Endogenously enhanced biosurfactant production promotes electricity generation from microbial fuel cells

Bioelectrochemical synthesis of rhamnolipids and energy production and its correlation with nitrogen in air-cathode microbial fuel cells

Microbial fuel cells (MFCs) have been recently proven to synthesise biosurfactants from waste products. In classic bioreactors, the efficiency of biosynthesis process can be controlled by the concentration of nitrogen content in the electrolyte. However, it was not known whether a similar control mechanism could be applied in current-generating conditions. In this work, the effect of nitrogen concentration on biosurfactant production from waste cooking oil was investigated. The concentration of NH4Cl in the electrolyte ranged from 0 to 1 g L-1. The maximum power density equal to 17.5 W m-3 was achieved at a concentration of 0.5 g L-1 (C/N = 2.32) and was accompanied by the highest surface tension decrease (to 54.6 mN m-1) and an emulsification activity index of 95.4%. Characterisation of the biosurfactants produced by the LC-MS/MS method showed the presence of eleven compounds belonging to the mono- and di-rhamnolipids group, most likely produced by P. aeruginosa, which was the most abundant (19.6%) in the community. Importantly, we have found a strong correlation (R = -0.96) of power and biosurfactant activity in response to C/N ratio. This study shows that nitrogen plays an important role in the current-generating metabolism of waste cooking oil. To the best of our knowledge, this is the first study where the nitrogen optimisation was investigated to improve the synthesis of biosurfactants and power generation in a bioelectrochemical system.

Enhancement of Electricity Production in Microbial Fuel Cells Using a Biosurfactant-Producing Co-Culture

Microbial fuel cells are bio-electrochemical devices that enable the conversion of chemical energy into bioelectricity. In this manuscript, the use of biosurfactants (Tween 80 and surfactin) and the effect of coculturing E. coli and L. plantarum were used to investigate the generation of bioelectricity coming from an H-type microbial fuel cell. In this setup, E. coli acts as an electron donor while L. plantarum acts as an in situ biosurfactant producer. It was observed that the use of exogenous surfactants enhanced electricity production compared to conventional E. coli cultures. The utilization of Tween 80 and surfactin increased the power generation from 204 µW m-2 to 506 µW m-2 and 577 µW m-2, respectively. Furthermore, co-culturing E. coli and L. plantarum also resulted in a higher power output compared to pure cultures (132.8% more when compared to using E. coli alone and 68.1% more when compared to using L. plantarum alone). Due to the presence of surfactants, the internal resistance of the cell was reduced. The experimental evidence collected here clearly indicates that the production of endogenous surfactants, as well as the addition of exogenous surfactants, will enhance MFC electricity production.

Construction and application of a new CRISPR/Cas12a system in Stenotrophomonas AGS-1 from aerobic granular sludge

Aerobic granular sludge (AGS) is a microbial aggregate with a biofilm structure. Thus, investigating AGS in the aspect of biofilm and microbial attachment at the genetic level would help to reveal the mechanism of granule biofilm formation. In this work, a two-plasmid clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated proteins (Cas)12a genome editing system was constructed to identify attachment genes for the first time in Stenotrophomonas AGS-1 from AGS. One plasmid contained a Cas12a cassette driven by an arabinose-inducible promoter, and another contained the specific crRNA and homologous arms (HAs). Acidaminococcus sp. Cas12a (AsCas12a) was adopted and proven to have mild toxicity (compared to Cas9) and strong cleavage activity for AGS-1. CRISPR/Cas12a-mediated rmlA knockout decreased attachment ability by 38.26%. Overexpression of rmlA in AGS-1 resulted in an increase of 30.33% in attachment ability. These results showed that the modulation of rmlA was an important factor for the biofilm formation of AGS-1. Moreover, two other genes (xanB and rpfF) were knocked out by CRISPR/Cas12a and identified as attachment-related genes in AGS-1. Also, this system could achieve point mutations. These data indicated that the CRISPR/Cas12a system could be an effective molecular platform for attachment gene function identification, which would be useful for the development of AGS in wastewater treatment.

