Microbial electrode

The fouling and microbial contamination of the surface during operation are main problems in the long-term use of enzyme biosensors. Wang et al. [121] reported for the first time a screen-printed electrode modified with GOD/HRP that was stable up... 

A portable microbial sensing system [58] was developed for detecting the toxicity of pre-treated wastewater. The signal of the modified electrode containing a bacterial culture renewed every 9 h, within 8 min of contact with toxic solutions or samples, is roughly correlated with toxicity. 

Extensive review literature exists in the area of biological fuel cells. Notably, Palmore and Whitesides summarized biological fuel cell concepts and performance up to 1992." More recently, Katz and Willner discussed recent progress in novel electrode chemistries for both microbial and enzymatic fuel cells,and Heller reviewed advances in miniature cells.This article does not duplicate these valuable contributions. Instead, we focus on the strengths and weak-... 

Microbial biofuel cells were the earliest biofuel cell technology to be developed, as an alternative to conventional fuel cell technology. The concept and performance of several microbial biofuel cells have been summarized in recent review chapters." The most fuel-efficient way of utilizing complex fuels, such as carbohydrates, is by using microbial biofuel cells where the oxidation process involves a cascade of enzyme-catalyzed reactions. The two classical methods of operating the microbial fuel cells are (1) utilization of the electroactive metabolite produced by the fermentation of the fuel substrate " and (2) use of redox mediators to shuttle electrons from the metabolic pathway of the microorganism to the electrodes. ... 

Aucoteam GmbH, Berlin, Germany BODyPoint BOD Microbial electrode Waste water... 

Central Kagaku Corp., Tokyo, Japan BOD-2000 BOD Microbial electrode Sewage and waste water... 

Kelma, Niel, Belgium RODTOX Short time BOD, toxicity Microbial reactor + Oj electrode Municipal and industrial waste water... 

Microbial sensors offer a number of assets, namely (a) they are less sensitive to inhibition by solutes and more tolerant to suboptimal pH and temperature values than are enzyme electrodes b) they have longer lifetimes than enzymes and (c) they are less expensive than enzyme electrodes as they require no active enzyme to be isolated. On the other hand, they lag behind enzyme electrodes in a few other respects thus, (a) some have longer response times than their enzyme counterparts b) baseline restoration after measurement typically takes longer and (c) cells contain many enzymes and due care must be exercised to ensure adequate selectivity e.g. by optimizing the storage conditions or using specific enzyme reactions) —some mutant microorganisms lack certain enzymes. 

A novel bioassay for nystatin based on the use of a microbial sensor was recently reported. Nystatin is believed to bind to the steron present in the membranes of sensitive cells, leading to the formation of pores. The subsequent death of the microorganism is preceded by leakage of cellular materials. Microbial death can be detected by means of an oxygen electrode. 

Table 10. Microbial sensors for the detection of aromatic pollutants using oxygen electrodes... 

Karube I, Matsimaga T, Mitsuda S, Suzuki S (1977) Microbial electrode BOD sensor. Biotechn Bioeng 19 1535-1547... 

Figure 1. Schematic diagram of the microbial electrode sensor for glucose.

The sensitivity of the microbial sensor was almost the same as that of common enzyme electrodes. Furthermore, the microbial sensor was more stable than enzyme electrodes when they were applied to determine glucose in molasses. 

Alcohol Sensor. On-line measurements of ethyl alcohol concentration in culture broth are required in fermentation industries. A microbial electrode consisting of immobilized yeasts or bacteria, a gas permeable Teflon membrane, and an oxygen electrode was prepared for the determination of methyl and ethyl alcohols(7). 

A microbial sensor consisting of immobilized methyl alcohol-utilizing bacteria (AJ 3993), a gas permeable membrane, and an oxygen electrode was applied to the determination of methyl alcohol. A linear relaionship was also observed between the current decrease and the concentration of methyl alcohol. Therefore, the sensor can be also applied to the determination of methyl alcohol. 

Cephalosporin is determined from the proton concentration generated in a medium by using immobilized bacteria. A microbial sensor composed of a bacteria-collagen membrane reactor and a combined glass electrode was applied to the determination of cephalosporins in fermentation media. The system used for continuous determination... 

Therefore, ammonia is determined by a microbial sensor using immobilized nitrifying bacteria and an oxygen electrode(12-14)(Figure 6). 

The sensitivity of the microbial sensor was almost at the same level as that of a ammonia electrode. The sensor did not respond to volatile compounds such as acetic acid, ethyl alcohol and amines... 

Therefore, NO2 generated in the buffer (pH 2.0) can be determined by the microbial sensor using immobilized Nitrobacter sp. and an oxygen electrode(20,21). The scheme of the microbial sensor system is illustrated in Figure 9. 

Figure 9. Schematic diagram of the nitrite sensor system. l.Air(28(Mj/ min) 2. Pump 3. Buffer (pH 2.0) 4. Sample solution> 5- Peristaltic pump 6. Pump 7. Valve 8. Incubator (30 C) 9. Microbial electrode 10. Waste 11. Amplifier 12. Recorder 13. Electrolyte (30% sodium hydroxide) 14. Teflon membrane 15. Buffer (pH 2.0) containing HCh gas 16. Immobilized whole cells 17. Gas permeable membrane ...

The microbial sensor system is shown in Figure 10. The electrode system consisted of two microbial electrodes the electrode of B. subtilis Rec" (Rec- electrode) and the electrode of B subtilis Rec -(Recf electrode). Each electrode was composed of immobilized bacteria and an oxygen electrode. 

This microbial sensor system is based on the inhibitory action of the mutagens on the respiration of B subtilis Rec . B subtilis M45 (Rec") is genetically deficient in the DNA recombination enzyme system, whereas B subtilis H17 (Rec+) is a wild strain which has the ability to repair damaged DNA. The subsequent death of Rec bacteria is preceded by the decrease of respiration. As a result, the number of Rec cells on the surface of the oxygen electrode decreased and the current of the Rec electrode increased. On the other hand, the damaged DNA of Rec+ bacteria is repaired with the recombination system. Therefore, the number of Rec+ cells did not change and the current of the Rec electrode did not increase. 

When typhimurium was incubated with chemical mutagens such as N-methyl-N -nitro-N-nitrosoguanidine, nitrofurazone, methyl me-thanesulfonate, and ethyl methanesulfonate, for 10 h the current decrease of the electrode was measured. The response of the electrode increased with increasing concentration of chemical mutagens. Therefore, the mutagenicity of chemicals can be estimated with the microbial electrode. 

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