Determination of phenol biodegradation pathways in three psychrotolerant yeasts, Candida subhashii A011, Candida oregonensis B021 and Schizoblastosporion starkeyi-henricii L012, isolated from Rucianka peatland

Collaboration of bacterial consortia for biodegradation of high concentration phenol and potential application of machine learning

Mixed culture of microorganisms is an effective method to remove high concentration of phenol in wastewater. At present, it is still a challenge for microorganisms to remove high-concentration phenol from wastewater. In this study, a phenol-degrading consortium was isolated, which could rapidly degrade 1800 mg/L phenol within 30 h, and the highest phenol degradation concentration was 2000 mg/L. Further exploration of how microbial consortium cooperates to promote phenol biodegradation was studied: the core bacteria of the microbial consortium was relatively stable during phenol degradation; the bacteria could improve the adaptability to environment and metabolic ability of phenol, by producing more surfactants and betaine, thereby improving the degradation rate. The determination coefficient (R2) in the machine learning model showed that the back propagation artificial neural network (BP-ANN) can predict the biodegradation of phenol under different conditions, saving time and economic costs. This study explains how microbial consortium cooperates to degrade phenol from the aspects of microbial consortium composition and metabolic analysis, which provides a theoretical basis for mixed culture microorganisms to degrade pollutants.

Can xenobiotics support the growth of Mn(II)-oxidizing bacteria (MnOB)? A case of phenol-utilizing bacteria Pseudomonas sp. AN-1

Biogenic manganese oxides (BioMnOx) produced by Mn(II)-oxidizing bacteria (MnOB) have garnered considerable attention for their exceptional adsorption and oxidation capabilities. However, previous studies have predominantly focused on the role of BioMnOx, neglecting substantial investigation into MnOB themselves. Meanwhile, whether the xenobiotics could support the growth of MnOB as the sole carbon source remains uncertain. In this study, we isolated a strain termed Pseudomonas sp. AN-1, capable of utilizing phenol as the sole carbon source. The degradation of phenol took precedence over the accumulation of BioMnOx. In the presence of 100 mg L-1 phenol and 100 µM Mn(II), phenol was entirely degraded within 20 h, while Mn(II) was completely oxidized within 30 h. However, at the higher phenol concentration (500 mg L-1), phenol degradation reduced to 32% and Mn(II) oxidation did not appear to occur. TOC determination confirmed the ability of strain AN-1 to mineralize phenol. Based on the genomic and proteomics studies, the Mn(II) oxidation and phenol mineralization mechanism of strain AN-1 was further confirmed. Proteome analysis revealed down-regulation of proteins associated with Mn(II) oxidation, including MnxG and McoA, with increasing phenol concentration. Notably, this study observed for the first time that the expression of Mn(II) oxidation proteins is modulated by the concentration of carbon sources. This work provides new insight into the interaction between xenobiotics and MnOB, thus revealing the complexity of biogeochemical cycles of Mn and C.

Enhanced biodegradation of phenol by microbial collaboration: Resistance, metabolite utilization, and pH stabilization

Mixed culture of microorganisms is an effective method to remove high concentration of phenol from wastewater. Currently, the mechanism of how microorganisms collaborate to enhance the biodegradation of phenol is still a challenge. In this study, the isolated Bacillus subtilis ZWB1 and Bacillus velezensis ZWB2 were co-cultured to enhance phenol biodegradation, and the mechanism of microbial collaboration was further explored. The co-culture of strains could significantly increase the rate (16.7 mg/L·h, 1000 mg/L) and concentration of phenol degradation (1500 mg/L), comparing with mono-culture of ZWB1 (4.2 mg/L·h, 150 mg/L) and ZWB2 (6.9 mg/L·h, 1000 mg/L), among which the highest degraded concentration of phenol for ZWB1 and ZWB2 was 150 and 1000 mg/L. Further, the mechanism of microbial collaboration to enhance phenol biodegradation was raised: the decrease of antioxidant enzymes, and increase of degrading enzymes and surfactants on content after co-culture, assisted the microorganisms in withstanding phenol; Bacillus subtilis ZWB1 used the metabolites of Bacillus velezensis ZWB2 to promote its growth, and further to degrade phenol rapidly; Bacillus subtilis ZWB1 alleviated the damage, which resulted from the pH drop (5.8) of the fermentation broth during phenol degradation that inhibited the growth and degraded ability of Bacillus velezensis ZWB2, making the pH of fermentation broth stable at 7. Metabolic analysis showed that co-culture of strains could produce more alkaline and buffering compounds and pairs, to stabilize pH and reduce the toxicity of acidity on ZWB2, thus increasing the degradation rate. This study explains the mechanism of microbial collaboration on phenol biodegradation from multiple perspectives, especially pH stabilization, which provides a theoretical basis for the degradation of pollutants by co-culture microorganisms.

