Optimization of preservation conditions of As (III) bioreporter bacteria

Variability in Maize Seed Bacterization and Survival Correlating with Root Colonization by Pseudomonas Isolates with Plant-Probiotic Traits

Seed treatment with plant growth-promoting bacteria represents the primary strategy to incorporate them into agricultural ecosystems, particularly for crops under extensive management, such as maize. In this study, we evaluated the seed bacterization levels, root colonization patterns, and root competitiveness of a collection of autochthonous Pseudomonas isolates that have demonstrated several plant-probiotic abilities in vitro. Our findings indicate that the seed bacterization level, both with and without the addition of various protectants, is specific to each Pseudomonas strain, including their response to seed pre-hydration. Bacterization kinetics revealed that while certain isolates persisted on seed surfaces for up to 4 days post-inoculation (dpi), others experienced a rapid decline in viability after 1 or 2 dpi. The observed differences in seed bacterization levels were consistent with the root colonization densities observed through confocal microscopy analysis, and with root competitiveness quantified via selective plate counts. Notably, isolates P. protegens RBAN4 and P. chlororaphis subsp. aurantiaca SMMP3 demonstrated effective competition with the natural microflora for colonizing the maize rhizosphere and both promoted shoot and root biomass production in maize assessed at the V3 grown stage. Conversely, P. donghuensis SVBP6 was detected at very low levels in the maize rhizosphere, but still exhibited a positive effect on plant parameters, suggesting a growth-stimulatory effect during the early stages of plant development. In conclusion, there is a considerable strain-specific variability in the maize seed bacterization and survival capacities of Pseudomonas isolates with plant-probiotic traits, with a correlation in their root competitiveness under natural conditions. This variability must be understood to optimize their adoption as inputs for the agricultural system. Our experimental approach emphasizes the critical importance of tailoring seed bacterization treatments for each inoculant candidate, including the selection and incorporation of protective substances. It should not be assumed that all bacterial cells exhibit a similar performance.

Immobilization of fluorescent bacterial bioreporter for arsenic detection

Whole-cell bacterial biosensors hold great promise as a practical complementary approach for in-field detection of arsenic. Although there are various bacterial bioreporter systems for arsenic detection, fewer studies reported the immobilization of arsenic bioreporters. This study aimed at determining immobilization of specific bacterial bioreporter in agar and alginate biopolymers to measure level of arsenite and/or arsenate. To achieve sensitive detection, immobilization parameters of polymer concentration and cell density were evaluated. Moreover, by changing the culture medium, immobilized bioreporter cells in minimal medium can detect arsenite while they can detect both arsenite and arsenate in phosphate-limited minimal medium. When optimal parameters were applied, agar and alginate immobilized bioreporter systems can detect arsenite and arsenate concentrations of 10 μg/l and 200 μg/l within 5 h and 2 h, respectively. The results showed that the immobilized bacterial bioreporter systems are able to determine the concentrations of the two abundant species of arsenic; arsenite and arsenate, as opposed to other studies which reported only arsenite detection. This is the first study describe agar hydrogel and alginate bead immobilization of fluorescent arsenic bacterial bioreporter that can detect both arsenite and arsenate at the safe drinking water limit. Thus, this study will enable further steps to be taken towards developing sensitive and selective portable devices to assess environmental arsenic contamination and prevent acute arsenic toxicity.

A low cost color-based bacterial biosensor for measuring arsenic in groundwater

Using arsenic (As) contaminated groundwater for drinking or irrigation has caused major health problems for humans around the world, raising a need to monitor As level efficiently and economically. This study developed a color-based bacterial biosensor which is easy-to-use and inexpensive for measuring As and could be complementary to current As detecting techniques. The arsR-lacZ recombinant gene cassette in nonpathogenic strain Escherichia coli DH5α was used in the color-based biosensor which could be observed by eyes or measured by spectrometer. The developed bacterial biosensor demonstrates a quantitative range from 10 to 500μgL(-1) of As in 3-h reaction time. Furthermore, the biosensor was able to successfully detect and estimate As concentration in groundwater sample by measuring optical density at 595nm (OD595). Among different storage methods used in this study, biosensor in liquid at 4°C showed the longest shelf life about 9d, and liquid storage at RT and cell pellet could also be stored for about 3-5d. In conclusion, this study showed that the As biosensor with reliable color signal and economical preservation methods is useful for rapid screening of As pollutant, providing the potential for large scale screening and better management strategies for environmental quality control.

Recent Advances in Genetic Technique of Microbial Report Cells and Their Applications in Cell Arrays

Microbial cell arrays have attracted consistent attention for their ability to provide unique global data on target analytes at low cost, their capacity for readily detectable and robust cell growth in diverse environments, their high degree of convenience, and their capacity for multiplexing via incorporation of molecularly tailored reporter cells. To highlight recent progress in the field of microbial cell arrays, this review discusses research on genetic engineering of reporter cells, technologies for patterning live cells on solid surfaces, cellular immobilization in different polymers, and studies on their application in environmental monitoring, disease diagnostics, and other related fields. On the basis of these results, we discuss current challenges and future prospects for novel microbial cell arrays, which show promise for use as potent tools for unraveling complex biological processes.

