Pyridine degradation characteristics of a newly isolated bacterial strain and its application with a novel reactor for the further treatment in pyridine wastewater

Unveiling the hidden impact: How human disturbances threaten aquatic microorganisms in cities

Urban activity emissions have important ecological significance to bacterial communities' spatial and temporal distribution and the mechanism of bacterial community construction. The mechanism of bacterial community construction is the key to community structure and lifestyle, and the influence of this aspect has not been thoroughly studied. This study analyzed the response of bacteria in water and sediment in different seasons to urban activities in Jinsha River. The results showed that the influence of urban activities on bacterial community structure in sediment was greater than that in water. The input of pollution in different regions changed the diversity and abundance of water and sediments bacteria and promoted bacterial community reconstruction to a certain extent. Co-network analysis found that many metal-mediated species are core species within the same module and can be used to mitigate pollution caused by metal or organic pollutants due to interspecific solid interactions. Different potential pollution sources around urban rivers affect the metabolic function of bacteria in aquatic ecosystems and promote the detoxification function of bacteria in different media. The results of this study supplement our understanding of the characteristics of microbial communities in urban river systems and provide clues for understanding the maintenance mechanism of microbial diversity in multi-pollution environments.

Complete genome sequence of Rhodococcus sp. strain PD04, a pyridine-degrading bacterium under hypersaline condition

We report the complete genome sequence of a pyridine-degrading Rhodococcus sp. strain PD04 under 4% salinity environment, isolated from wastewater of coking plant. The genome is 6.07 Mb with 5,767 annotated gene coding sequences.

Regulating microbial redox reactions towards enhanced removal of refractory organic nitrogen from wastewater

Biotechnology for wastewater treatment is mainstream and effective depending upon microbial redox reactions to eliminate diverse contaminants and ensure aquatic ecological health. However, refractory organic nitrogen compounds (RONCs, e.g., nitro-, azo-, amide-, and N-heterocyclic compounds) with complex structures and high toxicity inhibit microbial metabolic activity and limit the transformation of organic nitrogen to inorganic nitrogen. This will eventually result in non-compliance with nitrogen discharge standards. Numerous efforts suggested that applying exogenous electron donors or acceptors, such as solid electrodes (electrostimulation) and limited oxygen (micro-aeration), could potentially regulate microbial redox reactions and catabolic pathways, and facilitate the biotransformation of RONCs. This review provides comprehensive insights into the microbial regulation mechanisms and applications of electrostimulation and micro-aeration strategies to accelerate the biotransformation of RONCs to organic amine (amination) and inorganic ammonia (ammonification), respectively. Furthermore, a promising approach involving in-situ hybrid anaerobic biological units, coupled with electrostimulation and micro-aeration, is proposed towards engineering applications. Finally, employing cutting-edge methods including multi-omics analysis, data science driven machine learning, technology-economic analysis, and life-cycle assessment would contribute to optimizing the process design and engineering implementation. This review offers a fundamental understanding and inspiration for novel research in the enhanced biotechnology towards RONCs elimination.

Effect of microplastics on oxytetracycline trophic transfer: Immune, gut microbiota and antibiotic resistance gene responses

Microplastics and antibiotics are prevalent and emerging pollutants in aquatic ecosystems, but their interactions in aquatic food chains remain largely unexplored. This study investigated the impact of polypropylene microplastics (PP-MPs) on oxytetracycline (OTC) trophic transfer from the shrimp (Neocaridina denticulate) to crucian carp (Carassius auratus) by metagenomic sequencing. The carrier effects of PP-MPs promoted OTC bioaccumulation and trophic transfer, which exacerbated enterocyte vacuolation and hepatocyte eosinophilic necrosis. PP-MPs enhanced the inhibitory effect of OTC on intestinal lysozyme activities and complement C3 levels in shrimp and fish, and hepatic immunoglobulin M levels in fish (p < 0.05). Co-exposure of MPs and OTC markedly increased the abundance of Actinobacteria in shrimp and Firmicutes in fish, which caused disturbances in carbohydrate, amino acid, and energy metabolism. Moreover, OTC exacerbated the enrichment of antibiotic resistance genes (ARGs) in aquatic animals, and PP-MPs significantly increased the diversity and abundance of ARGs and facilitated the trophic transfer of teta and tetm. Our findings disclosed the impacts of PP-MPs on the mechanism of antibiotic toxicity in aquatic food chains and emphasized the importance of gut microbiota for ARGs trophic transfer, which contributed to a deeper understanding of potential risks posed by complex pollutants on aquatic ecosystems.

