A sensitive, wide-ranging comprehensive toxicity indicator based on microbial fuel cell

Effects of simulated microgravity on current generation of electrochemically active bacteria: Insights from case-control study using random positioning machine

Electrochemically active bacteria (EAB) exhibit promising prospects for space exploration and life support systems. However, the effects of the space environment on EAB are unclear. In this study, the effects of simulated microgravity on the current generation of mixed-culture EAB were illustrated, and the underlying mechanism was elucidated. The results demonstrated that the electrochemical activity of mixed-culture EAB was enhanced, which was mainly due to the enrichment of Geobacter and the increase in EAB biomass. Additionally, the genes and proteins of the biofilm changed obviously under simulated microgravity conditions, including: I) genes related to signal transfer, II) genes related to cell wall synthesis, and III) genes related to riboflavin synthesis. This study first revealed the enrichment in EAB abundance, the increase in EAB biomass, and the promotion of current generation under simulated microgravity.

Machine Learning in Bioelectrocatalysis

At present, the global energy crisis and environmental pollution coexist, and the demand for sustainable clean energy has been highly concerned. Bioelectrocatalysis that combines the benefits of biocatalysis and electrocatalysis produces high-value chemicals, clean biofuel, and biodegradable new materials. It has been applied in biosensors, biofuel cells, and bioelectrosynthesis. However, there are certain flaws in the application process of bioelectrocatalysis, such as low accuracy/efficiency, poor stability, and limited experimental conditions. These issues can possibly be solved using machine learning (ML) in recent reports although the combination of them is still not mature. To summarize the progress of ML in bioelectrocatalysis, this paper first introduces the modeling process of ML, then focuses on the reports of ML in bioelectrocatalysis, and ultimately makes a summary and outlook about current issues and future directions. It is believed that there is plenty of scope for this interdisciplinary research direction.

Biocathode prepared at low anodic potentials achieved a higher response for water biotoxicity monitoring after polarity reversal

Microbial electrochemical sensors equipped with biocathode sensing elements have attracted a growing interest, but their startup and recovery properties remain unclear. In this study, the approach of polarity reversal was applied for the biocathode sensing element fabrication and biosensor recovery. The stimulating/suppressing effect of formaldehyde was determined by the anode potential before polarity reversal as well as the increased trials of toxic exposure. Increasing anode potential from -0.3 V to +0.3 V before polarity reversal, the baseline electric signal was changed from -0.028 ± 0.001 mA to -0.005 ± 0.003 mA, while the maximum normalized electrical signal (NES) was increased from 1.1 ± 0.1 to 4.1 ± 1.9, and thus a general downtrend was observed for Response as a newly induced indicator. Polarity reversal failed to recover the electroactivity of these poisoned bioelectrodes. This study demonstrated that electrode potential was critical when using the approach of polarity reversal to construct the biocathode sensing element, and revealed an urgent need for strategies toward high recoverability of such biosensors.

Indicators of water biotoxicity obtained from turn-off microbial electrochemical sensors

The development of biosensors is critical to reducing potential risks associated with contamination accidents. However, the application of microbial electrochemical sensors for water biotoxicity monitoring is hampered by the lack of an indicator with high response magnitudes. In this study, microbial electrochemical sensors were fabricated with interdigitated electrode arrays (IDAs), and indicators from various electrochemical analyses were comprehensively investigated. Only the peak of cyclic voltammetry (CV) was highly linearly correlated with the commonly used current indicator during the enrichment of the electroactive biofilm. The resistance fitted from the electrochemical impedance spectroscopy (EIS) data provided a comparable and even higher inhibition ratio (IR) than the current during toxicity assessments. The differential pulse voltammetry (DPV) did not exhibit a higher sensitivity than the CV peak. However, no clear response was observed in the real-time impedance analysis for use in water biotoxicity monitoring. Most of the microbes were in the propidium iodide (PI)-permeable state after the toxicity assessments, although the current was fully recovered. This study demonstrates the potential to use EIS data as indicators of water biotoxicity using microbial electrochemical sensors.

Study on simplified strategies for procedure of rapid detection of water toxicity

In this work, a simplified procedure of detection of water toxicity based on Pt ultramicroelectrode (UME) and mixed microorganism cultured without sterilization was the first proposed. A stable Pt UME was successfully prepared with a special glass tube as insulation and support material, which was used as working electrode in the biosensor. The Pt UME exhibits the typical cyclic voltammogram (CV) of Pt UME with sigmoid shape and possesses good stability, enlarged current response and tunable dimension. In addition, it was an effective and simple method for toxicity biosensor using mixed microorganisms cultured in unsterilized lysogeny broth (LB) as the bioreceptor. K₃[Fe(CN)₆] was used as an electron mediator. Under the optimal conditions of 30 mM K₃[Fe(CN)₆], OD₆₀₀ = 1 cell concentration, and 50 mM phosphate-buffered solution (PBS), the half-maximal inhibitory concentration (IC₅₀) values measured for Cd²⁺, Cu²⁺ and Ni²⁺ were 3.99 mg/L, 1.16 mg/L and 2.37 mg/L, respectively. The results indicated that the biosensor with large diameter Pt UME and mixed microorganisms cultured in unsterilized LB realized rapid and simple detection of water toxicity.

