Enhanced enzyme activity through electron transfer between single-walled carbon nanotubes and horseradish peroxidase

Granular activated carbon and exogenous hydrogen enhanced anaerobic digestion of hypersaline phenolic wastewater via syntrophic acetate oxidation and hydrogenotrophic methanogenesis

High salinity in phenolic wastewater inhibited anaerobes' metabolic activity, thereby affecting the anaerobic biotransformation of phenol. In this study, granular activated carbon (GAC) coupled with exogenous hydrogen (H₂) was used to enhance the anaerobic digestion of phenol. The GAC/H₂ group's accumulative methane production, coenzyme F₄₂₀ concentration, and interspecies electron transfer system activity increased by 24 %, 53 %, and 16 %, respectively, compared with the control group. In the floc sludge of the GAC/H₂ group, the relative abundance of syntrophic acetate-oxidizing bacteria such as Syntrophus and Syntrophorhabdus were 18.7 % and 1.1 % at genus level, respectively, which were around 93.5 and 7.5 times of that of the controlgroup. Moreover, Acinetobacter (77.6 %), Methanobacterium (44.0 %), and Methanosarcina (34.2 %) were significantly enriched on the GAC surface in GAC/H₂ group. Therefore, the coupling of GAC and H₂ provided a novel attempt at anaerobic digestion of hypersaline phenolic wastewater via syntrophic acetate oxidation and hydrogenotrophic methanogenesis pathway.

Effects of cadmium sulfide nanoparticles on sulfate bioreduction and oxidative stress in Desulfovibrio desulfuricans

Sulfate-containing wastewater has a serious threat to the environment and human health. Microbial technology has great potential for the treatment of sulfate-containing wastewater. It was found that nano-photocatalysts could be used as extracellular electron donors to promote the growth and metabolic activity of non-photosynthetic microorganisms. However, nano-photocatalysts could also induce oxidative stress and damage cells. Therefore, the interaction mechanism between photosynthetic nanocatalysts and non-photosynthetic microorganisms is crucial to determine the regulatory strategies for microbial wastewater treatment technologies. In this paper, the mechanism and regulation strategy of cadmium sulfide nanoparticles (CdS NPs) on the growth of sulfate-reducing bacteria and the sulfate reduction process were investigated. The results showed that the sulfate reduction efficiency could be increased by 6.4% through CdS NPs under light conditions. However, the growth of Desulfovibrio desulfuricans C09 was seriously inhibited by 55% due to the oxidative stress induced by CdS NPs on cells. The biomass and sulfate reduction efficiency could be enhanced by 6.8% and 5.9%, respectively, through external addition of humic acid (HA). At the same time, the mechanism of the CdS NPs strengthening the sulfate reduction process by sulfate bacteria was also studied which can provide important theoretical guidance and technical support for the development of microbial technology combined with extracellular electron transfer (EET) for the treatment of sulfate-containing wastewater.

Coupling granular activated carbon and exogenous hydrogen to enhance anaerobic digestion of phenol via predominant syntrophic acetate oxidation and hydrogenotrophic methanogenesis pathway

Anaerobic digestion is a promising biological method for treating phenol-containing wastewater. However, the low methane yield of phenol due to the biological toxicity limits its potential application. This study presents a novel method to enhance the conversion rate of phenol to methane by coupling of granular activated carbon and exogenous hydrogen (GAC/H₂). The cumulative methane production in the GAC/H₂, H₂, GAC, and control groups were 408.2 ± 16.2, 336.5 ± 5.7, 287.2 ± 26. 2, and 258.1 ± 8.6 mL‬ CH₄/g COD, respectively. Compared with the control group, the hydrogenotrophic methanogenic activity and electron transfer activity of GAC/H₂ group were increased by 403.9 and 367.4%, respectively. The results of the 16SrRNA analysis indicated GAC enhanced the relative abundances of Syntrophus and Syntrophorhabdus, and hydrogen promoted the relative abundances of Cryptanaerobacter, Aminicenantes, and Methanobacterium. Therefore, the coupling of GAC and exogenous hydrogen promoted a dominate SAO-HM pathway to convert phenol to methane.

Effects of carbon nanotubes on biodegradation of pollutants: Positive or negative?

Recently, a large quantity of carbon nanotubes (CNTs) enters the environment due to the increasing production and applications. More and more researches are focused on the fate and possible ecological risks of CNTs. Some literatures summarized the effects of CNTs on the chemical behavior and fate of pollutants. However, little reviewed the effects of CNTs on the biodegradation of pollutants. In general, the effects of CNTs on the biodegradation of pollutants and the related mechanisms were summarized in this review. CNTs have positive or negative effects on the biodegradation of contaminants by affecting the functional microorganisms, enzymes and the bioavailability of pollutants. CNTs may affect the microbial growth, activity, biomass, community composition, diversity and the activity of enzymes. The decrease of the bioavailability of pollutants due to the sorption on CNTs also causes the reduction of the biodegradation of contaminants. In addition, the roles of CNTs are controlled by multiple mechanisms, which are divided into three aspects i.e., properties of CNTs, environment condition, and microorganisms themself. The better understanding of the fate of CNTs and their impacts on the biochemical process in the environment is conducive to determine the release of CNTs into the environment.

