Investigation of the potential of yeast strains for phytase biosynthesis in a two-step screening procedure

Research into phytase production is useful for improving the efficiency of animal production, reducing environmental impact, and contributing to the development of sustainable and efficient animal production systems. This study aims to investigate the potential of yeast strains for phytase biosynthesis in nutrient media. Phytase is a phosphomonoesterase (E.C 3.1.3.8) catalyzing in a ladder-like manner the dephosphorylation of phytic acid and its salts, with various resulting myo-inositol phosphates and phosphoric acid. Yeasts of the genera Saccharomyces, Zygosaccharomyces, Candida, and Pichia were evaluated in a two-step screening procedure for phytase production. One hundred and eighteen strains were screened in the first stage, which was conducted on four types of solid culture media containing calcium phytate as the selected background. On PSM medium, many strains were found to form halos as early as the 24th hour of development. Several strains with significant potential for enzyme production were evaluated in the second step of the screening. It was conducted in a liquid culture medium. In conclusion, the strain C. melibiosica 2491 was selected for further studies when cultured in a YPglu culture medium. Further research will focus on finding suitable conditions that increase the biosynthesis of the enzyme, which is of significant technological and practical interest for animal nutrition.

Improved membrane permeability with cetyltrimethylammonium bromide (CTAB) addition for enhanced bidirectional transport of substrate and electron shuttles

The effects of membrane permeability on extracellular electron transfer (EET) and performance of microbial fuel cell (MFC) need to be explored. In this work, cetyltrimethylammonium bromide (CTAB) was chosen to enhance the current generation and bidirectional transport of substrate and electron shuttles by tailoring the cell membrane permeability. Specifically, the peak currents of biofilms treated with CTAB especially at 200 μM were obviously higher than the control biofilm with no CTAB, and the riboflavin mediated electron transfer was promoted prominently. Biomass and viability analyses showed that an appropriate concentration of CTAB had almost no adverse effect on the cell viability of biofilm and could increase the biomass of biofilm. Measurements of the extracellular activity of alkaline phosphatase and UV-vis absorption confirmed the increased membrane permeability and the promoted efficiency of substrates transported into cells. This contribution paves the key step for facilitating EET process by adjusting membrane permeability through CTAB or other surfactants addition.

Gram-positive bacteria covered bioanode in a membrane-electrode assembly for use in bioelectrochemical systems

A novel strain of Gram-positive bacteria Paenibacillus profundus YoMME was recognized by sequencing of 16S rRNA gene and after that tested for exoelectrogenicity for the first time. It was found that at an applied potential of -0.195 V (vs. SHE) the bacteria are capable of generating electricity and forming electroactive biofilms for 3-4 days. A tendency for the decrease in double-layer capacitance and the increase in the charge transfer resistance during the maturation of the biofilm was established. The formed bioanodes were used as a part of a membrane-electrode assembly (MEA) together with a selected cathode (E-Tek) and a separator (Zirfon). The applicability of MEA with the bioanode was tested by operating a newly designed bioelectrochemical system in a microbial fuel cell (MFC) or microbial electrolysis cell (MEC) mode. A current density of 200 mA m-2 was generated by the MFC after the improvement of the cathodic reaction through facilitated air access. The Coulombic efficiency in different MFC runs ranged from 5.2 to 7.4%. It was also determined that 0.65 V applied cell voltage is appropriate for the operation of the cell in the electrolysis mode, during which a current density of 2-3 Am-2 was reached. This, along with the evolved gas on the cathode, shows that as an anodic biocatalyst P. profundus YoMME assists the electrolysis processes at a significantly lower voltage than the theoretical one (1.23 V) for water decomposition. The hydrogen production rate varied between 0.5 and 0.7 m3/m3d and the cathodic hydrogen recovery ranged from 49.5 to 61.5 %. The estimated energy efficiency based on the electricity input exceeds 100 %, which indicates that additional energy is being gained from the biotic oxidation of the available organics.

Fungal-mediated electrochemical system: Prospects, applications and challenges

Microbial fuel cells (MFCs) that generate bioelectricity from biodegradable waste have received considerable attention from biologists. Fungi play a significant role as both anodic and cathodic catalysts in MFCs. Saccharomyces cerevisiae is a fungus with an ability to transfer electrons through mediators such as methylene blue (MB), neutral red (NR) or even without a mediator. This unique role of fungal cells in exocellular electron transfer (EET) and their interactions with electrodes hold a lot of promise in areas such as wastewater treatment where yeast cell-based MFCs can be used. The present article highlights the physico-chemical factors affecting the performance of fungal-mediated MFCs in terms of power output and degradation of organic pollutants, along with the challenges associated with fungal MFCs. In addition, to this comparative assessment of fungal-mediated bio-electrochemical systems, their development, possible applications and potential challenges are also discussed.

Recent trends in upgrading the performance of yeast as electrode biocatalyst in microbial fuel cells

Microbial fuel cell (MFC) is an optimistic fuel cell technology that applies microorganism's biochemical catalytic activities in consuming organic substrate and produce electricity. In the past, several researchers have reported power generation from Saccharomyces cerevisiae, but nowadays, most of the studies are centred around bacterial biofilms (prokaryotes) as anode biocatalyst. Yeast (a eukaryote) has also been applied as a biocatalyst in MFCs as they are non-pathogenic, easy to handle and tolerant to various environmental conditions. Yeast strains such as Arxula adeninvorans, Candida melibiosica, Hansenula polymorpha, Hansenula anomala, Kluyveromyces marxianus and Saccharomyces cerevisiae have been utilized in MFCs. This review summarizes the application of yeast as an anode biocatalyst together with a discussion on the mechanism of electron transfer from yeast cells to the anode and highlights the techniques applied in improving the efficiency of yeast-based MFCs. The recent challenges and benefits of utilizing yeast in MFCs have been also encapsulated in this review.

