Carbon nanotubes mitigate copper-oxide nanoparticles-induced inhibition to acidogenic metabolism of Propionibacterium acidipropionici by regulating carbon source utilization

Elucidation of the stress mechanisms on activated sludge stability induced by yttrium oxide nanoparticles with cytotoxicity: Performance deterioration, biointerface variation and microbial response

As technoscience advances, widespread use of nanoparticles (NPs) has resulted in environmental risks. This study focuses on the potential stress of 0-200 mg/L yttrium oxide (Y2O3) NPs on the activated sludge stability. Y2O3 NPs progressively suppressed nitrification, caused significant NO2- accumulation (200 mg/L) and diminished activities of key functional enzymes. Deteriorated flocculation corroborates the Y2O3 NPs' destruction. Extracellular polymeric substances were lessened, yet amplified microbial metabolites prove the microbial counteraction coping with Y2O3 NPs' cytotoxicity. Plausible blockage of different protein channels contributed to the wane in biological nitrogen-removal capacity. Plus, 50 mg/L Y2O3 NPs stimulated the β-glucan production. When exceeding 100 mg/L, plentiful Y2O3 NPs aggregate on sludge-surface, which inhibits nutrients transfer and metabolism. Furthermore, ammonia-oxidizing bacteria shifted from Nitrosomonas to Nitrosospira with Y2O3 NPs increase. Reduction in Nitrospira, Saccharimonada-genera, and Microlunatus further corroborates the impairment of pollutants removal. PICRUSt2 prediction demonstrates Y2O3 NPs impedes nitrogen and glycolytic metabolic pathway.

Overlooked roles of improved substrates functions in remodeling microbial community and driving metabolic traits during sludge fermentation triggered by surfactants and antibiotics co-existence

Sludge anaerobic fermentation is a pivotal route to transit wastewater treatment plants towards energy-neutral and resource recovery-oriented plants, while the overall efficiency is commonly restrained by co-exist contaminants. This study unveiled the cooperative effect of sulfadiazine (SDZ) and linear alkylbenzene sulfonates (LAS) in driving volatile fatty acids (VFAs) biosynthesis during waste activated sludge (WAS) anaerobic fermentation. The VFAs remarkably elevated to 1189 mg COD/L in LAS/SDZ, which was approximately 1.3-3.2 folds of SDZ and LAS. SDZ and LAS synergistically disintegrated extracellular polymeric substances to provide fermentation substrates. These changes altered microbial population and enhanced microbial networks interconnection. Moreover, the proteins released from WAS might facilitate electron transfer among microorganisms. The functional anaerobic species, including hydrolytic-acidogenic bacteria (e.g., Veillonellaceae and Lactobacillus) and electroactive bacteria (e.g., Parabacteroides and Fonticella), were enriched. Also, the metabolic traits responsible for transmembrane transport, intracellular metabolism, VFAs biosynthesis and electron transfer-related process were strengthened with the upregulation of functional genes. Further analysis revealed that the functional anaerobic species activated quorum sensing and two-component systems to counteract unfavorable LAS/SDZ stress and maintain high metabolic activities. This work elucidated the overlooked roles of substrates in modulating anaerobic consortia and metabolic traits in sludge fermentation systems with mixed pollutants stressing.

Metagenomics insight into bioaugmentation mechanism of Propionibacterium acidipropionici during anaerobic acidification of kitchen waste

In the present study, a biochemical strategy for improving propionic acid production from kitchen waste acidification by bioaugmentation with Propionibacterium acidipropionici (P. acidipropionici) was investigated. When the inoculum of P. acidipropionici was 30% (w/w) of the seeding sludge, the propionic acid production increased by 79.57%. Further, bioaugmentation improved the relative abundance of Firmicute and Actinobacteria. The results of metagenomic analysis further reveal that the ATP-binding cassette (ABC) transporters and all related pathways of Propanoate metabolism (ko00640) were enriched when P. acidipropionici was added. For Propanoate metabolism, most functional genes involved in the conversion from Glycolysis / Gluconeogenesis (ko00010) to Propanoyl-CoA and conversion from Propanoyl-CoA to propionic acid were enhanced after bioaugmentation with P. acidipropionici, thereby promoting propionic acid production. As such, bioaugmentation with P. acidipropionici was effective in the anaerobic acidification of kitchen waste for propionic acid production.