Preservation of H₂ production activity in nanoporous latex coatings of Rhodopseudomonas palustris CGA009 during dry storage at ambient temperatures

To assess the applicability of latex cell coatings as an ‘off-the-shelf’ biocatalyst, the effect of osmoprotectants, temperature, humidity and O₂ on preservation of H₂ production in Rhodopseudomonas palustris coatings was evaluated. Immediately following latex coating coalescence (24 h) and for up to 2 weeks of dry storage, rehydrated coatings containing different osmoprotectants displayed similar rates of H₂ production. Beyond 2 weeks of storage, sorbitol-treated coatings lost all H₂ production activity, whereas considerable H₂ production was still detected in sucrose- and trehalose-stabilized coatings. The relative humidity level at which the coatings were stored had a significant impact on the recovery and subsequent rates of H₂ production. After 4 weeks storage under air at 60% humidity, coatings produced only trace amounts of H₂ (0–0.1% headspace accumulation), whereas those stored at < 5% humidity retained 27–53% of their H₂ production activity after 8 weeks of storage. When stored in argon at < 5% humidity and room temperature, R. palustris coatings retained full H₂ production activity for 3 months, implicating oxidative damage as a key factor limiting coating storage. Overall, the results demonstrate that biocatalytic latex coatings are an attractive cell immobilization platform for preservation of bioactivity in the dry state.

A multi-channel bioluminescent bacterial biosensor for the on-line detection of metals and toxicity. Part II: technical development and proof of concept of the biosensor

This research study deals with the on-line detection of heavy metals and toxicity within the context of environmental pollution monitoring. It describes the construction and the proof of concept of a multi-channel bioluminescent bacterial biosensor in immobilized phase: Lumisens3. This new versatile device, designed for the non-stop analysis of water pollution, enables the insertion of any bioluminescent strains (inducible or constitutive), immobilized in a multi-well removable card. The technical design of Lumisens3 has benefited from both a classical and a robust approach and includes four main parts: (1) a dedicated removable card contains 64 wells, 3 mm in depth, arranged in eight grooves within which bacteria are immobilized, (2) this card is incubated on a Pelletier block with a CCD cooled camera on top for bioluminescence monitoring, (3) a fluidic network feeds the card with the sample to be analyzed and finally (4) a dedicated computer interface, BIOLUX 1.0, controls all the elements of the biosensor, allowing it to operate autonomously. The proof of concept of this biosensor was performed using a set of four bioluminescent bacteria (Escherichia coli DH1 pBzntlux, pBarslux, pBcoplux, and E. coli XL1 pBfiluxCDABE) in the online detection of CdCl(2) 0.5 μM and As(2)O(3) 5 μM from an influent. When considering metals individually, the "fingerprints" from the biosensor were as expected. However, when metals were mixed together, cross reaction and synergistic effects were detected. This biosensor allowed us to demonstrate the simultaneous on-line cross detection of one or several heavy metals as well as the measurement of the overall toxicity of the sample.

Bioluminescence of Pseudomonas fluorescens HK44 in the course of encapsulation into silica gel. Effect of methanol

The bioluminescence (BLM) and colony-forming units (CFU) of Pseudomonas fluorescens HK44 were monitored during encapsulation into pre-polymerized Si(OMe)₄. The non-induced BLM of free cells was increased in the presence of 0.5-2.5 % MeOH. After mixing silica sol with the cell suspension, both BLM and CFU dropped to 1-3 and 8-18 %, respectively; both remained lowered as long as the silica biofilm contained residual MeOH. The kinetics of MeOH being released from silica biofilms (a thickness of 2-6 mm) were first-order. The decrease of bacterial activity due to encapsulation was proportional to the biofilm thickness. MeOH evolving during encapsulation is probably the principal stress factor but not the only one.

Whole-cell biochips for bio-sensing: integration of live cells and inanimate surfaces

Recent advances in the convergence of the biological, chemical, physical, and engineering sciences have opened new avenues of research into the interfacing of diverse biological moieties with inanimate platforms. A main aspect of this field, the integration of live cells with micro-machined platforms for high throughput and bio-sensing applications, is the subject of the present review. These unique hybrid systems are configured in a manner that ensures positioning of the cells in designated patterns, and enables cellular viability maintenance, and monitoring of cellular functionality. Here we review both animate and inanimate surface properties and how they affect cellular attachment, describe relevant modifications of both types of surfaces, list technologies for platform engineering and for cell deposition in the desired configurations, and discuss the influence of various deposition and immobilization methods on the viability and performance of the immobilized cells.

Development of bacteria-based bioassays for arsenic detection in natural waters

Arsenic contamination of natural waters is a worldwide concern, as the drinking water supplies for large populations can have high concentrations of arsenic. Traditional techniques to detect arsenic in natural water samples can be costly and time-consuming; therefore, robust and inexpensive methods to detect arsenic in water are highly desirable. Additionally, methods for detecting arsenic in the field have been greatly sought after. This article focuses on the use of bacteria-based assays as an emerging method that is both robust and inexpensive for the detection of arsenic in groundwater both in the field and in the laboratory. The arsenic detection elements in bacteria-based bioassays are biosensor-reporter strains; genetically modified strains of, e.g., Escherichia coli, Bacillus subtilis, Staphylococcus aureus, and Rhodopseudomonas palustris. In response to the presence of arsenic, such bacteria produce a reporter protein, the amount or activity of which is measured in the bioassay. Some of these bacterial biosensor-reporters have been successfully utilized for comparative in-field analyses through the use of simple solution-based assays, but future methods may concentrate on miniaturization using fiberoptics or microfluidics platforms. Additionally, there are other potential emerging bioassays for the detection of arsenic in natural waters including nematodes and clams.