Elucidated potential of immobilized Janibacter sp. for saline wastewater phenol removal

Phenolic compounds are commonly found in industrial effluents and can be hazardous to organisms even at low concentrations. Over the years, researchers have demonstrated that bioremediation is a cost-effective and environmentally friendly alternative to physicochemical approaches used to remove phenol. The aim of this study was to investigate the removal of phenol from saline wastewaters by a halotolerant strain of the genus Janibacter. For this purpose, bacterial cells were immobilized on different supports, from which mica and zeolite were ultimately chosen due to their higher removal efficiency. The wet weight of immobilized cells per 1 g of mica and zeolite was 0.51 and 0.48 g, respectively. Free cells consumed 100 mg/L of phenol in 88 h, while immobilized cells used it in 40 h. Immobilized cells revealed a higher thermostability and could operate over a wider pH range and salinity. Unlike free cells, immobilized cells could remove 700 mg/L of phenol and could be reused for at least nine cycles. Interestingly the phenol removal efficiency of zeolite-immobilized cells remained unchanged after 4 months of storage at 4 and - 20 °C, which could be of great advantage for industrial applications. Complete destruction of phenol was observed through the meta pathway comprising phenol hydroxylase and catechol 2,3-dioxygenase enzymes. KEY POINTS: • Mica- and zeolite-immobilized cells were able to consume high concentrations of phenol. • Cells immobilized on mica and zeolite had considerable operational and storage stability. • Immobilized cells could be a good candidate for phenol removal in saline environments.

Relation of xylitol formation and lignocellulose degradation in yeast

One of the critical steps of the biotechnological production of xylitol from lignocellulosic biomass is the deconstruction of the plant cell wall. This step is crucial to the bioprocess once the solubilization of xylose from hemicellulose is allowed, which can be easily converted to xylitol by pentose-assimilating yeasts in a microaerobic environment. However, lignocellulosic toxic compounds formed/released during plant cell wall pretreatment, such as aliphatic acids, furans, and phenolic compounds, inhibit xylitol production during fermentation, reducing the fermentative performance of yeasts and impairing the bioprocess productivity. Although the toxicity of lignocellulosic inhibitors is one of the biggest bottlenecks of the biotechnological production of xylitol, most of the studies focus on how much xylitol production is inhibited but not how and where cells are affected. Understanding this mechanism is important in order to develop strategies to overcome lignocellulosic inhibitor toxicity. In this mini-review, we addressed how these inhibitors affect both yeast physiology and metabolism and consequently xylose-to-xylitol bioconversion. In addition, this work also addresses about cellular adaptation, one of the most relevant strategies to overcome lignocellulosic inhibitors toxicity, once it allows the development of robust and tolerant strains, contributing to the improvement of the microbial performance against hemicellulosic hydrolysates toxicity. KEY POINTS: • Impact of lignocellulosic inhibitors on the xylitol production by yeasts • Physiological and metabolic alterations provoked by lignocellulosic inhibitors • Cell adaptation as an efficient strategy to improve yeast's robustness.