Advances in mechanisms and engineering of electroactive biofilms

Electroactive biofilms (EABs) are electroactive microorganisms (EAMs) encased in conductive polymers that are secreted by EAMs and formed by the accumulation and cross-linking of extracellular polysaccharides, proteins, nucleic acids, lipids, and other components. EABs are present in the form of multicellular aggregates and play a crucial role in bioelectrochemical systems (BESs) for diverse applications, including biosensors, microbial fuel cells for renewable bioelectricity production and remediation of wastewaters, and microbial electrosynthesis of valuable chemicals. However, naturally occurred EABs are severely limited owing to their low electrical conductivity that seriously restrict the electron transfer efficiency and practical applications. In the recent decade, synthetic biology strategies have been adopted to elucidate the regulatory mechanisms of EABs, and to enhance the formation and electrical conductivity of EABs. Based on the formation of EABs and extracellular electron transfer (EET) mechanisms, the synthetic biology-based engineering strategies of EABs are summarized and reviewed as follows: (i) Engineering the structural components of EABs, including strengthening the synthesis and secretion of structural elements such as polysaccharides, eDNA, and structural proteins, to improve the formation of biofilms; (ii) Enhancing the electron transfer efficiency of EAMs, including optimizing the distribution of c-type cytochromes and conducting nanowire assembly to promote contact-based EET, and enhancing electron shuttles' biosynthesis and secretion to promote shuttle-mediated EET; (iii) Incorporating intracellular signaling molecules in EAMs, including quorum sensing systems, secondary messenger systems, and global regulatory systems, to increase the electron transfer flux in EABs. This review lays a foundation for the design and construction of EABs for diverse BES applications.

Moving towards the enhancement of extracellular electron transfer in electrogens

Electrogens are very common in nature and becoming a contemporary theme for research as they can be exploited for extracellular electron transfer. Extracellular electron transfer is the key mechanism behind bioelectricity generation and bioremediation of pollutants via microbes. Extracellular electron transfer mechanisms for electrogens other than Shewanella and Geobacter are less explored. An efficient extracellular electron transfer system is crucial for the sustainable future of bioelectrochemical systems. At present, the poor extracellular electron transfer efficiency remains a decisive factor in limiting the development of efficient bioelectrochemical systems. In this review article, the EET mechanisms in different electrogens (bacteria and yeast) have been focused. Apart from the well-known electron transfer mechanisms of Shewanella oneidensis and Geobacter metallireducens, a brief introduction of the EET pathway in Rhodopseudomonas palustris TIE-1, Sideroxydans lithotrophicus ES-1, Thermincola potens JR, Lysinibacillus varians GY32, Carboxydothermus ferrireducens, Enterococcus faecalis and Saccharomyces cerevisiae have been included. In addition to this, the article discusses the several approaches to anode modification and genetic engineering that may be used in order to increase the rate of extracellular electron transfer. In the side lines, this review includes the engagement of the electrogens for different applications followed by the future perspective of efficient extracellular electron transfer.

Insights into rhamnolipid amendment towards enhancing microbial electrochemical treatment of petroleum hydrocarbon contaminated soil

Environmental pollution by hydrophobic hydrocarbons is increasing, notably nowadays due to a large amount of industrial activity. Microbial electrochemical technologies (MET) are promising bio-based systems which can oxidize hydrophobic hydrocarbon pollutants and produce bioelectricity simultaneously. However, MET faces some issues in terms of soil remediation, including low mass transfer, limited electro-activity of anodes as electron acceptors, low bioavailability of hydrocarbons, and the limited activity of beneficial bacteria and inefficient electron transport. This study aims to investigate the role of the addition of rhamnolipid as an analyte solution to the MET to enhance the efficacy and concurrently solve the abovementioned issues. In this regard, a novel long chain of RL was produced by using low-cost carbon winery waste through non-pathogenic Burkholderia thailandensis E264 strains. Different doses of RL were tested, including 10, 50, and 100 mg/L. A maximum enhancement in the oxidation of hydrophobic hydrocarbons was found to be up to 72.5%, while the current density reached 9.5 Am-2 for the MET reactor having a dose of 100 mg/L. The biosurfactants induced a unique microbial enrichment associated with Geobacter, Desulfovibrio, Klebsiella, and Comamona on the anode surface, as well as Pseudomonas, Acinetobacter, and Franconibacter in soil MET, indicating the occurrence of a metabolic pathway in microbes working with the anode and soil bioelectrochemical remediation system. According to cyclic voltammetry analysis, redox peaks appeared, showing a minor shift in redox MET-biosurfactant compared to the bare MET system. Furthermore, the phytotoxicity of polluted soil to L. sativum seeds after and before MET remediation shows a decrease in phytotoxicity of 77.5% and 5% for MET-biosurfactant system and MET only, respectively. With MET as a tool, this study confirmed for the first time that novel long-chain RL produced from non-Pseudomonas bacteria could remarkably facilitate the degradation of petroleum hydrocarbon via extracellular electron transfer, which provides novel insights to understand the mechanisms of RL regulating petroleum hydrocarbon degradation.

