Abstract
Toxicity mechanisms of metal oxide nanoparticles towards bacteria and underlying roles of membrane composition are still debated. Herein, the response of lipopolysaccharide-truncated
...Escherichia coli
K12 mutants to TiO
2
nanoparticles (TiO
2
NPs, exposure in dark) is addressed at the molecular, single cell, and population levels by transcriptomics, fluorescence assays, cell nanomechanics and electrohydrodynamics. We show that outer core-free lipopolysaccharides featuring intact inner core increase cell sensitivity to TiO
2
NPs. TiO
2
NPs operate as membrane strippers, which induce osmotic stress, inactivate cell osmoregulation and initiate lipid peroxidation, which ultimately leads to genesis of membrane vesicles. In itself, truncation of lipopolysaccharide inner core triggers membrane permeabilization/depolarization, lipid peroxidation and hypervesiculation. In turn, it favors the regulation of TiO
2
NP-mediated changes in cell Turgor stress and leads to efficient vesicle-facilitated release of damaged membrane components. Remarkably, vesicles further act as electrostatic baits for TiO
2
NPs, thereby mitigating TiO
2
NPs toxicity. Altogether, we highlight antagonistic lipopolysaccharide-dependent bacterial responses to nanoparticles and we show that the destabilized membrane can generate unexpected resistance phenotype.
Whole-cell bacterial sensors are used in medical/environmental applications to detect chemicals, and to assess medium toxicity or stress. Non-specific constitutive biosensors generally serve the ...latter purpose, whereas chemical detection is performed with biosensors involving a specific chemical-inducible promoter. Herein, we show that functioning principles of specific and non-specific whole-cell biosensors are not exclusive as both can probe modulations of cell metabolic activity under stressing conditions. The demonstration is based on (i)
measurements of bioluminescence produced by constitutive
P1-
biosensor in media differing with respect to carbon source, (ii) theoretical reconstruction of the measured signals using a here-reported theory for bioluminescence generated by constitutive cells, (iii) comparison between time-dependent cell photoactivity (reflecting metabolic activity) retrieved by theory with that we reported recently for cadmium-inducible P
-
in media of similar compositions. Whereas signals of constitutive and non-constitutive biosensors differ in terms of shape, amplitude and peak number depending on nutritional medium conditions, analysis highlights the features shared by their respective cell photoactivity patterns mediated by the interplay between stringent response and catabolite repressions. The work advocates for the benefits of a
to unravel metabolic and physicochemical contributions to the bioluminescence signal.
The time-dependent response of metal-detecting whole-cell luminescent bacterial sensors is impacted by metal speciation/bioavailability in solution. The comprehensive understanding of such ...connections requires the consideration of the bacterial energy metabolism at stake and the effects of supplied food on cells' capability to convert bioaccumulated metals into light. Accordingly, we investigated the time response (48 h assay) of PzntA-
Cd biosensors in media differing with respect to sources of amino acids (tryptone or Lysogeny Broth) and carbon (glucose, xylose and mixtures thereof). We show that the resulting coupling between the stringent cell response and glucose/xylose-mediated catabolite repressions lead to well-defined multimodalities and shapes of the bioluminescence signal over time. Based on a recent theory for the time-response of metal-sensing luminescent bacteria, successful theoretical reconstructions of the bioluminescence signals are reported under all Cd concentrations (0-20 nM) and nutritive conditions examined. This analysis leads to the evaluation of time-dependent cell photoactivity and qualitative information on metal speciation/bioavailability in solution. Biosensor performance and the position, shape, number, and magnitude of detected peaks are discussed in relation to the metabolic pathways operative during the successive light emission modes identified here over time. Altogether, the results clarify the contributions of metal/nutrient bio-availabilities and food quality to cell response typology.
Arsenic-resistant prokaryote diversity is far from being exhaustively explored. In this study, the arsenic-adapted prokaryotic community present in a moderately arsenic-contaminated site near ...Sainte-Marie-aux-Mines (France) was characterized, using metaproteomic and 16S rRNA-encoding gene amplification. High prokaryotic diversity was observed, with a majority of Proteobacteria, Acidobacteria and Bacteroidetes, and a large archaeal community comprising Euryarchaeaota and Thaumarchaeota. Metaproteomic analysis revealed that Proteobacteria, Planctomycetes and Cyanobacteria are among the active bacteria in this ecosystem. Taken together, these results highlight the unsuspected high diversity of the arsenic-adapted prokaryotic community, with some phyla never having been described in highly arsenic-exposed sites.
Large‐scale production and incorporation of titanium dioxide nanoparticles (NP‐TiO2) in consumer products leads to their potential release into the environment and raises the question of their ...toxicity. The bactericidal mechanism of NP‐TiO2 under UV light is known to involve oxidative stress due to the generation of reactive oxygen species. In the dark, several studies revealed that NP‐TiO2 can exert toxicological effects. However, the mode of action of these nanoparticles is still controversial. In the present study, we used a combination of fluorescent probes to show that NP‐TiO2 causes Escherichia coli membrane depolarization and loss of integrity, leading to higher cell permeability. Using both transcriptomic and proteomic global approaches we showed that this phenomenon translates into a cellular response to osmotic stress, metabolism of cell envelope components and uptake/metabolism of endogenous and exogenous compounds. This primary mechanism of bacterial NP‐TiO2 toxicity is supported by the observed massive cell leakage of K+/Mg2+ concomitant with the entrance of extracellular Na+, and by the depletion of intracellular ATP level.