Fungal co-culture improves the biodegradation of hydrophobic VOCs gas mixtures in conventional biofilters and biotrickling filters

The present study systematically evaluated the potential of Candida subhashii, Fusarium solani and their consortium for the abatement of n-hexane, trichloroethylene (TCE), toluene and α-pinene in biofilters (BFs) and biotrickling filters (BTFs). Three 3.2 L BFs packed with polyurethane foam and operated at a gas residence time of 77 s with an air mixture of hydrophobic volatile organic compounds (VOCs) were inoculated with C. subhashii, F. solani and a combination of thereof. The systems were also operated under a BTF configuration with a liquid recirculating rate of 2.5 L h^-1. Steady state elimination capacities (ECs) of total VOCs of 17.4 ± 0.7 g m^-3 h^-1 for C. subhashii, 21.2 ± 0.8 g m^-3 h^-1 for F. solani and 24.4 ± 1.4 g m^-3 h^-1 for their consortium were recorded in BFs, which increased up to 27.2 ± 1.6 g m^-3 h^-1, 29.2 ± 1.9 g m^-3 h^-1, 37.7 ± 3.3 g m^-3 h^-1 in BTFs. BTFs supported a superior biodegradation performance compared to BF, regardless of the VOCs. Moreover, a more effective VOC biodegradation was observed when C. subhashii and F. solani were grown as a consortium. The microbial analysis conducted revealed that the fungi initially introduced in each BF represented the dominant species by the end of the experiment, with C. subhashii gradually overcoming F. solani in the system inoculated with the fungal consortium.

Thermally enhanced bioremediation: A review of the fundamentals and applications in soil and groundwater remediation

Thermally enhanced bioremediation (TEB), a new concept proposed in recent years, explores the combination of thermal treatment and bioremediation to address the challenges of the low efficiency and long duration of bioremediation. This study presented a comprehensive review regarding the fundamentals of TEB and its applications in soil and groundwater remediation. The temperature effects on the bioremediation of contaminants were systematically reviewed. The thermal effects on the physical, chemical and biological characteristics of soil, and the corresponding changes of contaminants bioavailability and microbial metabolic activities were summarized. Specifically, the increase in temperature within a suitable range can proliferate enzymes enrichment, extracellular polysaccharides and biosurfactants production, and further enhancing bioremediation. Furthermore, a systematic evaluation of TEB applications by utilizing traditional in situ heating technologies, as well as renewable energy (e.g., stored aquifer thermal energy and solar energy), was provided. Additionally, TEB has been applied as a biological polishing technology post thermal treatment, which can be a cost-effective method to address the contaminants rebounds in groundwater remediation. However, there are still various challenges to be addressed in TEB, and future research perspectives to further improve the basic understanding and applications of TEB for the remediation of contaminated soil and groundwater are presented.

Simultaneous biodegradation of phenolics and petroleum hydrocarbons from semi-coking wastewater: Construction of bacterial consortium and their metabolic division of labor

Phenols and petroleum hydrocarbons were the main contributors to COD in semi-coking wastewater, and their removal was urgent and worthwhile. The microbial strains were selected to construct microbial community for the wastewater treatment. The concentration of phenols was decreased from 2450 ± 1.2 mg/L to 200 ± 0.9 mg/L, and the removal rate of petroleum hydrocarbons was up to 97.08 ± 0.09 % by microorganisms. After phenolic compounds with high toxicity were removed by bioaugmentation, the treated semi-coking wastewater was more biodegradable, and its water quality has been significantly improved. Through GC-MS and high-through sequencing technology, the metabolic division of labor in degradation of phenols, ring-cleavage of aromatic compounds, mineralization of metabolites was further revealed. The microbial community consisting of Pseudomonas stutzeri N2 and Rhodococcus qingshengii FF could effectively and simultaneously remove phenols and petroleum hydrocarbons, and these two strains possess great potential of being applied in aerobic biological treatment process of large-scale semi-coking wastewater.