A novel application of simple submersible yeast-based microbial fuel cells as dissolved oxygen sensors in environmental waters

In this study, yeast microbial fuel cells (MFCs) were established as biosensors for in-situ monitoring of dissolved oxygen (DO) levels in environmental waters, with yeast and glucose substrates acting as biocatalyst and fuel, respectively. Diverse environmental factors, such as temperature, pH and conductivity, were considered. The sensor performance was first tested with distilled water with different DO levels ranging from 0 mg/L to 8 mg/L and an external resistance of 1000 Ω. The relationship between DO and current density was non-linear (exponential). This MFC capability was further explored under different environmental conditions (pH, temperature and conductivity), and the current density produced was within the range of 0.14-34.88 mA/m², which increased with elevated DO concentration. The resulting regression was y = 1.3051e^0.3548x, with a regression coefficient (R²) = 0.71, indicating that the MFC-based DO meter was susceptible to interference. When used in environmental water samples, DO measurements using MFC resulted in errors ranging from 6.25 % to 15.15 % when compared with commercial DO meters. The simple yeast-based MFC sensors demonstrate promising prospects for future monitoring in a variety of areas, including developing countries and remote locations.

Potential of Zymomonas mobilis as an electricity producer in ethanol production

BACKGROUND

Microbial fuel cell (MFC) convokes microorganism to convert biomass into electricity. However, most well-known electrogenic strains cannot directly use glucose to produce valuable products. Zymomonas mobilis, a promising bacterium for ethanol production, owns special Entner-Doudoroff pathway with less ATP and biomass produced and the low-energy coupling respiration, making Z. mobilis a potential exoelectrogen.

RESULTS

A glucose-consuming MFC is constructed by inoculating Z. mobilis. The electricity with power density 2.0 mW/m² is derived from the difference of oxidation-reduction potential (ORP) between anode and cathode chambers. Besides, two-type electricity generation is observed as glucose-independent process and glucose-dependent process. For the sake of enhancing MFC efficiency, extracellular and intracellular strategies are implemented. Biofilm removal and addition of c-type cytochrome benefit electricity performance and Tween 80 accelerates the electricity generation. Perturbation of cellular redox balance compromises the electricity output, indicating that redox homeostasis is the principal requirement to reach ideal voltage.

CONCLUSION

This study identifies potential feature of electricity activity for Z. mobilis and provides multiple strategies to enhance the electricity output. Therefore, additional electricity generation will benefit the techno-economic viability of the commercial bulk production for biochemicals or biofuels in an efficient and environmentally sustainable manner.

Triclosan Removal in Microbial Fuel Cell: The Contribution of Adsorption and Bioelectricity Generation

The occurrence of Triclosan (TCS) in natural aquatic systems has been drawing increasing attention due to its endocrine-disruption effects as well as for the development of antibiotic resistances. Wastewater discharge is the main source of water contamination by TCS. In this study, the removal of TCS in microbial fuel cells (MFCs) was carefully investigated. A 94% removal of TCS was observed with 60 mV electricity generation as well as a slight drop in pH. In addition, we found that adsorption also contributed to the removal of TCS in aqueous solution and 21.73% and 19.92% of the total mass was adsorbed to the inner wall of the reactor and to the electrode, respectively. The results revealed that the attenuation of TCS depends on both biodegradation and physical adsorption in the anode chamber. Thus, the outcomes of our study provide a better understanding of the TCS removal mechanism in MFCs.

Enhanced phosphorus flux from overlying water to sediment in a bioelectrochemical system

This report proposed a novel technique for the regulation of phosphorus flux based on a bioelectrochemical system. In the simulated water system, a simple in situ sediment microbial fuel cell (SMFC) was constructed. SMFC voltage was increased with time until it was 0.23V. The redox potential of the sediment was increased from -220mV to -178mV during the process. Phosphorus concentration in the water system was decreased from 0.1mg/L to 0.01mg/L, compared with 0.09mg/L in the control. The installation of a SMFC produced an external current and internal circuit, which promoted the transfer of phosphate in overlying water to the sediment, enhanced the microbial oxidation of Fe(2+), and increased the formation of stable phosphorus in sediment. In conclusion, phosphorus flux from the overlying water to sediment was enhanced by SMFC, which has the potential to be used for eutrophication control of water bodies.

Mechanisms of electron transfer between a styrylquinolinium dye and yeast in biofuel cell

In the present study, the influence of the recently synthesized styrylquinolinium dye 4-{(E)-2-[4-(dimethylamino)naphthalen-1-yl]ethenyl}-1-methylquinolinium iodide (DANSQI) on the intracellular processes as well as the electrical outputs of Candida melibiosica 2491 yeast-based biofuel cell was investigated. The addition of nanomolar quantities of DANSQI to the yeast suspension results in an increase of the current outputs right after the startup of the biofuel cells, associated with an electrooxidation of the dye on the anode. After that, the formed cation radical of the dye penetrates the yeast cells, provoking a set of intracellular changes. Studies of the subcellular anolyte fractions show that 1μM dye increased the peroxisomal catalase activity 30-times (1.15±0.06Unit/mg protein) and over twice the mitochondrial cytochrome c oxidase activity (92±5Unit/mg protein). The results obtained by electrochemical and spectrophotometric analyses let to the supposition that the dye acts as subcellular shuttle, on account of its specific intramolecular charge transfer properties. The transition between its benzoid, quinolyl radical and ion forms and their putative role for the extracellular and intracellular charge transfer mechanisms are discussed.