Novel insights into the co-metabolism of pyridine with different carbon substrates: Performance, metabolism pathway and microbial community

Pyridine is a widely employed nitrogen-containing heterocyclic organic, and the discharge of pyridine wastewater poses substantial environmental challenges due to its recalcitrance and toxicity. Co-metabolic degradation emerged as a promising solution. In this study, readily degradable glucose and the structurally analogous phenol were used as co-metabolic substrates respectively, and the corresponding mechanisms were thoroughly explored. To treat 400 mg/L pyridine, all reactors achieved remarkably high removal efficiencies, surpassing 98.5%. And the co-metabolism reactors had much better pyridine-N removal performance. Batch experiments revealed that glucose supplementation bolstered nitrogen assimilation, thereby promoting the breakdown of pyridine, and resulting in the highest pyridine removal rate and pyridine-N removal efficiency. The high abundance of Saccharibacteria (15.54%) and the enrichment of GLU and glnA substantiated this finding. On the contrary, phenol delayed pyridine oxidation, potentially due to its higher affinity for phenol hydroxylase. Nevertheless, phenol proved valuable as a carbon source for denitrification, augmenting the elimination of pyridine-N. This was underscored by the abundant Thauera (30.77%) and Parcubacteria (7.21%) and the enriched denitrification enzymes (narH, narG, norB, norC, and nosZ, etc.). This study demonstrated that co-metabolic degradation can bolster the simultaneous conversion of pyridine and pyridine-N, and shed light on the underling mechanism.

Carbon quantum dot-induced developmental toxicity in Daphnia magna involves disturbance of symbiotic microorganisms

With the increasing synthesis and application of carbon quantum dots (CQDs), their prevalence as pollution in water environments has increased. However, the toxic effects of CQDs on aquatic organisms are unclear, and their environmental safety must be evaluated. Herein, Daphnia magna was used as a model organism to explore the developmental toxicity of CQDs under a full life-cycle exposure. It was found that the feeding rate and offing number of D. magna decreased with increasing CQD concentration, and the body length of D. magna showed a trend of first increasing and then decreasing. These results indicated that long-term exposure to CQDs has evident toxic effects on D. magna development. Symbiosis analysis showed that the composition of the symbiotic microbial community of D. magna was disturbed by CQDs. The abundance of microorganisms involved in the immune response of D. magna such as Rhodobacter, decreased; those involved in the inflammation such as Gemmobacter, increased; and those involved in the nitrogen cycle, such as Hydrogenophaga and Paracoccus, decreased. When D. magna was subjected to environmental pressure, host-microflora interactive immune regulation was induced. The abundance of probiotics in D. magna, such as Rhodococcus, increased in response to environmental pressure. The results of KEGG function prediction showed that the abundance of symbiotic microorganisms involved in energy absorption and metabolism was affected by CQDs. In addition, the correlation analysis showed that there was a correlation between the changes in the symbiotic microbial community and the damage to D. magna after exposure to CQDs. Thus, it is appealed that as a potential environmental pollutant, CQDs have aquatic environmental risks, and their safe application deserves attention.