Bacillus thuringiensis A1 improve phenol tolerance and phytoextraction by Acorus calamus L

Phenol, as a very toxic pollutant, exists widely in rivers in China. To explore the effect of bacterial augmentation on phytoremediation of phenol by Acorus calamus L., some plant growth and physiological parameters and percent removal of phenol were determined in hydroponics containing phenol with addition of Bacillus thuringiensis A1. The A. calamus L. and B. thuringiensis A1 consortium increased the growth rate of plant height, chlorophyll content, the activity of superoxide dismutase (SOD) and peroxidase (POD) in A. calamus L. 10.00-36.54%, 0.62 - 22.15%, 3.94 - 11.25% and 1.37-10.50% respectively compared with single plant treatments at same phenol concentrations. However, the addition of B. thuringiensis A1 decreased the content of malondialdehyde (MDA) and relative electrical conductivity (REC) in A. calamus L. 12.99-23.66% and 8.38-29.98% respectively compared with single plant treatments. The removal efficiency of phenol (increased from 1.56% to 13.78%) by the A. calamus L. and B. thuringiensis A1 consortium was higher than the removal efficiency of phenol of the independent A. calamus L. system. In conclusion, the addition of B. thuringiensis A1 alleviated phenol stress to A. calamus L and enhanced phenol removal due to phenol removal by bacterial augmentation.Novelty statementThe addition of B. thuringiensis A1 alleviated phenol stress to A. calamus L. and enhanced phenol removal due to phenol removal by bacterial augmentation.

Enhanced degradation of phenol by a novel biomaterial through the immobilization of bacteria on cationic straw

As phenol possesses a threat to human health, there is a great demand to search for fast and efficient methods for it to be discharged. In this study, a novel biomaterial was prepared by the immobilization of bacteria on a cationic straw carrier, and the remediation ability of the biomaterial on phenol-containing wastewater was investigated. The free bacteria could degrade 1,000 mg/L phenol within 240 h, while the prepared biomaterial was 192 h, shortening by 48 h that of free bacteria. In addition, the degradation tolerance of biomaterial increased from 1,000 mg/L to 1,200 mg/L than the free bacteria, within 216 h, which shortened by 24 h the degradation time of 1,000 mg/L phenol by free bacteria (240 h). Further, under different pH conditions, the degradation efficiency of phenol by prepared biomaterial was much higher than that of free bacteria. Especially for the lower pH 5, the degradation efficiency of biomaterial was nearly twice that of the free bacteria. This investigation demonstrates that this biomaterial has great potential in the field of remediation of organic pollution.

Biodegradation of phenol by a halotolerant versatile yeast Candida tropicalis SDP-1 in wastewater and soil under high salinity conditions

In this study, a novel halotolerant phenol-degrading yeast strain, SDP-1, was isolated from a coastal soil in Jiangsu, China, and identified as Candida tropicalis by morphology and rRNA internal transcribed space region sequence analysis. Strain SDP-1 can efficiently remove phenol at wide ranges of pH (3.0-9.0), temperature (20-40 °C), and NaCl (0-5%, w/v), as well as the tolerance of Mn²⁺, Zn²⁺ and Cr³⁺ in aquatic phase. It also utilized multiple phenol derivatives and aromatic hydrocarbons as sole carbon source and energy for growth. Free cells of SDP-1 were able to degrade the maximum phenol concentration of 1800 mg/L within 56 h under the optimum culture conditions of 10% inoculum volume, pH 8.0, 35 °C and 200 rpm agitation speed. Meanwhile, SDP-1 was immobilized on sodium alginate, and the capability of efficiently phenol degradation of free cells and immobilized SDP-1 were evaluated. Shortened degradation time and long-term utilization and recycling for immobilized SDP-1 was achieved compared to free cells. The 1200 mg/L of phenol under 5% NaCl stress could be completely degraded within 40 h by immobilized cells. In actual industrial coking wastewater, immobilized cells were able to completely remove 383 mg/L phenol within 20 h, and the corresponding chemical oxygen demand (COD) value was decreased by 50.38%. Besides, in phenol-contained salinity soil (3% NaCl), 100% of phenol (500 and 1000 mg/kg) removal efficiency was achieved by immobilized SDP-1 within 12 and 26 days, respectively. Our study suggested that versatile yeast Candida tropicalis SDP-1 could be potentially used for enhanced treatment of phenol-contaminated wastewater and soil under hypersaline or no-salt environmental conditions.