Promoted microbial denitrification and carbon dioxide fixation via photogenerated electrons stored in novel core/shell memory photocatalysts in darkness

Excess nitrogen in water and greenhouse gases, especially atmospheric carbon dioxide (CO₂) from the rapid development of modern society have become an acute threat to the environment. Herein, novel core/shell structured g-C₃N₄@WO₃ memory photocatalyst was fabricated by coating g-C₃N₄ on the surface of WO₃ nanoparticles and applied in the simultaneous coupling of memory photocatalysts and microbial communities (SCMPMC) for the synergistic removal of microbial nitrate and CO₂ fixation in darkness. The results showed that ∼98.6% of nitrate was removed and ∼17.7% of CO₂ was fixed in darkness by microorganisms in the presence of g-C₃N₄@WO₃ memory photocatalyst within 48 h. Besides, the investigation of the mechanism evidenced that g-C₃N₄@WO₃ memory photocatalyst can promote electron transfer in the SCMPMC system. Moreover, key enzyme activities (i.e., NAR, NIR, CAT, and ETSA) were accelerated, indicating that the activities of enzymes within microorganisms could be remarkably enhanced by the continuous release of stored electrons by the g-C₃N₄@WO₃ memory photocatalyst in the dark. Furthermore, microbial community analysis revealed that the g-C₃N₄@WO₃ memory photocatalyst increased the relative abundance of denitrifiers (i.e., Acidobacterota, Actinobacteria, Chloroflexi, and Proteobacteria) and CO₂-assimilating microorganisms (i.e., Pseudomonas), in the treated communities compared with the original community in river sediment, demonstrating the positive effects of g-C₃N₄@WO₃ memory photocatalyst on river sediment microbial communities. The results in this study could shed new light on the establishment of promising synergistic microbial nitrate removal and CO₂ fixation methods and mechanisms in darkness.

A novel simultaneous coupling of memory photocatalysts and microbial communities for alternate removal of dimethyl phthalate and nitrate in water under light/dark cycles

Efficient and sustainable removal of both organic and inorganic pollutants from contaminated water is an important but difficult task. Here, a novel chemical-biological coupling concept, namely simultaneous coupling of memory photocatalysts and microbial communities (SCMPMC), is proposed for the first time that alternates the removal of organic and inorganic pollutants under successive light/dark cycles. We established this novel coupling system with WO₃/g-C₃N₄ memory photocatalysts and river sediment microbial communities, and applied it to alternately remove dimethyl phthalate (DMP) and nitrate under light/dark cycles. The performance of SCMPMC under the light/dark cycles (12/12 h) showed that ~84.90% of the DMP was removed mainly via robust photocatalytic oxidation during the light phase, and ~86.80% of the nitrate was removed via microbial reduction enhanced by photogenerated electrons stored in the WO₃/g-C₃N₄ memory photocatalysts during the dark phase within one cycle. The microbial communities were positively affected by adding WO₃/g-C₃N₄, as evidenced by increased enzyme activities, cellular antigen metabolism, and relative abundance of typical denitrifiers, including Proteobacteria and Bacteroidetes. These results will contribute to the development of promising decontamination methods and mechanisms to control water pollution driven by the natural day/night cycle.

