Microplate freeze-dried cyanobacterial bioassay for fresh-waters environmental monitoring

A novel simultaneous short-course nitrification, denitrification and fermentation process: bio-enhanced phenol degradation and denitrification in a single reactor

The feasibility of a simultaneous nitrification, denitrification and fermentation process (SNDF) under electric stirrer agitation conditions was verified in a single reactor. Enhanced activated sludge for phenol degradation and denitrification in pharmaceutical phenol-containing wastewater under low dissolved oxygen conditions, additional inoculation with Comamonas sp. BGH and optimisation of co-metabolites were investigated. At a hydraulic residence time (HRT) of 28 h, 15 mg/L of substrate as strain BGH co-metabolised substrate degraded 650 ± 50 mg/L phenol almost completely and was accompanied by an incremental increase in the quantity of strain BGH. Strain BGH showed enhanced phenol degradation. Under trisodium citrate co-metabolism, strain BGH combined with activated sludge treated phenol wastewater and degraded NO2--N from 50 ± 5 to 0 mg/L in only 7 h. The removal efficiency of this group for phenol, chemical oxygen demand (COD) and TN was 99.67%, 90.25% and 98.71%, respectively, at an HRT of 32 h. The bioaugmentation effect not only promotes the degradation of pollutants, but also increases the abundance of dominant bacteria in activated sludge. Illumina MiSeq sequencing research showed that strain BGH promoted the growth of dominant genera (Acidaminobacter, Raineyella, Pseudarcobacter) and increased their relative abundance in the activated sludge system. These genera are resistant to toxicity and organic matter degradation. This paper provides some reference for the activated sludge to degrade high phenol pharmaceutical wastewater under the action of biological enhancement.

Engineered live bacteria as disease detection and diagnosis tools

Sensitive and minimally invasive medical diagnostics are essential to the early detection of diseases, monitoring their progression and response to treatment. Engineered bacteria as live sensors are being developed as a new class of biosensors for sensitive, robust, noninvasive, and in situ detection of disease onset at low cost. Akin to microrobotic systems, a combination of simple genetic rules, basic logic gates, and complex synthetic bioengineering principles are used to program bacterial vectors as living machines for detecting biomarkers of diseases, some of which cannot be detected with other sensing technologies. Bacterial whole-cell biosensors (BWCBs) can have wide-ranging functions from detection only, to detection and recording, to closed-loop detection-regulated treatment. In this review article, we first summarize the unique benefits of bacteria as living sensors. We then describe the different bacteria-based diagnosis approaches and provide examples of diagnosing various diseases and disorders. We also discuss the use of bacteria as imaging vectors for disease detection and image-guided surgery. We conclude by highlighting current challenges and opportunities for further exploration toward clinical translation of these bacteria-based systems.

On-site determination of water toxicity based on freeze-dried electrochemically active bacteria

Our previous studies have reported water toxicity determination with a fresh electrochemically active bacteria (EAB) suspension as the sensing element, which exhibits high sensitivity and has great prospects in providing early warning about water pollution. However, because the preparation of fresh EAB suspensions is time-consuming, these studies are not suitable for the on-site determination of water toxicity. To solve this problem, this study investigated the rapid preparation of an EAB suspension by the rehydration of freeze-dried EABs and established a novel method for the on-site determination of water toxicity based on the freeze-dried EAB model strain Shewanella oneidensis MR-1. The results demonstrate that the optimal cryoprotectant for S. oneidensis MR-1 freeze drying is 7.5 % (w/v) skimmed milk powder. Compared with fresh S. oneidensis MR-1, freeze-dried S. oneidensis MR-1 exhibits similar extracellular electron transfer (EET) performance (74.7 % ± 0.3 %) and slightly lower sensitivity for water toxicity determination (65.8 % ± 2.2 %) with the optimal cryoprotectant. On-site determination of water toxicity was realized by using freeze-dried S. oneidensis MR-1, and the detection limits of five common toxic pollutants (Cd²⁺, Pb²⁺, Cu²⁺, phenol and dichlorophenol) reached 0.5 mg/L. Water toxicity determination is capable of resisting common interferences, e.g., glucose, lactate, nitrate and nitrite, and shows high accuracy in practical applications.

Biological and technical challenges for implementation of yeast-based biosensors

Biosensors are low-cost and low-maintenance alternatives to conventional analytical techniques for biomedical, industrial and environmental applications. Biosensors based on whole microorganisms can be genetically engineered to attain high sensitivity and specificity for the detection of selected analytes. While bacteria-based biosensors have been extensively reported, there is a recent interest in yeast-based biosensors, combining the microbial with the eukaryotic advantages, including possession of specific receptors, stability and high robustness. Here, we describe recently reported yeast-based biosensors highlighting their biological and technical features together with their status of development, that is, laboratory or prototype. Notably, most yeast-based biosensors are still in the early developmental stage, with only a few prototypes tested for real applications. Open challenges, including systematic use of advanced molecular and biotechnological tools, bioprospecting, and implementation of yeast-based biosensors in electrochemical setup, are discussed to find possible solutions for overcoming bottlenecks and promote real-world application of yeast-based biosensors.

