cell (MFC) is a promising device for water decontamination and energy generation. However, the correlation between power generation and pollutant degradation has not been clarified. Herein, a ruthenium-activated carbon (Ru-AC) bioanode was constructed for chlorobenzenes (CBs) treatment. The pollutant tolerance was improved by Ru-AC anode, and the minimum removal efficiencies of CB and ortho-dichlorobenzene (o-DCB) reached 75.1 % and 69.3 %, respectively, which were considerably higher than those of other MFCs (16.3 %-39.7 %). Correspondingly, the maximum output voltage reached 360.7 mV for the Ru-AC anode, whereas the values obtained from others reached 45.2-149.6 mV. Interaction models were introduced to quantify the relationship between power generation and pollutant degradation. The conversion of highly toxic chlorophenols to organic acids could be accelerated by boosting the mass and electron transfer, thereby simultaneously enhancing CBs removal and power generation. This work provided important insights into pollutant-powered MFC development.

Efficient biodegradation of chlorobenzene via monooxygenation pathways by Pandoraea sp. XJJ-1 with high potential for groundwater bioremediation

Chlorobenzene (CB), extensively used in industrial processes, has emerged as a significant contaminant in soil and groundwater. The eco-friendly and cost-effective microbial remediation has been increasingly favored to address this environmental challenge. In this study, a degrading bacterium was isolated from CB-contaminated soil at a pesticide plant, identified as Pandoraea sp. XJJ-1 (CCTCC M 2021057). This strain completely degraded 100 mg·L-1 CB and showed extensive degradability across a range of pH (5.0-9.0), temperature (10-37 °C), and CB concentrations (100-600 mg·L-1). Notably, the degradation efficiency was 85.2% at 15 °C, and the strain could also degrade six other aromatic hydrocarbons, including benzene, toluene, ethylbenzene, and xylene (o-, m-, p-). The metabolic pathway of CB was inferred using ultraperformance liquid chromatography, gas chromatography-mass spectrometry, and genomic analysis. In strain XJJ-1, CB was metabolized to o-chlorophenol and 3-chloroxychol by CB monooxygenase, followed by ortho-cleavage by the action of 3-chlorocatechol 1,2-dioxygenase. Moreover, the presence of the chlorobenzene monooxygenation pathway metabolism in strain XJJ-1 is reported for the first time in Pandoraea. As a bacterium with low-temperature resistance and composite pollutant degradation capacity, strain XJJ-1 has the potential application prospects in the in-situ bioremediation of CB-contaminated sites.

Reduction characteristic of chlorobenzene by a newly isolated Paenarthrobacter ureafaciens LY from a pharmaceutical wastewater treatment plant

A highly efficient chlorobenzene-degrading strain was isolated from the sludge of a sewage treatment plant associated with a pharmaceutical company. The strain exhibited a similarity of over 99.9% with multiple strains of Paenarthrobacter ureafaciens. Therefore, the strain was suggested to be P. ureafaciens LY. This novel strain exhibited a broad spectrum of pollutant degradation capabilities, effectively degrading chlorobenzene and other organic pollutants, such as 1, 2, 4-trichlorobenzene, phenol, and xylene. Moreover, P. ureafaciens LY co-metabolized mixtures of chlorobenzene with 1, 2, 4-trichlorobenzene or phenol. Evaluation of its degradation efficiency showed that it achieved an impressive degradation rate of 94.78% for chlorobenzene within 8 h. The Haldane-Andrews model was used to describe the growth of P. ureafaciens LY under specific pollutants and its concentrations, revealing a maximum specific growth rate (μmax ) of 0.33 h-1 . The isolation and characterization of P. ureafaciens LY, along with its ability to degrade chlorobenzene, provides valuable insights for the development of efficient and eco-friendly approaches to mitigate chlorobenzene contamination. Additionally, investigation of the degradation performance of the strain in the presence of other pollutants offers important information for understanding the complexities of co-metabolism in mixed-pollutant environments.

Metal-organic framework derived bio-anode enhances chlorobenzene removal and electricity generation: Special Ru4+/Ru3+-bridged intracellular electron transfer

Efficient removal of chlorinated organic contaminants using the microbial fuel cell (MFC) provides a promising strategy to alleviate water pollution and energy crisis. However, bio-degradation is challenged by poor biofilm formation and sluggish intracellular electron transfer, causing unsatisfactory electricity generation. To address those problems, a metal-organic framework derivative, Ru-porous TiO2 (Ru-PT) bio-anode has been artfully designed herein for chlorobenzene removal. The Ru-PT bio-anode not only formed a compact anodic biofilm due to the large specific surface area of PT, but more importantly, it introduced special pseudocapacitance-enhanced intracellular electron transfer by slowly implanting Ru4+/Ru3+ redox pair into bacteria. Such a Ru4+/Ru3+ implantation was then found to directionally induce the enrichment of a dual-functional genus (degrader & exoelectrogen), Pseudomonas, thereby enhancing the conversion of bio-refractory chlorophenols towards biodegradable carboxylic acids. These features allowed our MFC to have a resilient chlorobenzene removal and accompanied satisfactory electricity generation, with power density, coulombic efficiency, and turnover frequency reaching 662 mW m-2, 8.7%, and 386,622 s-1, which outcompeted those of other MFCs reported. Further, benefiting from the reversible pseudocapacitance, the Ru-PT bio-anode intriguingly functioned as an internal capacitor for electricity storage. This work provided important insights into cost-effective bio-anode development and offered an avenue for engineering MFC.