Efficient pyridine biodegradation by Stenotrophomonas maltophilia J2: Degradation performance, mechanism, and immobilized application for wastewater

Stenotrophomonas maltophilia J2, a highly efficient pyridine-degrading bacterium, was isolated from the aerobic tank of a pesticide-contaminated wastewater treatment plant. The strain J2 demonstrated an impressive pyridine degradation rate of 98.34% ± 0.49% within 72 h, at a pyridine concentration of 1100 mg·L-1, a temperature of 30 °C, a pH of 8.0, and a NaCl concentration of 0.5%. Notably, two new pyridine metabolic intermediates, 1,3-dihydroxyacetone and butyric acid, were discovered, indicating that J2 may degrade pyridine through two distinct metabolic pathways. Furthermore, the immobilized strain J2 was obtained by immobilizing J2 with biochar derived from the stem of Solidago canadensis L. In the pyridine-contaminated wastewater bioremediation experiment, the immobilized strain J2 was able to remove 2000 mg·L-1 pyridine with a 98.66% ± 0.47% degradation rate in 24 h, which was significantly higher than that of the control group (3.17% ± 1.24%), and remained above 90% in subsequent cycles until the 27th cycle. High-throughput sequencing analysis indicated that the J2 +B group had an elevated relative abundance of bacteria and functional genes that could be associated with the degradation of pyridine. The results offer a foundation for the effective use of immobilized strain in the treatment of recalcitrant pyridine-contaminated wastewater.

Microplastics in feed cause sublethal changes in the intestinal microbiota and a non-specific immune response indicator of the freshwater crayfish Procambarus clarkii (Decapoda: Cambaridae)

Microplastics (MP) are a hazardous pollutant of global concern that threatens aquatic ecosystems and public health. We used the invasive, cosmopolitan, and environmentally versatile red swamp crayfish Procambarus clarkii as a model to study the effects of MP on the intestinal microbiome. Crayfish collected from the environment were compared with specimens exposed to recycled Polyethylene terephthalate (rPET) MP in feed (30%) for 96 h in the laboratory and a control group. We analyzed the 16S rRNA of the intestinal bacteria by PCR-DGGE and high-throughput sequencing. MP exposure caused dysbiosis of the intestinal microbiota, with an increase in Alphaproteobacteria and Actinobacteria. We detected higher abundance of opportunistic genera such as Klebsiella, Acinetobacter, Hydromonas, Pseudomonas, Gemmobacter, and Enterobacter on MP fed organisms. Moreover, MP exposure reduced the abundance of Clostridia and Bateroidetes, which are important for immune system development and pathogen prevention. Furthermore, MP exposure decreased the phenoloxidase (PO) immune response in crayfish. There was a significant difference in the richness of intestinal bacterial communities after consumption of food contaminated with MP, likely increasing the abundance of opportunistic bacteria in the intestinal microbiota. Our results suggest that MP alter the gut microbial composition and impair the health of P. clarkii.

Microbial metabolism regulation on the efficient degradation of aromatic compounds for biochemical treatment process of coal chemical wastewater in pilot scale

At present, the common problems of biochemical treatment systems of coal chemical wastewater were the poor system stability and the difficulty in reaching COD discharge standards. Aromatic compounds were the main contributors to COD value. The effective removal of aromatic compounds was an urgent problem in the biochemical treatment systems of coal chemical wastewater. In this study, the dominant microbial strains that could degrade phenol, quinoline, and phenanthrene were isolated respectively and inoculated into the pilot scale biochemical tank of coal chemical wastewater. The regulation effect and mechanism of microbial metabolism on the efficient degradation of aromatic compounds were studied. The results indicated that the various aromatic compounds were significantly removed under the regulation of microbial metabolism, the removal efficiencies of COD, TOC, phenols, benzenes, N-CHs, and PAHs were increased by about 25%, 20%, 33%, 25%, 42%, and 45%, respectively, and their biotoxicity was also drastically reduced. Moreover, the abundance and diversity of microbial community, and the microbial activity were obviously improved, as well as the various functional strains were selectively enriched, suggesting that the regulation system could resist environmental stresses with high substrate concentration and toxicity, which could lead to more enhanced performance for aromatic compounds removal. In addition, the microbial EPS content was significantly increased, implying the formation of microbial hydrophobic cell surfaces, which could improve the bioavailability of aromatic compounds. Furthermore, the enzymatic activity analysis revealed that the relative abundance and activity of key enzymes were all obviously improved. In conclusion, multiple lines of evidence were provided to clarify the regulation mechanism of microbial metabolism on the efficient degradation of aromatic compounds for biochemical treatment process of coal chemical wastewater in pilot scale. The results laid a good foundation for realizing the harmless treatment of coal chemical wastewater.