Yeast-induced formation of graphene hydrogels anode for efficient xylose-fueled microbial fuel cells

Microbial fuel cells (MFCs) are of great interest due to their capability to directly convert organic compounds to electric energy. In particular, MFCs technology showed great potential to directly harness the energy from xylose in the form of bioelectricity and biohydrogen simultaneously. Herein, we report a yeast strain of Cystobasidium slooffiae JSUX1 enabled the reduction and assembly of graphene oxide (GO) nanosheets into three-dimensional reduced GO (3D rGO) hydrogels on the surface of carbon felt (CF) anode. The autonomously self-modified 3D rGO hydrogel anode entitled the yeast-based MFCs with two times enhancement on bioelectricity and biohydrogen production from xylose. Further analysis demonstrated that the 3D rGO hydrogel attracted more yeast cells and reduced the interfacial charge transfer resistance, which was the underlying mechanism for the improvement of MFCs performance. This work offers a new strategy to reinforce the performance of yeast-based MFCs and provides a new opportunity to efficiently harvest energy from xylose.

Recent advancements in microbial fuel cells: A review on its electron transfer mechanisms, microbial community, types of substrates and design for bio-electrochemical treatment

The development in urbanization, growth in industrialization and deficiency in crude oil wealth has made to focus more for the renewable and also sustainable spotless energy resources. In the past two decades, the concepts of microbial fuel cell have caught more considerations among the scientific societies for the probability of converting, organic waste materials into bio-energy using microorganisms catalyzed anode, and enzymatic/microbial/abiotic/biotic cathode electro-chemical reactions. The added benefit with MFCs technology for waste water treatment is numerous bio-centered processes are available such as sulfate removal, denitrification, nitrification, removal of chemical oxygen demand and biological oxygen demand and heavy metals removal can be performed in the same MFC designed systems. The various factors intricate in MFC concepts in the direction of bioenergy production consists of maximum coulombic efficiency, power density and also the rate of removal of chemical oxygen demand which calculates the efficacy of the MFC unit. Even though the efficacy of MFCs in bioenergy production was initially quietly low, therefore to overcome these issues few modifications are incorporated in design and components of the MFC units, thereby functioning of the MFC unit have improvised the rate of bioenergy production to a substantial level by this means empowering application of MFC technology in numerous sectors including carbon capture, bio-hydrogen production, bioremediation, biosensors, desalination, and wastewater treatment. The present article reviews about the microbial community, types of substrates and information about the several designs of MFCs in an endeavor to get the better of practical difficulties of the MFC technology.

Microbial extracellular electron transfer and strategies for engineering electroactive microorganisms

Electroactive microorganisms (EAMs) are ubiquitous in nature and have attracted considerable attention as they can be used for energy recovery and environmental remediation via their extracellular electron transfer (EET) capabilities. Although the EET mechanisms of Shewanella and Geobacter have been rigorously investigated and are well characterized, much less is known about the EET mechanisms of other microorganisms. For EAMs, efficient EET is crucial for the sustainable economic development of bioelectrochemical systems (BESs). Currently, the low efficiency of EET remains a key factor in limiting the development of BESs. In this review, we focus on the EET mechanisms of different microorganisms, (i.e., bacteria, fungi, and archaea). In addition, we describe in detail three engineering strategies for improving the EET ability of EAMs: (1) enhancing transmembrane electron transport via cytochrome protein channels; (2) accelerating electron transport via electron shuttle synthesis and transmission; and (3) promoting the microbe-electrode interface reaction via regulating biofilm formation. At the end of this review, we look to the future, with an emphasis on the cross-disciplinary integration of systems biology and synthetic biology to build high-performance EAM systems.

Recent advancements in the production of rhamnolipid biosurfactants by Pseudomonas aeruginosa

Rhamnolipid (RL) biosurfactant which is produced by Pseudomonas species is one of the most effective surface-active agents investigated in the literature. Over the years, many efforts have been made and an array of techniques has been developed for the isolation of RL produced strains as well as RL homolog characterization. Reports show that RL productivity by the best-known producer, Pseudomonas aeruginosa, is very diverse, from less than 1 gr/l to more than 200 g L-1. There are some major parameters that can affect RL productivity. These are culture conditions, medium composition, the mode of operation (batch, fed-batch and continuous), bioengineering/gene manipulation and finally extraction methods. The present paper seeks to provide a comprehensive overview on the production of rhamnolipid biosurfactant by different species of Pseudomonas bacteria. In addition, we have extensively reviewed their potential for possible future applications.

