The pathways by which the marine diatom Thalassiosira sp. OUC2 biodegrades p-xylene, combined with a mechanistic analysis at the proteomic level

Integration of Moving Bed Biofilm Reactor (MBBR) and algal PhotoBioReactors (aPBR) for achieving carbon neutrality in wastewater treatment

Carbon neutrality is a primary goal for wastewater treatment plants (WWTPs), as they are responsible for significant greenhouse gas (GHG) emissions as well as unpleasant odour emissions. The paper shows a new modular biotechnology that enables simultaneous treatment of gaseous emissions and biofixation of CO2. A comparative assessment of system performances in removing target pollutants (toluene, p-xylene and hydrogen sulphide) was implemented. Results showed that the highest removal efficiency (RE) was recorded for the toluene, equaling 99.9 ± 0.1 %, for an inlet load (IL) of 9.91 ± 3.44 g m-3 d-1. During the experimental tests regarding hydrogen sulphide removal, the system recorded the highest CO2 assimilation, equal to -3.03 ± 0.93 g m-3 d-1. However, this assimilation rate did not correspond to the maximum volumetric biomass productivity (MVBP), equal to 1.3 g L-1 d-1, recorded with toluene treatment, with a maximum lipid productivity (MLP) of 450 mg L-1 d-1. The results demonstrated the complete adaptability of the investigated system, which can help to fill the gaps in the current technological landscape, providing an innovative biotechnology that can be directly implemented and environmentally sustainable.

Effects of environmental concentrations of sulfamethoxazole on Skeletonema costatum and Phaeodactylum tricornutum: Insights into growth, oxidative stress, biochemical components, ultrastructure, and transcriptome

This study aimed to assess the ecological risks posed by sulfamethoxazole (SMX) at environmentally relevant concentrations. Specifically, its effects on the growth and biochemical components (total protein, total lipid, and total carbohydrate) of two marine microalgae species, namely Skeletonema costatum (S. costatum) and Phaeodactylum tricornutum (P. tricornutum), were investigated. Our findings revealed that concentrations of SMX below 150 ng/L stimulated the growth of both microalgae. Conversely, at higher concentrations, SMX inhibited their growth while promoting the synthesis of photosynthetic pigments, total protein, total lipid, and total carbohydrate (P < 0.05). Transmission electron microscope (TEM) observations demonstrated significant alterations in the ultrastructure of algal cells exposed to SMX, including nuclear marginalization, increased chloroplast volume, and heightened vacuolation. In addition, when SMX was lower than 250 ng/L, there was no oxidative damage in two microalgae cells. However, when SMX was higher than 250 ng/L, the antioxidant defense system of algal cells was activated to varying degrees, and the level of malondialdehyde (MDA) increased, indicating that algae cells were damaged by oxidation. From the molecular level, environmental concentration of SMX can induce microalgae cells to produce more energy substances, but there are almost no other adverse effects, indicating that the low level of SMX at the actual exposure level was unlikely to threaten P. tricornutum, but a higher concentration can significantly reduce its genetic products, which can affect the changes of its cell structure and damage P. tricornutum to some extent. Therefore, environmental concentration of SMX still has certain potential risks to microalgae. These outcomes improved current understanding of the potential ecological risks associated with SMX in marine environments.

Microalgal multiomics-based approaches in bioremediation of hazardous contaminants

The enhanced industrial growth and higher living standards owing to the incessant population growth have caused heightened production of various chemicals in different manufacturing sectors globally, resulting in pollution of aquatic systems and soil with hazardous chemical contaminants. The bioremediation of such hazardous pollutants through microalgal processes is a viable and sustainable approach. Accomplishing microalgal-based bioremediation of polluted wastewater requires a comprehensive understanding of microalgal metabolic and physiological dynamics. Microalgae-bacterial consortia have emerged as a sustainable agent for synergistic bioremediation and metabolite production. Effective bioremediation involves proper consortium functioning and dynamics. The present review highlights the mechanistic processes employed through microalgae in reducing contaminants present in wastewater. It discusses the multi-omics approaches and their advantages in understanding the biological processes, monitoring, and dynamics among the partners in consortium through metagenomics. Transcriptomics, proteomics, and metabolomics enable an understanding of microalgal cell response toward the contaminants in the wastewater. Finally, the challenges and future research endeavors are summarised to provide an outlook on microalgae-based bioremediation.

Efficiency, mechanism, influencing factors, and integrated technology of biodegradation for aromatic compounds by microalgae: A review

Aromatic compounds have received widespread attention because of their threat to ecosystem and human health. However, traditional physical and chemical methods are criticized due to secondary pollution and high cost. As a result of ecological security and the ability of carbon sequestration, biodegradation approach based on microalgae has emerged as a promising alternative treatment for aromatic pollutants. In light of the current researches, the degradation efficiency of BTEX (benzene, toluene, ethylbenzene, and xylene), polycyclic aromatic hydrocarbons (PAHs), and phenolic compounds by microalgae was reviewed in this study. We summarized the degradation pathways and metabolites of p-xylene, benzo [a]pyrene, fluorene, phenol, bisphenol A, and nonylphenol by microalgae. The influence factors on the degradation of aromatic compounds by microalgae were also discussed. The integrated technologies based on microalgae for degradation of aromatic compounds were reviewed. Finally, this study discussed the limitations and future research needs of the degradation of these compounds by microalgae.

