Towards the development of a new generation of whole-cell bioreporters to sense iron bioavailability in oceanic systems-learning from the case of Synechococcus sp. PCC7002 iron bioreporter

Use of whole-cell bioreporters to assess bioavailability of contaminants in aquatic systems

Water contamination has become increasingly a critical global environmental issue that threatens human and ecosystems’ health. Monitoring and risk assessment of toxic pollutants in water bodies is essential to identifying water pollution treatment needs. Compared with the traditional monitoring approaches, environmental biosensing via whole-cell bioreporters (WCBs) has exhibited excellent capabilities for detecting bioavailability of multiple pollutants by providing a fast, simple, versatile and economical way for environmental risk assessment. The performance of WCBs is determined by its elements of construction, such as host strain, regulatory and reporter genes, as well as experimental conditions. Previously, numerous studies have focused on the design and construction of WCB rather than improving the detection process and commercialization of this technology. For investigators working in the environmental field, WCB can be used to detect pollutants is more important than how they are constructed. This work provides a review of the development of WCBs and a brief introduction to genetic construction strategies and aims to summarize key studies on the application of WCB technology in detection of water contaminants, including organic pollutants and heavy metals. In addition, the current status of commercialization of WCBs is highlighted.

Comparative Analysis of Cell Metabolic Activity Sensing by Escherichia coli rrnB P1-lux and Cd Responsive-Lux Biosensors: Time-Resolved Experiments and Mechanistic Modelling

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) time-resolved measurements of bioluminescence produced by constitutive rrnB P1-luxCDABE Escherichia coli 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 PzntA-luxCDABE E. coli 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 theoretical interpretation for the time-dependent response of biosensors to unravel metabolic and physicochemical contributions to the bioluminescence signal.

Exploiting Catabolite Repression and Stringent Response to Control Delay and Multimodality of Bioluminescence Signal by Metal Whole-Cell Biosensors: Interplay between Metal Bioavailability and Nutritional Medium Conditions

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-luxCDABE Escherichia coli 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.

Demarcating antioxidant response against aluminum induced oxidative stress in Westiellopsis prolifica Janet 1941

Aluminum metal pollution is considered as a primary limiting factor that reduced crop yield in South Asian subtropical country like India. In national context, Odisha contributes around more than 40% of total ore availability. Moreover, industrial mining and smelting aid are major concern for aluminum metal toxicity in territorial vicinity affecting the soil fertility, ecosystem and human health through food chain. The aluminum metal accumulation limits the soil fertility by antagonistic regulation of photosynthetic and nitrogen fixing microbiota. The increasing concern regarding aluminum pollution enterprise critical investigations for their bioremediation in contamination sites. In this notion, the current study was hypothesized to decrypt the rate limiting factors, their explicit mode of action and intracellular detoxification in a cyanobacterium, i.e., Westiellopsis prolifica isolated from ash pond of NALCO (National Aluminum Company Limited), Angul, Odisha. In the experimental setup, treatment with different concentrations of AlCl₃ (0-0.1 mM) was marked a decline in the growth of the strain due to the adverse regulation of photosynthetic pigments. However, the enforcement of catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), guaiacol peroxidase (GPX) and glutathione reductase (GR) was critical for sustaining strain viability under oxidative imbalance. The observation of an increase in the antioxidant enzyme and MDA content was evident to sustain strain viability under such oxidative imbalance. The outcome of the anticipated study was apparent to demonstrate a colossal interlink between Al mediated induction of oxidative stress and their cellular detoxification via intracellular antioxidant enzymes and removal of H₂O₂ accumulation in cyanobacterium, W. prolifica. Statement of novelty Aluminum metal toxicity renders growth of Westiellopsis prolifica via affecting photosynthesis associated pigments. Westiellopsis prolifica deploys antioxidant defense enzymes to combat against aluminum mediated oxidative upset. Intracellular antioxidant enzymes provoke cellular survival of Westiellopsis prolifica under excessive uptake of aluminum in contaminated habitats.