Boosting o-xylene removal and power generation in an airlift microbial fuel cell system

Microbial fuel cells (MFCs) are widely acknowledged to be a promising eco-friendly abatement technology of pollutants, and are capable of generating electricity. However, the poor mass transfer and reaction rate in MFCs significantly decrease their treatment capacity for contaminants, especially hydrophobic substances. The present work developed a novel MFC integrated with an airlift (ALR) reactor using a polypyrrole modified anode to promote the bioaccessibility of gaseous o-xylene and attachment of microorganisms. The results indicated that the established ALR-MFC system showed excellent elimination capability, with removal efficiency exceeding 84% even at high o-xylene concentration (1600 mg m^-3). The maximum output voltage of 0.549 V and power density of 13.16 mW m^-2 obtained by the Monod-type model were approximately twice and sixfold higher than that of a conventional MFC, respectively. According to the microbial community analysis, the superior performances of the ALR-MFC in terms of o-xylene removal and power generation were mainly ascribed to the enrichment of degrader (i.e. Shinella) and electrochemical active bacteria (i.e. Proteiniphilum). Moreover, the electricity generation of the ALR-MFC did not decrease at a high O₂ concentration, as O₂ was conducive to o-xylene degradation and electron release. The supplication of an external carbon source such as sodium acetate (NaAc) was conducive to increasing output voltage and coulombic efficiency. The electrochemical analysis revealed that released electrons can be transmitted with the action of NADH dehydrogenase to OmcZ, OmcS, and OmcA outer membrane proteins via a direct or indirect pathway, and ended up transferring to the anode directly.

Isolation and Characterization a Novel Catabolic Gene Cluster Involved in Chlorobenzene Degradation in Haloalkaliphilic Alcanivorax sp. HA03

Chlorobenzene (CB) poses a serious risk to human health and the environment, and because of its low degradation rate by microorganisms, it persists in the environment. Some bacterial strains can use CB as growth substrates and their degradative pathways have evolved; very little is known about these pathways and the enzymes for CB degradation in high pH and salinity environments. Alcanivorax sp. HA03 was isolated from the extremely saline and alkaline site. HA03 has the capability to degrade benzene, toluene and chlorobenzene (CB). CB catabolic genes were isolated from HA03, which have a complete gene cluster comprising α and β subunits, ferredoxin and ferredoxin reductase (CBA1A2A3A4), as well as one gene-encoding enzyme for chlorocatechol 1,2-dioxygenase (CC12DOs). Based on the deduced amino acid sequence homology, the gene cluster was thought to be responsible for the upper and lower catabolic pathways of CB degradation. The CBA1A2A3A4 genes probably encoding a chlorobenzene dioxygenase was confirmed by expression during the growth on CB by RT-PCR. Heterologous expression revealed that CBA1A2A3A4 exhibited activity for CB transformation into 3-chlorocatechol, while CC12DOs catalyze 3-chlorocatechol, transforming it into 2-chloromucounate. SDS-PAGE analysis indicated that the sizes of CbA1 and (CC12DOs) gene products were 51.8, 27.5 kDa, respectively. Thus, Alcanivorax sp. HA03 constitutes the first bacterial strain described in the metabolic pathway of CB degradation under high pH and salinity conditions. This finding may have obvious potential for the bioremediation of CB in both highly saline and alkaline contaminated sites.

External potential regulated biocathode for enhanced removal of gaseous chlorobenzene in bioelectrchemical system

Microbial electrolysis cell (MEC) with a biocathode could provide extra reaction driving force for gaseous chlorobenzene (CB) removal. In this work, external potentials (-0.1 to -0.7 V vs. SHE) were applied to regulate the biocathodic activity. Results showed -0.3 V was the optimum potential, while the removal efficiency, dechlorination efficiency and Coulombic efficiency achieved 94%, 65%, and 89%, respectively. Electrochemical stimulation enriched dechlorination microorganisms (Achromobacter and Gordonia), and significantly improved CB mineralization efficiency, which was twice higher than that without additional potential at 300 mg m^-3 inlet concentration. Furthermore, electron transfer between biocathode and microorganisms was mainly through direct electron transfer (DET). A new integrated redox pathway for CB anaerobic degradation was proposed, in which CB was sequentially converted into 2-chlorophenol and 3-chlorocatechol, then dechlorinated to catechol, and finally mineralized into CO₂. Overall, this work provided an insight into gaseous CB bioelectrochemical degradation through the potential regulation.