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Stable isotope labeling is a standard technique for tracing material transfer in molecular, ecological and biogeochemical studies. The main assumption in this approach is that the enrichment with a heavy isotope has no effect on the organism metabolism and growth, which is not consistent with current theoretical and empirical knowledge on kinetic isotope effects. Here, we demonstrate profound changes in growth dynamics of the green alga Raphidocelis subcapitata grown in 15N-enriched media. With increasing 15N concentration (0.37 to 50 at%), the lag phase increased, whereas maximal growth rate and total yield decreased; moreover, there was a negative relationship between the growth and the lag phase across the treatments. The latter suggests that a trade-off between growth rate and the ability to adapt to the high 15N environment may exist. Remarkably, the lag-phase response at 3.5 at% 15N was the shortest and deviated from the overall trend, thus providing partial support to the recently proposed Isotopic Resonance hypothesis, which predicts that certain isotopic composition is particularly favorable for living organisms. These findings confirm the occurrence of KIE in isotopically enriched algae and underline the importance of considering these effects when using stable isotope labeling in field and experimental studies.

Chemical synthesis of the conducting polymer polypyrrole induced by [Fe(CN) 6 ] 3− is reported. Reaction kinetics were characterized spectrophotometrically. Reaction rate was evaluated at several different pH levels in the presence of [Fe(CN) 6 ] 3− and [Fe(CN) 6 ] 4− ions. The formation of polypyrrole at aerobic and anaerobic conditions was evaluated. We report that at anaerobic conditions [Fe(CN) 6 ] 4− cannot initiate oxidative polymerization, while its oxidized form [Fe(CN) 6 ] 3− successfully initiates and maintains the pyrrole polymerization reaction. The formation of polypyrrole was also observed in the solution containing a pyrrole monomer, [Fe(CN) 6 ] 4− and dissolved oxygen due to re-oxidation (redox cycling) of [Fe(CN) 6 ] 4− into [Fe(CN) 6 ] 3− by dissolved oxygen. Experiments to determine the polymerization reaction rate were performed and showed the highest rate in the presence of 0.5 mM of [Fe(CN) 6 ] 3− at pH 9.0, while the polymerization reaction performed at pH 7.0 was determined as the slowest. This investigation opens new horizons for the application of [Fe(CN) 6 ] 4− /[Fe(CN) 6 ] 3− -based redox cycling reactions in the synthesis of the conducting polymer polypyrrole and potentially in the formation of other conducting polymers which can be formed by oxidative polymerization.

This review focuses on the overview of microbial amperometric biosensors and microbial biofuel cells (MFC) and shows how very similar principles are applied for the design of both types of these bioelectronics-based devices. Most microorganism-based amperometric biosensors show poor specificity, but this drawback can be exploited in the design of microbial biofuel cells because this enables them to consume wider range of chemical fuels. The efficiency of the charge transfer is among the most challenging and critical issues during the development of any kind of biofuel cell. In most cases, particular redox mediators and nanomaterials are applied for the facilitation of charge transfer from applied biomaterials towards biofuel cell electrodes. Some improvements in charge transfer efficiency can be achieved by the application of conducting polymers (CPs), which can be used for the immobilization of enzymes and in some particular cases even for the facilitation of charge transfer. In this review, charge transfer pathways and mechanisms, which are suitable for the design of biosensors and in biofuel cells, are discussed. Modification methods of the cell-wall/membrane by conducting polymers in order to enhance charge transfer efficiency of microorganisms, which can be potentially applied in the design of microbial biofuel cells, are outlined. The biocompatibility-related aspects of conducting polymers with microorganisms are summarized.

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Currently, Ag/AgCl-based reference electrodes are used in most electrochemical biosensors and other bioelectrochemical devices. However, standard reference electrodes are rather large and do not always fit within electrochemical cells designed for the determination of analytes in low-volume aliquots. Therefore, various designs and improvements in reference electrodes are critical for the future development of electrochemical biosensors and other bioelectrochemical devices. In this study, we explain a procedure to apply common laboratory polyacrylamide hydrogel in a semipermeable junction membrane between the Ag/AgCl reference electrode and the electrochemical cell. During this research, we have created disposable, easily scalable, and reproducible membranes suitable for the design of reference electrodes. Thus, we came up with castable semipermeable membranes for reference electrodes. Performed experiments highlighted the most suitable gel formation conditions to achieve optimal porosity. Here, Cl− ion diffusion through the designed polymeric junctions was evaluated. The designed reference electrode was also tested in a three-electrode flow system. The results show that home-built electrodes can compete with commercial products due to low reference electrode potential deviation (~3 mV), long shelf-life (up to six months), good stability, low cost, and disposability. The results show a high response rate, which makes in-house formed polyacrylamide gel junctions good membrane alternatives in the design of reference electrodes, especially for these applications where high-intensity dyes or toxic compounds are used and therefore disposable electrodes are required.

Due to global energy crisis the research for green renewable energy has skyrocketed in a past few years. Yeast based microbial fuel cell (MFC) is one of the many MFC...