Detoxification of typical nitrogenous heterocyclic compound from pharmaceutical wastewater by mixed microbial consortia

Microbial consortia HY3 and JY3 with high degradation efficiency of 2-Diethylamino-4-hydroxy-6-methylpyrimidine (DHMP) were isolated from aerobic and parthenogenic ponds of DHMP-containing pharmaceutical wastewater, respectively. Both consortia were enriched and reached stable degradation performance with a DHMP concentration of 1500 mg L^-1. The DHMP degradation efficiencies of HY3 and JY3 were 95.66% ± 0.24% and 92.16% ± 2.34% under the condition of shaking at 180 r·min^-1 and the temperature of 30 °C for 72 h. And the removal efficiencies of chemical oxygen demand were 89.14% ± 4.78% and 80.30% ± 11.74%, respectively. High-throughput sequencing results indicated that three bacterial phyla of Proteobacteria, Bacteroidetes, and Actinobacteria were dominant in both HY3 and JY3, but their dominances varied. At the genus level, the richness of Unclassified Comamonadaceae (34.23%), Paracoccus (14.75%), and Brevundimonas (13.94%) ranked top three in HY3 whereas Unclassified Comamonadaceae (40.80%), Unclassified Burkholderiales (13.81%) and Delftia (13.11%) were dominant in JY3. The metabolites of DHMP degradation by HY3 and JY3 were analyzed in detail. Two pathways for cleavage of the nitrogenous heterocyclic ring were speculated, one of which was identified for the first time in this study.

Anoxic/oxic treatment without biomass recycle

The Anoxic/Oxic (A/O) process involves recirculating mixed liquor between its A and O tanks so that nitrate produced in the O tank can be used to for denitrification with influent COD in the A tank. Because biomass is recirculated along with nitrate, A/O operation leads to similar microbial communities in the A and O tanks, which may decrease the rates of denitrification and nitrification in each tank. Here, bench-scale experiments simulated this aspect of the A/O process by exchanging biomass between an anoxic flask and an oxic cylinder at exchange ratios of 0%, 20%, 30%, and 50%. Nitrification and denitrification rates were only 40% and 19% for 50% biomass exchange of that for no biomass exchange. Phylogenetic analysis documented that the microbial communities became much more similar with biomass exchange, and the finding was consistent with community composition in a full-scale A/O process in a municipal wastewater treatment plant. A two-stage vertical baffled bioreactor (VBBR) realized efficient total‑nitrogen removal in recirculation without biomass exchange. Average removals of COD and TN were respectively 6% and 22% higher for the two-stage VBBR than the conventional A/O process, but its hydraulic retention time (HRT) was 55% to 70% of the volume of a conventional A/O process treating the same influent wastewater. The VBBR was more efficient because its anoxic biofilm was enriched in denitrifying bacteria, while its oxic biofilm was enriched in nitrifying bacteria. For example, the phylum Chloroflexi was greater in the An-VBBR, while the phylum Proteobacteria was greater in the Ox-VBBR.

Metagenomic analysis explores the interaction of aged microplastics and roxithromycin on gut microbiota and antibiotic resistance genes of Carassius auratus

The aging process changes the physicochemical structure of microplastics and affects environmental behaviors and toxicological effects of coexisting pollutants, thereby posing ecological risks. In this study, the effects of aged polystyrene microplastics alone or in combination with the 100 μg/L roxithromycin (ROX) on intestines of Carassius auratus were investigated. The carrier effect of microplastics was enhanced by aging due to changes in functional groups and surface area, which led to an increase in the bioaccumulation of ROX. The combined exposure of aged microplastics (APS) and ROX caused more inflammatory cell infiltration and cilia defects, and significantly inhibited the activity of amylase and lipase. Metagenomic sequencing revealed that the combined exposure of microplastics and ROX increased the abundance of Gemmobacter, Bosea, Rhizobium, and Shinella and decreased the abundance of Cetobacterium and Akkermansia (p < 0.05). The presence of APS enhanced the selective enrichment of antibiotic resistance genes. What's more, the influence of microplastics and antibiotics on gut microbiota was closely related to carbohydrate metabolism and amino acid metabolism activities, as well as the abundance of baca and sul1 resistance genes. These results expand our understanding of the interaction mechanism between APS and antibiotics in real aquatic environment.

