Complete Genome Sequence of Pseudomonas Stutzeri S116 Provides Insights into the Mechanism of Microbial Fuel Cells

To identify suitable biocatalysts applied in microbial fuel cells (MFCs), Pseudomonas stutzeri S116 isolated from marine sludge was investigated, which possessed excellcent bioelectricity generation ability (BGA). Herein, P. stutzeri as a bioanode and biocathode achieved maximum output voltage (254.2 mV and 226.0 mV), and power density of (765 mW/m2 and 656.6 mW/m2). Complete genome sequencing of P. stutzeri was performed to reveal its potential microbial functions. The results exhibited that the strain was the ecologically dominant Pseudomonas, and its primary annotations were associated with energy production and conversion (6.84%), amino acid transport and metabolism (6.82%) and inorganic ion transport and metabolism (6.77%). The thirty-six genes involved in oxidative phosphorylation indicate that strain possesses an integrated electron transport chain. Moreover, many genes encoding redox mediators (mainly riboflavin and phenazine) were detected in the databases. Simultaneously, thiosulfate oxidization and dissimilatory nitrate reduction were annotated in the sulfur metabolism and nitrogen metabolism pathway. Gene function and cyclic voltammetry (CV) analysis indicated BGA of P. stutzeri probably was attributed to its cytochrome c and redox mediators, which enhance extracellular electron transfer (EET) rate.

Modelling Miniature Microbial Fuel Cells with Three-dimensional Anodes

Microbial fuel cells (MFCs) exploit the metabolic activity of electroactive microorganisms for oxidation of organic compounds and extracellular electron transfer to an external electrode. the technology is associate with very slowreaction rates, resulting in low current densities. Anodes with high specific surface should be used to increase the overall electricity generation. Carbon-based 3D materials, with high surface per unit of volume, are largely used anode materials in MFCs, although may show significant lack in efficiency due to mass transfer limitations, concentration gradients, velocity distribution and resistivity of the material. Consequently, the concomitant effect of several parameters should be assessed and quantified to design highly performing MFCs implementing 3D anode materials. In this work, miniature MFCs with 3D anodes are mathematically modelled to quantify the effect of operative parameters on performance. The model combines equations of charge conservation, mass transport phenomena, hydrodynamics, and kinetics of the involved processes under transient conditions, and provides 3D profiles with time of velocity, biofilm thickness, substrate concentration, current density and potential. The solution predicts a laminar flow, as it was expected with the low flow rates used. The concentration profiles show the consumption of substrate in the anode, with low values of local concentrations depending on organic load in the feed stream. The model also provides a versatile tool to optimise the operative conditions of the system, managing the flow arrangements to maximise either substrate removal or electricity generation.

Effects of CdS NPs on Sulfate Bioreduction and Oxidative Stress to Desulfovibrio Desulfuricans

Sulfate-containing wastewater has a serious threat to the environment and human health. Microbial technology has great potential for the treatment of sulfate-containing wastewater. It was found that nano-photocatalysts could be used as extracellular electron donors to promote the growth and metabolic activity of non-photosynthetic microorganisms. However, nano-photocatalysts could also induce oxidative stress and damage cells. In this paper, the mechanism and regulation strategy of cadmium sulfide nanoparticles（CdS NPs）on the growth of sulfate reducing bacteria and the sulfate reduction process were investigated. The results shows that the sulfate reduction efficiency could be increased by 6.43% through CdS NPs under light conditions. However, the growth of C09 was seriously inhibited by 55.00% due to the oxidative stress induced by CdS NPs on cells. The biomass and sulfate reduction efficiency could be enhanced by 6.84% and 5.85%, respectively, through external addition of humic acid (HA). At the same time, the mechanism of the CdS NPs strengthening the sulfate reduction process by sulfate bacteria was also studied. Which can provide important theoretical guidance and technical support for the development of microbial technology combined with extracellular electron transfer (EET) for the treatment of sulfate-containing wastewater.

Making protons tag along with electrons

Every living cell needs to get rid of leftover electrons when metabolism extracts energy through the oxidation of nutrients. Common soil microbes such as Geobacter sulfurreducens live in harsh environments that do not afford the luxury of soluble, ingestible electron acceptors like oxygen. Instead of resorting to fermentation, which requires the export of reduced compounds (e.g. ethanol or lactate derived from pyruvate) from the cell, these organisms have evolved a means to anaerobically respire by using nanowires to export electrons to extracellular acceptors in a process called extracellular electron transfer (EET) [ 1]. Since 2005, these nanowires were thought to be pili filaments [ 2]. But recent studies have revealed that nanowires are composed of multiheme cytochromes OmcS [ 3, 4] and OmcZ [ 5] whereas pili remain inside the cell during EET and are required for the secretion of nanowires [ 6]. However, how electrons are passed to these nanowires remains a mystery ( Figure 1A). Periplasmic cytochromes (Ppc) called PpcA-E could be doing the job, but only two of them (PpcA and PpcD) can couple electron/proton transfer — a necessary condition for energy generation. In a recent study, Salgueiro and co-workers selectively replaced an aromatic with an aliphatic residue to couple electron/proton transfer in PpcB and PpcE (Biochem. J. 2021, 478 (14): 2871–2887). This significant in vitro success of their protein engineering strategy may enable the optimization of bioenergetic machinery for bioenergy, biofuels, and bioelectronics applications.