Newly isolated Enterobacter cloacae sp. HN01 and Klebsiella pneumoniae sp. HN02 collaborate with self-secreted biosurfactant to improve solubility and bioavailability for the biodegradation of hydrophobic and toxic gaseous para-xylene

The gas-liquid mass transfer rate of hydrophobic volatile organic compounds (VOCs) is the limiting step in a biological treatment system. The present study aimed to utilize self-producing biosurfactants to enhance the bioavailability of hydrophobic gaseous VOCs. Two novel gram-negative rod-shaped bacteria, Enterobacter cloacae strain HN01 and Klebsiella pneumoniae strain HN02 were successfully isolated from sewage sludge by using blood agar and methylene blue agar plates. The two strains can use para-xylene (PX), a hydrophobic VOC model, as the only carbon source for biosurfactant production. Both strains can produce glycolipid biosurfactants, as confirmed by the emulsification index, Nuclear magnetic resonance, and Fourier transform infrared spectroscopy. Results indicated that PX can be completely decomposed at an initial concentration of 15.50 mg L^-1, pH value of 7.0, and temperature of 30 °C within 36 h. The Yano model is suitable for the prediction of the growth kinetics of strains over the entire PX concentration range. Gas chromatography/mass spectrometry analysis indicated that PX was converted into four and four intermediates in the presence of the strains HN01 and HN02, respectively, and the possible mechanisms were proposed. The results can be used in purifying industrial hydrophobic gaseous VOCs and improving the bioavailability of VOCs with self-produced biosurfactants.

The role of Fe3O4@biochar as electron shuttle in enhancing the biodegradation of gaseous para-xylene by aerobic surfactant secreted strains

To study the role of electron shuttles in accelerating the biodegradation of volatile organic compounds (VOCs) and provide theoretical support for purification of waste gas containing PX, two self-producing biosurfactant strains were used to improve solubility, and the magnetic Fe₃O₄@biochar composites were prepared as electron shuttles to accelerate extracellular electron transfer during the process of para-xylene (PX) biodegradation. The composites were characterized by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The biodegradation time of PX by Enterobacter sp. HN01 and Klebsiella sp. HN02 decreased from 192 h to 12 h and 120 to 12 h, and approximately 93.75% and 90.00% of the removal times were saved after the addition of the composites. Furthermore, the effects of Fe₃O₄@biochar on the bacterial biosurfactant secretion, self-enzyme activity, and bacterial growth inhibition by PX were explored. The electron transport capacity of Fe₃O₄@biochar was 4.583 mmol·e^-/g detected by mediated electrochemical reduction and mediated electrochemical oxidation, and possible electron transport pathways were revealed. The possible products of PX biodegradation by HN01 and HN02 were determined through gas chromatography-mass spectrometry. The molecular structure of PX was deduced through density functional theory calculation to validate the key product. Results indicated that Fe₃O₄@biochar can be used as an electronic shuttle to accelerate extracellular electron transfer and significantly improve VOCs removal rate.

Biodegradation of p-xylene-a comparison of three psychrophilic Pseudomonas strains through the lens of gene expression

p-Xylene is considered a recalcitrant compound despite showing a similar aromatic structure to other BTEXs (benzene, toluene, ethylbenzene, xylene isomers). This study evaluated the p-xylene biodegradation potential of three psychrophilic Pseudomonas strains (Pseudomonas putida S2TR-01, Pseudomonas synxantha S2TR-20, and Pseudomonas azotoformans S2TR-09). The p-xylene metabolism-related catabolic genes (xylM, xylA, and xylE) and the corresponding regulatory genes (xylR and xylS) of the selected strains were investigated. The biodegradation results showed that the P. azotoformans S2TR-09 strain was the only strain that was able to degrade 200 mg/L p-xylene after 60 h at 15 °C. The gene expression study indicated that the xylE (encoding catechol 2,3-dioxygenase) gene represents the bottleneck in p-xylene biodegradation. A lack of xylE expression leads to the accumulation of intermediates and the inhibition of biomass production and complete carbon recovery. The activity of xylene monooxygenase and catechol 2,3-dioxygenase was significantly increased in P. azotoformans S2TR-09 (0.5 and 0.08 U/mg, respectively) in the presence of p-xylene. The expression of the ring cleavage enzyme and its encoding gene (xylE) and activator (xylS) explained the differences in the p-xylene metabolism of the isolated bacteria and can be used as a novel biomarker of efficient p-xylene biodegradation at contaminated sites.

Natural attenuation characteristics and comprehensive toxicity changes of C9 aromatics under simulated marine conditions

Microcosmic experiments were performed under a simulated marine environment to investigate the natural attenuation of C9 aromatics using nine components (propylbenzene, isopropylbenzene, 2-ethyltoluene, 3-ethyltoluene, 4-ethyltoluene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, and indene). This research aims to assess the contribution of biodegradation and abiotic activity to total attenuation of C9 aromatics and ascertain the changes in the comprehensive toxicity of seawater in the natural environment. The process of natural attenuation indicates the agreement with pseudo-first-order kinetics for all nine components in microcosmic experiments. The half-lives of the nine main compounds in C9 aromatics ranged between 0.34 day and 0.44 day under optimal conditions. The experiments showed that the natural attenuation of nine aromatic hydrocarbons mainly occurred via abiotic processes. Seawater samples significantly inhibited the luminescence of P. phosphoreum (the luminescence inhibition ratio reached 100%) at the beginning of the experiment. In addition, the toxicity declined slowly and continued for 25 days. The attenuation kinetics and changes in toxicity could be applied to explore the natural attenuation of C9 aromatics in the marine environment.