Abstract
Despite the adverse effects of emerging ZnO nanoparticles (nano-ZnO) on wastewater biological nitrogen removal (BNR) systems being widely documented, strategies for mitigating nanoparticle (NP) toxicity impacts on nitrogen removal have not been adequately addressed. Herein, N-acyl-homoserine lactone (AHL)-based quorum sensing (QS) was investigated for its effects against nano-ZnO toxicity to a model nitrifier, Nitrosomonas europaea. The results indicated that AHL-attenuated nano-ZnO toxicity, which was inversely correlated with the increasing dosage of AHL from 0.01 to 1 µM. At 0.01 µM, AHL notably enhanced the tolerance of N. europaea cells to nano-ZnO stress, and the inhibited cell proliferation, membrane integrity, ammonia oxidation rate, ammonia monooxygenase activity and amoA gene expression significantly increased by 18.2 ± 2.1, 2.4 ± 0.9, 58.7 ± 7.1, 32.3 ± 1.7, and 7.3 ± 5.9%, respectively, after 6 h of incubation. However, increasing the AHL dosage compromised the QS-mediated effects and even aggravated the NPs’ toxicity effects. Moreover, AHLs, at all tested concentrations, significantly increased superoxide dismutase activity, indicating the potential of QS regulations to enhance cellular anti-oxidative stress capacities when facing NP invasion. These results provide novel insights into the development of QS regulation strategies to reduce the impact of nanotoxicity on BNR systems.
Highlights
In recent decades, engineered nanomaterials have become an emerging class of materials [1].Diverse metallic nanoparticles (MNPs), displaying unique physical and chemical characteristics, have been broadly applied in commercial and industrial products, such as electronics, catalysts, pharmaceuticals, pigments, cosmetics, and textiles [2]
The objectives of this study were to exam the impacts of a typical exogenous quorum sensing (QS) signalling molecule, N-3-oxo-hexanoyl-homoserine lactone (3-oxo-C6 -HSL) addition on nano-ZnO toxicity to a model ammonia-oxidizing bacteria (AOB), Nitrosomonas europaea [25], which produces at least three types of acyl-homoserine lactone (AHL), including
AHLs at 0.1–0.5 μM only improved cell density and membrane integrity under nano-ZnO stress, while metabolic functions, including ammonia oxidation rate (AOR), ammonia monooxygenase (AMO) activity and amoA expression, were still inhibited or even deteriorated further (Figures 2 and 3). These results indicated that QS regulation for stress tolerance was dependent on the AHL dosing concentration
Summary
Diverse metallic nanoparticles (MNPs), displaying unique physical and chemical characteristics, have been broadly applied in commercial and industrial products, such as electronics, catalysts, pharmaceuticals, pigments, cosmetics, and textiles [2]. ZnO NPs (nano-ZnO), which have high water solubility, are among the most commonly used NPs, according to the Organization for Economic. Due to the unique optoelectronic and catalytic properties [4], ZnO and nano-ZnO have been widely applied in many products, including solar cells, electronic sensors, antibacterial agents, photocatalysts, sunscreen, batteries, and glass [5,6,7]. The increasing use of MNPs and their inevitable emissions into the environment [8] have caused an increase in research focus on their bio-safety and risks to ecosystems [5,9]. Public Health 2019, 16, 3003; doi:10.3390/ijerph16163003 www.mdpi.com/journal/ijerph
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