Genetic engineering for enhanced productivity in bioelectrochemical systems

A shift from petrochemical processes toward a bio-based economy is one of the most advocated developments for a sustainable future. To achieve this will require the biotechnological production of platform chemicals that can be further processed by chemical engineering. Bioelectrochemical systems (BESs) are a novel tool within the biotechnology field. In BESs, microbes serve as biocatalysts for the production of biofuels and value-added compounds, as well as for the production of electricity. Although the general feasibility of bioelectrochemical processes has been demonstrated in recent years, much research has been conducted to develop biocatalysts better suited to meet industrial demands. Initially, mainly natural exoelectrogenic organisms were investigated for their performance in BESs. Driven by possibilities of recent developments in genetic engineering and synthetic biology, the spectrum of microbial catalysts and their versatility (substrate and product range) have expanded significantly. Despite these developments, there is still a tremendous gap between currently achievable space-time yields and current densities on the one hand and the theoretical limits of BESs on the other. It will be necessary to move the performance of the biocatalysts closer to the theoretical possibilities in order to establish viable production routines. This review summarizes the status quo of engineering microbial biocatalysts for anode-applications with high space-time yields. Furthermore, we will address some of the theoretical limitations of these processes exemplarily and discuss which of the present strategies might be combined to achieve highly synergistic effects and, thus, meet industrial demands.

Global regulator engineering enhances bioelectricity generation in Pseudomonas aeruginosa-inoculated MFCs

The electricigens with high-electroactivity is essential for resolving the low electricity power output (EPT) of microbial fuel cells (MFCs). However, the manipulation by single functional genes shows limitation because electroactivity is a complex phenotype controlled by multiple genes. Herein, global regulator engineering (GRE) was developed to optimize the electroactivity of an isolated strain (Pseudomonas aeruginosa P3-A-11) using an exogenous global regulator IrrE (ionizing radiation resistance E linkage group) as an object. The GRE was implemented through in vitro random mutagenesis by error-prone PCR and in vivo high-through screening comprised of cultures color assay, PYO measurement and MFCs operation. Four mutants with higher electroactivity were obtained, among which, the mutant 11/M2-59 not only displayed the maximal power density, but also exhibited stronger salt tolerance, consequently showing good performance of MFCs in the presence of salt. Apart from the reduced internal resistance, the increase in phenazines amounts primarily contributed to EPT improvement, which was realized by enhancing the core biosynthesis pathway and affecting other pathways (such as central metabolism pathway, quorum sensing system, regulatory network). Notably, IrrE exerted its positive effect on electroactivity even without native regulators (such as PmpR and RpoS). In addition, the significant fluctuations in expression levels of stress-responsive genes mediated by GRE were closely associated with the enhanced salt tolerance. This work demonstrated that GRE was an effective approach for simultaneously optimizing multiple phenotypes (such as electroactivity and stress tolerance), and thus would provide more opportunities to create high-efficiency electricigens and further promoted the practical application of MFCs.

Biosurfactants and Synthetic Surfactants in Bioelectrochemical Systems: A Mini-Review

Bioelectrochemical systems (BESs) are ruled by a complex combination of biological and abiotic factors. The interplay of these factors determines the overall efficiency of BES in generating electricity and treating waste. The recent progress in bioelectrochemistry of BESs and electrobiotechnology exposed an important group of compounds, which have a significant contribution to operation and efficiency: surface-active agents, also termed surfactants. Implementation of the interfacial science led to determining several effects of synthetic and natural surfactants on BESs operation. In high pH, these amphiphilic compounds prevent the cathode electrodes from biodeterioration. Through solubilization, their presence leads to increased catabolism of hydrophobic compounds. They interfere with the surface of the electrodes leading to improved biofilm formation, while affecting its microarchitecture and composition. Furthermore, they may act as quorum sensing activators and induce the synthesis of electron shuttles produced by electroactive bacteria. On the other hand, the bioelectrochemical activity can be tailored for new, improved biosurfactant production processes. Herein, the most recent knowledge on the effects of these promising compounds in BESs is discussed.