In the present study, we conducted a 2 week microcosm experiment with a natural freshwater bacterial community to assess the effects of titanium dioxide nanoparticles (TiO2-NPs) at various ...concentrations (0, 1, 10 and 100 mg/L) on planktonic and sessile bacteria under dark conditions. Results showed an increase of planktonic bacterial abundance at the highest TiO2-NP concentration, concomitant with a decrease from that of sessile bacteria. Bacterial assemblages were most affected by the 100 mg/L TiO2-NP exposure and overall diversity was found to be lower for planktonic bacteria and higher for sessile bacteria at this concentration. In both compartments, a 100 mg/L TiO2-NPs exposure induced a decrease in the ratio between the Betaproteobacteria and Bacteroidetes. For planktonic communities, a decrease of Comamonadaceae was observed concomitant with an increase of Oxalobacteraceae and Cytophagaceae (especially Emticicia). For sessile communities, results showed a strong decrease of Betaproteobacteria and particularly of Comamonadaceae.
•Microcosm experiments with natural water exposed to TiO2-NPs.•Toxicity of TiO2-NPs assessed on both planktonic and sessile bacteria.•Effects on bacterial community structure and diversity.•Shift occurs in the Betaproteobacteria/Bacteroidetes repartition in communities.
TiO2-NPs increase abundance of planktonic bacteria, decrease that of sessile bacteria, and affect diversity and structure of communities in both cases.
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•Response of bioluminescent metal whole-cell biosensors is measured under nutritional stress conditions.•Lack of amino acid leads to stringence-mediated mono- to bi-modal ...bioluminescence signal transition.•Response dependence on medium nutritional quality is rationalized by theory.•Photoactivity of biosensors varies non-linearly with bioluminescence.•Derived cells photoactivity remarkably agrees with data on rrnB P1-luxCDABE bioreporters.
Whole cell luminescent bacterial sensors are used to monitor the bioavailability and toxicity of metals in aquatic media. Any rationale of the time response of such metal-detecting biosensors necessarily asks for the so-far missing measurement and modeling of the impacts of medium nutritional quality on lux-reporter expression and bioluminescence production. In this work, improvement of nutritional conditions in bioluminescence assays by increasing amino acid concentration is shown to generate a transition from metal concentration-dependent monomodal to bimodal bell-shaped signal. The long-term component of the latter features a stringence-mediated adaptation of the cells to deficiency in nutrients supply from the medium. The demonstration is based on the analysis of the ∼17 h response of bioluminescent Escherichia coli engineered with luxCDABE reporter genes placed under the transcriptional control of a cadmium (0−22 nM bulk solution concentration) inductible-PzntA promoter or of the ribosomal RNA rrnB P1 promoter repressed by (p)ppGpp alarmones synthesized by cells in nutritional stress. The time-dependence of normalized PzntA-luxCDABE biosensor signal is successfully reproduced by our recent theory elaborated for the kinetics of bioluminescence emission by metal-responsive biosensors. The formalism allows assessment of luciferase half-life and of the time variations of cells photoactivity with medium composition. The theoretically-determined long-term kinetics of cell photoactivation is remarkably supported by independent measurements on the rrnB P1-luxCDABE bioreporter. Results clarify the origin of the mismatch between maxima in photoactive biomass and in bioluminescence over time, and they offer practical options for addressing contaminant toxicity via cell photoactivity derived from deconvolution of normalized biosensor response.
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► NP-TiO2 may affect the viability of Escherichia coli in the absence of light. ► Interfacial electrostatic interactions play a paramount role in the toxicity. ► Physico-chemical ...parameters are fundamental in controlling the interactions. ► This study provides knowledge essential to a better assessment of NP toxicity.
The increasing production and use of titanium dioxide nanoparticles (NP-TiO2) has led to concerns about their possible impact on the environment. Bacteria play crucial roles in ecosystem processes and may be subject to the toxicity of these nanoparticles. In this study, we showed that at low ionic strength, the cell viability of Escherichia coli was more severely affected at pH 5.5 than at pH 7.0 and pH 9.5. At pH 5.5, nanoparticles (positively charged) strongly interacted with the bacterial cells (negatively charged) and accumulated on their surfaces. This phenomenon was observed in a much lower degree at pH 7.0 (NP-TiO2 neutrally charged and cells negatively charged) and pH 9.5 (both NP-TiO2 and cells negatively charged). It was also shown that the addition of electrolytes (NaCl, CaCl2, Na2SO4) resulted in a gradual reduction of the NP-TiO2 toxicity at pH 5.5 and an increase in this toxicity at pH 9.5, which was closely related to the reduction of the NP-TiO2 and bacterial cell electrostatic charges.
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