Characterization of pyridine biodegradation by two Enterobacter sp. strains immobilized on Solidago canadensis L. stem derived biochar

In this study, two pyridine-degrading strains namely Enterobacter cloacae complex sp. BD17 and Enterobacter sp.BD19 were isolated from the aerobic tank of a pesticide wastewater treatment plant. The mixed bacteria H4 composed of BD17 and BD19 at a ratio of 1:1 was immobilized by Solidago canadensis L. stem biochar with a dosage of 2 g·L^-1. The highest pyridine removal rate of 91.70% was achieved by the immobilized H4 at an initial pyridine concentration of 200 mg·L^-1, pH of 7.0, temperature of 28 °C and salinity of 3.0% within 36 h. The main intermediates of pyridine degradation by BD17 were pyridine-2-carboxamide, 2-aminopropanediamide, and 2-aminoacetamide, while 2-picolinic acid, isopropyl acetate, isopropyl alcohol, and acetaldehyde were identified with BD19 by adopting GC-MS technique. Interestingly, there was a possibility of totally mineralization of pyridine and the corresponding degradation pathways of BD17 and BD19 were revealed for the first time.

How bioaugmentation with Comamonas testosteroni accelerates pyridine mono-oxygenation and mineralization

Pyridine is a common heterocycle found in industrial wastewaters. Its biodegradation begins with a mono-oxygenation reaction, and bioaugmentation with bacteria able to carry out this mono-oxygenation is one strategy to improve pyridine removal and mineralization. Although bioaugmentation has been used to enhance the biodegradation of recalcitrant organic compounds, the specific role played by the bioaugmented bacteria usually has not been addressed. We acclimated activated-sludge biomass for pyridine biodegradation and then isolated a strain -- Comamonas testosteroni -- based on its ability to biodegrade and grow on pyridine alone. Pyridine was removed faster by C. testosteroni, compared to pyridine-acclimated biomass, but pyridine mineralization was slower. Pyridine biodegradation and mineralization rates were accelerated when C. testosteroni was bioaugmented into the acclimated biomass, which increased the amount of C. testosteroni, but otherwise had minimal effects on the microbial community. The key role of C. testosteroni was to accelerate the first step of pyridine biodegradation, mono-oxygenation to 2-hydroxylpyridine (2HP), and the acclimated biomass was better able to complete downstream reactions leading to mineralization. Thus, bioaugmentation increased the rates of pyridine mono-oxygenation and subsequent mineralization through the synergistic roles of C. testosteroni and the main community in the acclimated biomass.

Pre-electrochemical treatment combined with fixed bed biofilm reactor for pyridine wastewater treatment: From performance to microbial community analysis

To overcome the high biotoxicity and poor biodegradability of pyridine and its derivatives, a pre-electrochemical treatment combined with fixed bed biofilm reactor (EC-FBBR) was designed for multi-component stream including pyridine (Pyr), 3-cyanopyridine (3-CNPyr), and 3-chloropyridine (3-ClPyr). The EC-FBBR system could simultaneously degrade these pollutants with a mineralization efficiency of 90%, especially for the persistent 3-ClPyr. Specifically, the EC could partially degrade all pollutants, and allow them to be completely destructed in FBBR. With EC off, Rhodococcus (35.5%) became the most abundant genus in biofilm, probably due to its high tolerance to 3-ClPyr. With EC on, 3-ClPyr was reduced to an acceptable level, thus Paracoccus (21.1%) outcompeted among interspecies competition with Rhodococcus and became the dominant genus. Paracoccus was considered to participate in the subsequent degradation for the residual 3-ClPyr, and led to the complete destruction for all pollutants. This study proposed promising combination for effective treatment of multi-component pyridine wastewater.