Development of portable whole-cell biosensing platform with lyophilized bacteria and its application for rapid on-site detection of heavy metal toxicity without pre-resuscitation

The high toxicity of heavy metals necessitates monitoring technology that allows rapid adaptation and deployment. Microbial whole-cell biosensors have become a priority because of their excellent performance. However, traditional methods have several limitations, including long assay time, poor portability, and the lack of ready-to-use on-site devices. In this study, a novel portable whole-cell biosensing platform was developed by integrating a simple handheld fiber-optic dissolve oxygen sensor and bacterial culture or lyophilized bacteria. Based on the oxygen consumption inhibition mechanism, this platform achieved rapid acute toxicity measurement of heavy metal ions through inhibit Escherichia coli (E.coli) respiration. Under the optimal conditions, the limit of detection and IC50 of Hg²⁺ using E. coli culture were 5.62 μM and 11.64 μM, respectively. Interestingly, the lyophilized E. coli could be directly applied for Hg²⁺ toxicity detection without pre-resuscitation, where an IC50 of 31.28 μM was obtained, and the whole detection process was only 18 min. The lyophilized E. coli could be stored long-term at -80 °C without significant loss of activity and detection performance. The portable whole-cell biosensing platform demonstrated a high potential for rapid on-demand toxicity detection in real water samples. The developed strategy is not only fast, portable, and easily storable, but also highly suited for on-site ready-to-use, and high-frequency toxicity detection of heavy metal ions in the field.

Microbial whole-cell biosensors: Current applications, challenges, and future perspectives

Microbial Whole-Cell Biosensors (MWCBs) have seen rapid development with the arrival of 21st century biological and technological capabilities. They consist of microbial species which produce, or limit the production of, a reporter protein in the presence of a target analyte. The quantifiable signal from the reporter protein can be used to determine the bioavailable levels of the target analyte in a variety of sample types at a significantly lower cost than most widely used and well-established analytical instrumentation. Furthermore, the versatile and robust nature of MWCBs shows great potential for their use in otherwise unavailable settings and environments. While MWCBs have been developed for use in biomedical, environmental, and agricultural monitoring, they still face various challenges before they can transition from the laboratory into industrialized settings like their enzyme-based counterparts. In this comprehensive and critical review, we describe the underlying working principles of MWCBs, highlight developments for their use in a variety of fields, detail challenges and current efforts to address them, and discuss exciting implementations of MWCBs helping redefine what is thought to be possible with this expeditiously evolving technology.

Portable, Disposable, Paper-Based Microbial Fuel Cell Sensor Utilizing Freeze-Dried Bacteria for In Situ Water Quality Monitoring

Water quality monitoring is becoming an essential part of our lives as increasing human activities continue to spill unknown and unexpected contaminants into our water systems. To ensure the provision of safe and clean water to the public and the ecosystem, the development of rapid and sensitive in situ early warning systems for water toxicity monitoring is crucial. In this work, an entirely paper-based microbial fuel cell sensor utilizing freeze-dried bacteria is demonstrated as a portable and disposable water toxicity sensor. The bacterial cells were preinoculated on the anode reservoir of the device, and they were freeze-dried, making their on-site and on-demand applications possible. Upon rehydration of the bacteria with the water samples, current readings were obtained, and inhibition ratios (IRs) were calculated for different concentrations of formaldehyde as a model toxin. For 0.001, 0.01, and 0.02% of formaldehyde, IRs of 7.88, 16.08, and 23.14% were obtained, respectively. These IRs showed a very good linearity with the formaldehyde concentrations at R ² = 0.995. Additionally, the shelf life of the freeze-dried microbial fuel cell sensor was investigated. Even after 14 days of storage in the desiccator, at 4, and at -20 °C, the performance outputs compared to the new device were all at 96%.

Artificial inorganic biohybrids: The functional combination of microorganisms and cells with inorganic materials

Biohybrids can be defined as the functional combination of proteins, viable cells or microorganisms with non-biological materials. This article reviews recent findings on the encapsulation of microorganisms and eukaryotic cells in inorganic matrices such as silica gels or cements. The entrapment of biological entities into a support material is of great benefit for processing since the encapsulation matrix protects sensitive cells from shear forces, unfavourable pH changes, or cytotoxic solvents, avoids culture-washout, and simplifies the separation of formed products. After reflecting general aspects of such an immobilization as well as the chemistry of the inorganic matrices, we focused on manufacturing aspects and the application of such biohybrids in biotechnology, medicine as well as in environmental science and for civil engineering purpose.

STATEMENT OF SIGNIFICANCE

The encapsulation of living cells and microorganisms became an intensively studied and rapidly expanding research field with manifold applications in medicine, bio- and environmental technology, or civil engineering. Here, the use of silica or cements as encapsulation matrices have the advantage of a higher chemical and mechanical resistance towards harsh environmental conditions during processing compared to their polymeric counterparts. In this perspective, the article gives an overview about the inorganic material systems used for cell encapsulation, followed by reviewing the most important applications. The future may lay in a combination of the currently achieved biohybrid systems with additive manufacturing techniques. In a longer perspective, this would enable the direct printing of cell loaded bioreactor components.