Multi-walled carbon nanotubes facilitated the removal of tetrabromobisphenol a mediated by horseradish peroxidase

In this study, we systematically investigated the effect of multiwall carbon nanotubes (MWCNTs) on the removal of tetrabromobisphenol A (TBBPA) mediated by horseradish peroxidase (HRP) at varying important conditions. The results suggested that the presence of MWCNTs significantly enhanced the removal of TBBPA mediated by HRP and the reaction rate constant was linear with the MWCNTs dosage. The enhancement of MWCNTs on the HRP-mediated reaction was attributed to two facts, one is that MWCNTs protected HRP from inactivation, the other is that the presence of MWCNTs made the homogeneous reaction of TBBPA be heterogeneous reaction by adsorbing TBBPA on its surface. Moreover, the influence of MWCNTs on TBBPA products distribution was further elucidated. We found that the species of reaction product had no difference between the HRP-mediated systems with and without the presence of MWCNTs. However, the presence of MWCNTs significantly decreased the yields of each product. These results give insight into the role of MWCNTs in HRP-mediated TBBPA reactions and provide theoretical foundation for potential development of novel enzymatic methods to control TBBPA contamination. MWCNTs enhanced the removal of TBBPA mediated by HRP/H₂O₂, because it protected HRP from inactivation and adsorbed TBBPA on its surface to form a heterogeneous reaction process.

Effects of carbon nanotubes on atrazine biodegradation by Arthrobacter sp

The environmental risks of engineered nanoparticles have attracted attention. However, little is known regarding the effects of carbon nanotubes (CNTs) on the biodegradation and persistence of organic contaminants in water. We investigated the impacts of pristine and oxidized multiwalled CNTs on the atrazine biodegradation rate and efficiency using Arthrobacter sp. At a concentration of 25mg/L, the CNTs enhanced the biodegradation rate by up to 20%; however, at a concentration of 100mg/L, the CNTs decreased the biodegradation rate by up to 50%. The stimulation effects resulted from enhanced bacterial growth and the overexpression of degradation genes. The inhibitory effects resulted from the toxicity of the CNTs at high concentrations. The differences between the two CNTs at tested concentrations were not significant. The biodegradation efficiency was not impacted by adsorption, and the pre-adsorbed atrazine on the CNTs was fully biodegraded when the CNT concentration was ≤25mg/L. This finding was consistent with the lack of observable desorption hysteresis for atrazine on the tested CNTs. Our results indicate that CNTs can enhance or inhibit biodegradation through a balance of two effects: the toxic effects on microbial activity and the effects of the changing bioavailability that result from adsorption and desorption.

pH-Switchable electroactive composite films of carboxylated multi-walled carbon nanotubes and Prussian blue

Here the combination of carboxylated multi-walled carbon nanotubes (CMWCNTs) and Prussian blue (PB) for fabricating pH-responsive electroactive composite thin films is reported.

Mechanistic Study on the Reduction of SWCNT-induced Cytotoxicity by Albumin Coating

Single walled carbon nanotubes (SWCNTs) are utilized in many areas, accompanied with the ever rising safety concerns. Coating the SWCNTs by serum albumin has shown promises in reduction of their cytotoxicity. The cause of toxicity reduction could be due to the blockage of cellular protein adsorption by bovine serum albumin (BSA). Here, our study explored the mechanism of toxicity reduction from the point of view of protein adsorption. Different loadings of BSA led to varied surface coverage of the SWCNTs, which was positively related to the level of cytotoxicity. In addition, the BSA-coated SWCNTs were tested for their surface morphology change, cellular uptake, and adsorption of cellular proteins. BSA could be competed off the SWCNT surface by the cytosol proteins, and thus a higher BSA loading was needed to provide better protection to the cells. Cellular uptake was also reduced with a higher BSA loading. Moreover, the BSA coating changed the surface property of SWCNTs, and as a consequence, altered the types of proteins adsorbed by the SWCNTs. Our results support that adsorption of BSA reduces cellular uptake of SWCNTs as well as adsorption of cellular proteins on SWCNTs, both contributing to the much lower cytotoxicity observed for the BSA-coated SWCNTs.

Degradation of phenolic compounds by laccase immobilized on carbon nanomaterials: diffusional limitation investigation

Carbon nanoparticles are promising candidates for enzyme immobilization. We investigated enzyme loading and laccase activity on various carbon nanoparticles, fullerene (C60), multi-walled carbon nanotubes (MWNTs), oxidized-MWNTs (O-MWNTs), and graphene oxide (GO). The loading capacity was highest for O-MWNTs and lowest for C60. The activity of laccase on various nanomatrices using 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTs) as a substrate decreased in the following order: GO>MWNTs>O-MWNTs>C60. We speculated that aggregation of the nanoparticles influenced enzyme loading and activity by reducing the available adsorption space and substrate accessibility. The nanoparticle-immobilized laccase was then used for removal of bisphenol and catechol substrates. Compared to free laccase, the immobilized enzymes had significantly reduced reaction rates. For example, the reaction rate of GO-laccase conjugated with bisphenol or catechol substrates was only 10.28% or 12.33%, respectively, of that of the free enzyme. Considering that there was no obvious structural change observed after enzyme immobilization, nanomatrix-induced diffusional limitation most likely caused the low reaction rates. These results demonstrate that the diffusional limitation induced by the aggregation of carbon nanoparticles cannot be ignored because it can lead to increased reaction times, low efficiency, and high economic costs. Furthermore, this problem is exacerbated when low concentrations of environmental contaminants are used.