Enhancement of hexavalent chromium reduction by Shewanella oneidensis MR-1 in presence of copper nanoparticles via stimulating bacterial extracellular electron transfer and environmental adaptability

The bioreduction of hexavalent chromium (Cr(VI)) depends highly on bacterial activity, while the release of copper nanoparticles (Cu NPs) poses threats to microorganisms in the environment. This work demonstrated that Cr(VI) reduction efficiency of Shewanella oneidensis MR-1 was remarkably enhanced by 83.7% under 20 mg/L Cu NPs exposure. Cu NPs improved the electron migration capacity of Shewanella oneidensis MR-1 by enhancing bioelectrochemical performance and flavin mononucleotide secretion. Moreover, key genes related to extracellular electron transfer pathways, including direct electron transfer through outer-membrane proteins, flavin-mediated electron transfer, and conductive flagella, were generally upregulated under Cu NPs exposure. In addition, environmental adaptability of Shewanella oneidensis MR-1 was enhanced under Cu NPs exposure by improving environmental information processing and energy and reducing power production, promoting Cr(VI) reduction by Shewanella oneidensis MR-1. This work indicated that Cu NPs could enhance Cr(VI) reduction by Shewanella oneidensis MR-1 through regulating extracellular electron transfer and environmental adaptability.

Transcriptomic response of Pseudomonas nicosulfuronedens LAM1902 to the sulfonylurea herbicide nicosulfuron

The overuse of the herbicide nicosulfuron has become a global environmental concern. As a potential bioremediation technology, the microbial degradation of nicosulfuron shows much promise; however, the mechanism by which microorganisms respond to nicosulfuron exposure requires further study. An isolated soil-borne bacteria Pseudomonas nicosulfuronedens LAM1902 displaying nicosulfuron, chlorimuron-ethyl, and cinosulfuron degradabilities in the presence of glucose, was used to determine the transcriptional responses to nicosulfuron exposure. RNA-Seq results indicated that 1102 differentially expressed genes (DEGs) were up-regulated and 702 down-regulated under nicosulfuron stress. DEGs were significantly enriched in “ABC transporters”, “sulfur metabolism”, and “ribosome” pathways (p ≤ 0.05). Several pathways (glycolysis and pentose phosphate pathways, a two-component regulation system, as well as in bacterial chemotaxis metabolisms) were affected by nicosulfuron exposure. Surprisingly, nicosulfuron exposure showed positive effects on the production of oxalic acid that is synthesized by genes encoding glycolate oxidase through the glyoxylate cycle pathway. The results suggest that P. nicosulfuronedens LAM1902 adopt acid metabolites production strategies in response to nicosulfuron, with concomitant nicosulfuron degradation. Data indicates that glucose metabolism is required during the degradation and adaptation of strain LAM1902 to nicosulfuron stress. The present studies provide a glimpse at the molecular response of microorganisms to sulfonylurea pesticide toxicity and a potential framework for future mechanistic studies.

Long-term effects of copper nanoparticles on volatile fatty acids production from sludge fermentation: Roles of copper species and bacterial community structure

The long-term effects of copper nanoparticles (Cu NPs) on volatile fatty acids (VFAs) production during the waste activated sludge (WAS) fermentation, and the underlying mechanisms regarding copper species distribution and bacterial community evolution were explored. The yield of VFAs in the control was 1086 mg COD/L, whereas those were inhibited by 11.1%, 56.0% and 83.1%, with 25, 50, and 100 mg/g-TSS Cu NPs, respectively. Further investigation indicated that Cu NPs severely affected hydrolysis and acidification of WAS in a dose-dependent manner, while had little impact on solubilization. Besides, Cu NPs enriched the acid-consuming anaerobe while reducing the acid-forming bacteria. The metabolic pathways, microbial function, and enzymatic activities involved were inhibited at all tested dosages. Moreover, soluble and acid-extractable fractions dominated the copper speciation, which were also the main factors inhibiting the VFA production. This study provides a new perspective to interpret the long-term impacts of Cu NPs on WAS fermentation.

