Growth curves of <i>E</i>. <i>coli</i> in different concentrations of MH (A) and LB broth media (B).

<p>Growth curves of <i>E</i>. <i>coli</i> in different concentrations of MH (A) and LB broth media (B).</p

Dose-response curves of SAs, Ery and their mixtures in 0.4-fold diluted MH broth at 24 h.

<p>Dose-response curves of SAs, Ery and their mixtures in 0.4-fold diluted MH broth at 24 h.</p

An analogous wood barrel theory to explain the occurrence of hormesis: A case study of sulfonamides and erythromycin on <i>Escherichia coli</i> growth

<div><p>Hormesis has aroused much attention during the past two decades and may have great implications on many fields, including toxicology and risk assessment. However, the observation of hormesis remains challenged under laboratory conditions. To determine favorable conditions under which to observe hormesis, we investigated the hormetic responses of <i>Escherichia</i> <i>coli</i> (<i>E</i>. <i>coli</i>) upon exposure of different concentrations of sulfonamides and erythromycin at different time points and in different culture media: Luria-Bertani (LB) broth and Mueller Hinton (MH) broth. Our results reveal that the antibiotics, both individually and combined, produce hormetic effects on <i>E</i>. <i>coli</i> growth in MH broth at the stationary phase, with the maximum stimulatory response increasing with time. However, in LB broth, the hormetic response was not observed, which can be explained by an analogous “wood barrel theory”. Our study suggests that the culture medium and time should be taken into consideration in hormetic studies, and compound mixtures should also receive more attention for their potential to induce hormesis.</p></div

Graphic illustration of the analogous “wood barrel theory”.

<p>(A) The culture medium is compared to a wood barrel with irregular lengths, among which the utilizable carbon source is the shortest one. (B) The growth of <i>E</i>. <i>coli</i> in LB broth was limited by the utilizable carbon source, for which hormesis in LB broth did not show up. (C) <i>E</i>. <i>coli</i> upon exposure to antibiotics in MH broth was stimulated to make full use of the utilizable carbon source, which leads to a length increase of the shortest board for MH broth, and thus showed a hormetic response.</p

Dose-response curves of (A) SMZ and (B) Ery in 0.4-fold diluted MH broth at different time points.

<p>Dose-response curves of (A) SMZ and (B) Ery in 0.4-fold diluted MH broth at different time points.</p

Dose-response curves of antibiotics towards <i>E</i>. <i>coli</i> in different broth media.

<p>(A) SMZ in MH broth; (B) Ery in MH broth; (C) SMZ in LB broth and (D) Ery in LB broth.</p

Concentration-response curves for mixtures of SMZ (A), SD (B) and SM (C) with Ery in 0.4-fold diluted MH broth at different time points.

<p>Concentration-response curves for mixtures of SMZ (A), SD (B) and SM (C) with Ery in 0.4-fold diluted MH broth at different time points.</p

Model of Hormesis and Its Toxicity Mechanism Based on Quorum Sensing: A Case Study on the Toxicity of Sulfonamides to <i>Photobacterium phosphoreum</i>

During the past two decades, the phenomenon of hormesis has gained increasing recognition in environmental and toxicological communities. However, the mechanistic understanding of hormesis, to date, is extremely limited. Herein is proposed a novel parametric model with a mechanistic basis and two model-based parameters for hormesis that was successfully applied to the hormetic dose–response observed in the chronic toxicity of sulfonamides on <i>Photobacterium phosphoreum</i>. On the basis of the methods of molecular docking and quantitative structure–activity relationships (QSARs), we proposed a mechanistic hypothesis for hormesis that introduces for the first time the concept of quorum sensing in toxicological studies and explains the mechanism at the level of the receptors. The mechanistic hypothesis stated that (1) specific target binding like interaction with LuxR may contribute to transcriptional activation leading to enhanced luciferase activity at low dose exposure of sulfonamides, and (2) as the dose of sulfonamides increases, more sulfonamides competitively bind to dihydropteroate synthase, which inhibit the biosynthesis of folic acid and thus provoke toxicity. This mechanistic hypothesis, which explains both the dose-dependent and time-dependent features of hormesis, could give new insight into the mechanistic study of hormesis

Efficient Oxidative Debromination of Decabromodiphenyl Ether by TiO₂‑Mediated Photocatalysis in Aqueous Environment

Direct evidence was first demonstrated for the oxidative degradation of decabromodiphenyl ether (BDE209) in aqueous TiO₂ dispersions under UV irradiation (λ > 340 nm). BDE209 was hardly debrominated over TiO₂ in UV-irradiated acetonitrile dispersions, but the addition of water into the dispersions greatly enhanced its photocatalytic oxidative debromination. The debromination efficiency of BDE209 as high as 95.6% was achieved in aqueous TiO₂ dispersions after 12 h of UV irradiation. The photocatalytic oxidation of BDE209 resulted in generation of aromatic ring-opening intermediates such as brominated dienoic acids, which were further degraded by prolonging UV irradiation time. The photocatalytic oxidative debromination of BDE209 was further confirmed by the observation that the BDE209 degradation in water–acetonitrile mixtures with different water contents was positively correlated with the formation of •OH radicals, but not photogenerated electrons. The use of water not only avoided the scavenging of reactive radicals by organic solvent but also enhanced the adsorption of BDE209 on the surface of TiO₂, both of which favor the contact of BDE209 with photogenerated holes and •OH species. The confirmation of efficient oxidative degradation and debromination of BDE209 is very important for finding new ways to remove polybrominated diphenyl ethers from the environment