Anode biofilm influence on the toxic response of microbial fuel cells under different operating conditions

The response of microorganisms in microbial fuel cells (MFCs) to toxic compounds under different operating conditions, such as flow rate and culture time, was investigated herein. While it has been reported that MFCs can detect some toxic substances, it is unclear if operating conditions affect MFCs toxicity response. In this study, the toxic response time of MFCs decreased when the flow rate increased from 0.5 mL/min to 2 mL/min and then increased with 5 mL/min. The inhibition rates at 0.5 mL/min, 2 mL/min, and 5 mL/min were 8.4% ± 1.6%, 45.1% ± 5.3%, and 4.9% ± 0.3%, respectively. With the increase of culture time from 7 days to 90 days, the toxic response time of MFCs gradually increased. The inhibition rates at culture times of 7 days, 45 days, and 90 days were 45.1% ± 5.3%, 32.6% ± 6.6%, and 23.2% ± 1.3%, respectively. Increasing the culture time will reduce the sensitivity of MFC. The results showed that MFCs can respond quickly at a flow rate of 2 mL/min after cultivation for 7 days. Under these conditions, the power density can reach 1137.0 ± 65.5 mW/m², the relative content of Geobacter sp. is 57%, and the ORP of the multilayers changed from -159.2 ± 1.6 mV to -269.9 ± 1.7 mV within 200 μm biofilm thickness. These findings show that increasing the flow rate and shortening the culture time are conducive for the toxicity response of MFCs, which will increase the sensitivity of MFCs in practical applications.

The evaluation of long term performance of microbial fuel cell based Pb toxicity shock sensor

Microbial fuel cell (MFC) sensor exhibits attractive prospects for online monitoring of water toxicity as an early warning device. However, the accumulation of dead cells in anode biofilm might decrease the sensing sensitivity of MFC during long term operation. In addition, with repeated exposure to toxins, the microbial community of anode biofilm would also adjust to build up higher endurance to environmental toxicity. In this study, the long term sensing sensitivity of MFC sensor and the microbial community changes were characterized with Pb²⁺ as the target toxin. The results show that newly formed biofilm with higher live/dead cell ratio exhibited higher sensitivity than mature biofilm. Modification of anodic biofilm via high current stimulation was applied to increase the ratio of live cells, which led to enhanced sensing sensitivity of MFC with mature anode biofilm. However, the enhancement was relatively limited for biofilm that was previously exposed to repeated Pb²⁺ shocks. Microbial community analysis revealed that the proportions of microbial species possessing higher environmental robustness, such as Hyphomicrobiaceae and Cloacibacillus, significantly increased in the anode biofilm after long term repeated Pb²⁺ shocks.

Micro-microbial electrochemical sensor equipped with combined bioanode and biocathode for water biotoxicity monitoring

The development of low-cost biosensors for water monitoring is expected to reduce potential risks from contamination accidents. This study reported a novel micro-microbial electrochemical sensor using combined bioanode and biocathode as the sensing element, characterized by a sequential flowing membrane-free channel and a bilateral passive oxygen supply. A decrease in the ratio of number of bioanode to biocathode resulted in a lower power generation, whereas, achieving a similar or even higher toxic response. The voltage was affected by both the flow rate and the acetate concentration. With the increased acetate concentration, a clear trade-off was observed between the electroactivity stimulation of bioanode vs. the electroactivity maintenance of biocathode. Biosensors made good response to the injection of formaldehyde (10 µL of 0.25%, and 100 µL of 0.025%) into the inlet. A high microbial diversity was observed. This work can lead to a revolutionizing way of water monitoring using self-powered micro-biosensors.

Effect of the tetracycline antibiotics on performance and microbial community of microbial fuel cell

The adverse effect of tetracycline antibiotics on microbial activity is one of the serious risks for the biologic wastewater treatment process. The microbial fuel cells (MFCs) are a promising technology for wastewater treatment and renewable power generation process. For this reason, the investigation of the inhibition effect of the tetracyclines on the MFCs is essential for reducing damage on the environment. This paper focused on the performance of MFCs under different antibiotic concentrations at the range of 0.25-50 mg/L. The power generation performance, microbial community and biofilm characteristics (morphology, resistance and viability) of MFCs were investigated in detail. The results indicated that the increase in the antibiotic concentration significantly affected the MFC performance and microbial community. A modified non-competitive inhibition model was used to predict the inhibition effect of tetracycline antibiotics on the MFCs.