The combined toxicity and mechanism of multi-walled carbon nanotubes and nano copper oxide toward freshwater algae: Tetradesmus obliquus

Nanoparticles (NPs) are widely used for their special physical properties and released into the natural environment. When two types of NPs exist in the same environment, the presence of one type of NP may affect the properties of the other type of NP. This study investigated the toxic effects of multi-walled carbon nanotubes (MWCNTs) and copper oxide nanoparticles (CuO NPs) on Tetradesmus obliquus. Both NPs had toxic effects on algae, and the toxic effects of MWCNTs were significantly stronger than CuO NPs which the 96-hr median effective concentration to algae were 33.8 and 169.2 mg/L, respectively. Oxidative stress and cell membrane damage were the main reasons for the toxicity of NPs to algae, and they were concentration-dependent, and the existence of CuO NPs in some groups reduced cell membrane damage caused by MWCNTs which may because that CuO NPs formed heteroaggregation with MWCNTs, reducing the contact of nanoparticles with cell membranes, then reducing physical damage. Scanning electron microscopy (SEM) and transmission electron microscope (TEM) results indicated cell damage, the heteroaggregation of MWCNTs-CuO NPs and obvious nanoparticles internalization. In some groups, the presence of CuO NPs significantly reduced reactive oxygen species (ROS) level induced by MWCNTs. However, for the highest concentration group, the ROS level was much higher than that of the two NPs alone treatment groups, which might be related to the high concentration of MWCNTs promoting the internalization of CuO NPs. MWCNTs and CuO NPs affected and interacted with each other, causing more complex toxic effects on aquatic organisms.

Anaerobic bacterial responses to carbonaceous materials and implications for contaminant transformation: Cellular, metabolic, and community level findings

Carbonaceous materials (CM) enhance the abundance and activity of bacteria capable of persistent organic (micro)pollutant (POP) degradation. This review synthesizes anaerobic bacterial responses to minimally modified CM in non-fuel cell bioremediation applications at three stages: attachment, metabolism, and biofilm genetic composition. Established relationships between biological behavior and CM surface properties are identified, but temporal relationships are not well understood, making it difficult to connect substratum properties and "pioneer" bacteria with mature microorganism-CM systems. Stark differences in laboratory methodology at each temporal stage results in observational, but not causative, linkages as system complexity increases. This review is the first to critically examine relationships between material and cellular properties with respect to time. The work highlights critical knowledge gaps that must be addressed to accurately predict microorganism-CM behavior and to tailor CM properties for optimized microbial activity, critical frontiers in establishing this approach as an effective bioremediation strategy.

Anaerobic digestion beyond biogas

Anaerobic digestion (AD) is a matured technology for waste (water) remediation/stabilization and bioenergy generation in the form of biogas. AD technology has several inherent benefits ranging from generating renewable energy, remediating waste (water), and reducing greenhouse gas emission to improving health/hygiene and the overall socio-economic status of rural communities in developing nations. In recent years, there has been a paradigm shift in applications of AD technology beyond biogas. This special issue (SI) entitled, "Anaerobic Digestion Beyond Biogas (ADBB-2021)," was conceptualized to incorporate some of the recent advances in AD in which the emphasis is beyond biogas, such as anaerobic biorefinery, chain elongation, treatment of micropollutants, toxicity and system stability, digestate as biofertilizer, bio-electrochemical systems, innovative bioreactors, carbon sequestration, biogas upgrading, microbiomes, waste (water) remediation, residues/waste pre-treatment, promoter addition, and modeling, process control, and automation, among others. This VSI: ADBB-2021 contains 53 manuscripts (14 critical reviews and 39 research). The key findings of each manuscript are briefly summarized here, which can serve as a valuable resource for AD researchers to learn of major advances in AD technology and identify future research directions.

Joint effects of carbon nanotubes and copper oxide nanoparticles on fermentation metabolism towards Saccharofermentans acetigenes: Enhancing environmental adaptability and transcriptional expression

In this study, the joint effects of widely used copper oxide nanoparticles (CuO NPs) and multi-walled carbon nanotubes (MWCNTs) on the fermentation metabolism of a model acetogenic bacterium Saccharofermentans acetigenes were investigated and the underlying mechanisms were further explored. The presence of sole CuO NPs or MWCNTs severely inhibited the acetate generation, while their co-existences did not further decrease the acetate yield as expected. Further analysis indicated the joint effects facilitated the enhancement of bacterial stimulus response to the environment and interspecies communication, which improved adaptive capacity to the adverse environment involved in nanomaterials. Meanwhile, the co-existence reduced inhibitory effects of sole nanomaterial on the gene expressions and catalytic activities of key enzymes involved in glycolysis and pyruvate metabolism. Therefore, the joint effects could enhance environmental adaptation of S. acetigenes and transcriptional expressions of key enzymes for acetic acid production-related processes, alleviating the inhibition of CuO NPs to acetate production.