Mediated biosynthesis of CdS QDs by EPS from Desulfovibrio desulfuricans sub sp. under carbon source-induced reinforcement

Quorum sensing luxI/R genes enhances cadmium detoxification in Aeromonas by up-regulating EPS production and cadmium resistance genes

The increasing cadmium (Cd) contamination in the environment poses a serious threat to ecosystem health and human safety. This study investigated the roles of quorum sensing (QS) genes luxI/R, key components of the QS system, in the Cd accumulation and detoxification in Aeromonas. Pan-genome analysis showed that luxI/R and Cd resistance genes were highly conserved in Aeromonas species. Strains of luxI/R knockout, complementation and overexpression were constructed via homologous recombination. The luxI/R deletion significantly reduced Cd removal by up to 32 %, decreased extracellular protein (18-36 %) and polysaccharide (19-33 %) contents, whereas luxI/R overexpression enhanced Cd removal capacity by 11 %. Transcriptomic and metabolomic analyses further revealed coordinated changes. In the ΔluxI/R strain, genes involved in assimilatory sulfate reduction and arginine biosynthesis were downregulated, accompanied by reduced levels of glycerophospholipid, vitamin, and cytochrome P450-related metabolites. In contrast, luxI/R overexpression upregulated arginine synthesis (2.0-3.5 fold) and sulfate assimilation (1.4-2.4 fold) genes, with corresponding increases of metabolites. Together these findings demonstrate that luxI/R genes may play a crucial role in regulation of EPS production and Cd resistance gene expression, thus enhancing our understanding of microbial Cd detoxification mechanisms.

Long-term effects of food waste on erosion resistance and production of methane and sulfide in sewer sediments: New insights into extracellular polymeric substances and genetic response mechanisms

Discharge of food waste (FW) into sewer systems causes environmental issues, such as sewer blockage and odour problems. This study investigated the long-term effects of FW addition on sediment properties, microbial communities, and metabolic pathways using laboratory-scale reactors for 160-day incubation. The addition of 2 g/L FW increased the critical erosion shear stress of sediments by 40.63% and reduced their self-cleaning capacity by 39.46%. This was attributed to the fact that FW discharge increased extracellular polymeric substances (EPS) in sediments by 82.94%, especially aromatic protein with high hydrophobicity and high content of intermolecular hydrogen bonds, which was supported by the increased genes encoding aminoacyl-tRNA biosynthesis. The denser biofilm on the sediment surface hindered oxygen transfer to deeper sediment zones, and lowered oxidation-reduction potential below -400 mV. Microbial and metagenomic analysis revealed an enrichment of methanogenic archaea (e.g., Methanothrix) and sulfate-reducing bacteria (e.g., Desulforhabdus), along with increased genes for dissimilatory sulfate reduction and methanogenesis pathways of acetate and CO2/H2. These microbial and metabolic shifts led to a 95.49% and 34.99% increase methane and sulfide production in the FW-2 group. Overall, the negative effects of FW discharge into sewers emphasizes the need for more rational policies to manage this issue.

A one-step route for the conversion of Cd waste into CdS quantum dots by Acidithiobacillus sp. via unique biosynthesis pathways

Microorganisms serve as biological factories for the synthesis of nanomaterials such as CdS quantum dots. Based on the uniqueness of Acidithiobacillus sp., a one-step route was explored to directly convert cadmium waste into CdS QDs using these bacteria. First, an exhaustive study was conducted to reveal the specific pathways involved in the biosynthesis of CdS QDs. The widely known homologous enzyme, cysteine desulfhydrase, which catalyzes the synthesis of CdS QDs from a cysteine substrate, is also present in Acidithiobacillus sp. and is referred to as the OSH enzyme. The structure of the OSH enzyme was determined through X-ray crystallography. Moreover, we identified two new pathways. One involved the SQR enzyme in Acidithiobacillus sp., which catalyzed the formation of sulfur globules and subsequently catalyzed further reactions with GSH to release H2S; subsequently, a CdS QD biosynthesis pathway was successfully constructed. The other pathway involved extracellular polyphosphate, a bacterial metabolic product, which with the addition of GSH and Cd2+, resulted in the formation of water-soluble fluorescent CdS QDs in the supernatant. Based on the above-described mechanism, after the bioleaching of Cd2+ from cadmium waste by Acidithiobacillus sp., CdS QDs were directly obtained from the bacterial culture supernatants. This work provides important insights into cleaner production and cadmium bioremediation with potential industrial applications.

Simultaneous removal of nitrate, manganese, zinc, and bisphenol a by manganese redox cycling system: Performance and mechanism

The manganese(Mn) redox cycling system in this work was created by combining Mn(IV)-reducing bacteria MFG10 with Mn(II)-oxidizing bacteria HY129. The biomanganese oxides (BMO) generated by strain HY129 were transformed by strain MFG10 to Mn(II), finishing the Mn redox cycling, in which nitrate (NO3--N) was converted to nitrite, which was further reduced to nitrogen gas. The system could achieve 85.7 % and 98.8 % elimination efficiencies of Mn(ⅠⅠ) and NO3--N, respectively, at Mn(ⅠⅠ) = 20.0 mg/L, C/N = 2.0, pH = 6.5, and NO3--N = 16.0 mg/L. The removal of bisphenol A (BPA) and zinc (Zn(II)) at 36 h reached 91.7 % and 89.7 % under the optimal condition, respectively. Furthermore, the Mn redox cycling system can reinforce the metabolic activity and electron transfer activity of microorganisms. The findings showed that the adsorption by bioprecipitation throughout the Mn cycling was responsible for the elimination of Zn(II) and BPA.

Metal organic framework-derived CuO/Cu2O polyhedron-CdS quantum dots double Z-scheme heterostructure for cathodic photoelectrochemical detection of Hg2+ in food and environment

This study employed an innovative copper oxide/cuprous oxide (CuO/Cu2O) polyhedron‑cadmium sulphide quantum dots (CdS QDs) double Z-scheme heterostructure as a matrix for the cathodic PEC determination of mercury ions (Hg2+). First, the CuO/Cu2O polyhedral composite was prepared by calcining a copper-based metal organic framework (Cu-MOF). Subsequently, the amino-modified CuO/Cu2O was integrated with mercaptopropionic acid (MPA)-capped CdS QDs to form a CuO/Cu2O polyhedron-CdS QDs double Z-scheme heterostructure, producing a strong cathodic photocurrent. Importantly, this heterostructure exhibited a specifically reduced photocurrent for Hg2+ when using CdS QDs as Hg2+-recognition probe. This was attributed to the extreme destruction of the double Z-scheme heterostructure and the in situ formation of the CuO/Cu2O-CdS/HgS heterostructure. Besides, p-type HgS competed with the matrix for electron acceptors, further decreasing the photocurrent. Consequently, Hg2+ was sensitively assayed, with a low detection limit (0.11 pM). The as-prepared PEC sensor was also used to analyse Hg2+ in food and the environment.

The important role of EPS in mediated biosynthesis of CdS QDs: Comparative study of EPS-intact and EPS-free

In this study, we investigated the adsorption of Cd(II) and the biosynthesis of CdS quantum dots (QDs) mediated by cells of sulfate-reducing bacteria before and after the removal of EPS to determine whether EPS or the cell wall plays a major role. Potentiometric titration revealed that the concentration of proton-active binding sites on cells with EPS (EPS-intact) was notably higher than that on cells without EPS (EPS-free) and that the sites were predominantly carboxyl, phosphoryl, hydroxyl, and amine groups. The protein content in EPS-intact cells was higher, and thus the Cd(II) adsorption capacity was stronger. The CdS QDs biosynthesized using EPS-intact possessed better properties, including uniform size distribution, good crystallinity, small particle size, high fluorescence, and strong antimicrobial activity, and the yields were significantly higher than those of EPS-free by a factor of about 1.5-3.7. Further studies revealed that alkaline amino acids in EPS play a major role and serve as templates in the biosynthesis of QDs, whereas they were rarely detected in the cell wall. This study emphasizes the important role of EPS in the bacterial binding of metals and efficient recycling of hazardous waste in water.

Comprehensive comparison of integrated fixed-film activated sludge (IFAS) and AAO activated sludge methods: Influence of different operational parameters

Due to limited land availability in municipal wastewater treatment plants, integrated fixed-film activated sludge (IFAS) technology offers significant advantages in improving nitrogen removal performance and treatment capacity. In this study, two systems, IFAS and Anaerobic-Anoxic-Oxic Activated sludge process (AAO), were compared by adjusting parameters such as hydraulic retention time (HRT), nitrifying solution recycle ratio, sludge recycle ratio, and dissolved oxygen (DO). The objective was to investigate pollutant removal capacity and differences in microbial community composition between the two systems. The study showed that, at an HRT of 12 h, the IFAS system exhibited an average increase of 5.76%, 8.85%, and 12.79% in COD, NH4+-N, and TN removal efficiency respectively, compared to the AAO system at an HRT of 16 h. The TP concentration in the IFAS system reached 0.82 mg/L without the use of additives. The IFAS system demonstrated superior effluent results under lower operating conditions of HRT, nitrification solution recycle ratio, and DO. The 16S rDNA analysis revealed higher abundance of denitrification-related associated flora, including Proteobacteria, Bacteroidetes, and Planctomycetota, in the IFAS system compared to the AAO system. Similarities were observed between microorganisms attached to the media and activated sludge in the anaerobic, anoxic, and oxic tanks. q-PCR analysis indicated that the incorporation of filler material in the IFAS system resulted in similar abundance of nitrifying bacteria genes on the biofilm as in the oxic tank. Additionally, denitrifying genes showed higher levels due to aeration scouring and the presence of alternating aerobic-anaerobic environments on the biofilm surface, enhancing nitrogen removal efficiency.