Redox mediators as charge agents for changing electrochemical reactions

This review provides a comprehensive discussion toward understanding the effects of RMs in electrochemical systems, underlying redox mechanisms, and reaction kinetics both experimentally and theoretically.

Enhanced Rhodococcus pyridinivorans HR-1 anode performance by adding trehalose lipid in microbial fuel cell

In this study, a trehalose lipid was added to a Rhodococcus pyridinivorans-inoculated MFC to improve the power output by enhancing electron transfer. Upon trehalose lipid additions of different concentrate from 0 to 20 mg/L, the maximum power density increased from 54.7 mW/m² to 324.4 mW/m² (5.93 times) while the corresponding current density was 3.66 times increased from 0.35 A/m² to 1.28 A/m². Cyclic voltammetry analysis revealed that the addition of trehalose lipid increased the electron transfer performance, while electrochemical impedance spectroscopy results proved a decrease in internal resistance. It was demonstrated that adding bio-surfactant in MFC was a novel way to enhance power output performance.

Microbial production of rhamnolipids: opportunities, challenges and strategies

Rhamnolipids are a class of biosurfactants which contain rhamnose as the sugar moiety linked to β-hydroxylated fatty acid chains. Rhamnolipids can be widely applied in many industries including petroleum, food, agriculture and bioremediation etc. Pseudomonas aeruginosa is still the most competent producer of rhamnolipids, but its pathogenicity may cause safety and health concerns during large-scale production and applications. Therefore, extensive studies have been carried out to explore safe and economical methods to produce rhamnolipids. Various metabolic engineering efforts have also been applied to either P. aeruginosa for improving its rhamnolipid production and diminishing its pathogenicity, or to other non-pathogenic strains by introducing the key genes for safe production of rhamnolipids. The three key enzymes for rhamnolipid biosynthesis, RhlA, RhlB and RhlC, are found almost exclusively in Pseudomonas sp. and Burkholderia sp., but have been successfully expressed in several non-pathogenic host bacteria to produce rhamnolipids in large scales. The composition of mono- and di-rhamnolipids can also be modified through altering the expression levels of RhlB and RhlC. In addition, cell-free rhamnolipid synthesis by using the key enzymes and precursors from non-pathogenic sources is thought to not only eliminate pathogenic effects and simplify the downstream purification processes, but also to circumvent the complexity of quorum sensing system that regulates rhamnolipid biosynthesis. The pathogenicity of P. aeruginosa can also be reduced or eliminated through in vivo or in vitro enzymatic degradation of the toxins such as pyocyanin during rhamnolipid production. The rhamnolipid production cost can also be significantly reduced if rhamnolipid purification step can be bypassed, such as utilizing the fermentation broth or the rhamnolipid-producing strains directly in the industrial applications of rhamnolipids.

Effects of Fe, Ni, and Fe/Ni metallic nanoparticles on power production and biosurfactant production from used vegetable oil in the anode chamber of a microbial fuel cell

In this study, metallic nanoparticles (Fe, Ni, and Fe/Ni) were used as cathode catalysts to enhance power production and to improve the anode performance of a two-chambered microbial fuel cell (MFC). The metallic nanoparticles were rod-shaped and produced by the precipitation/co-precipitation method. A biosurfactant was produced in the anode chamber of the MFC from used vegetable oil by the bacteria Serratia sp. Overall cell voltage, power density, bacterial growth, and biosurfactant production were studied by applying different types of metallic nanoparticles to the cathode electrode. The influence of various types of nanoparticles on the impedance of the MFC was also investigated by electrochemical impedance spectroscopy (EIS), including analyses of anode impedance, cathode impedance, anode solution resistance, cathode solution resistance, and membrane resistance. The nanoparticles improved MFC performance in the following order: Fe>Ni>Fe/Ni. The addition of 1.5mg/cm² Fe nanoparticles to the cathode surface enhanced power production by over 500% to 66.4mW/m³, promoted bacterial growth and biosurfactant production in the anode solution by 132.5% and 32.0%, respectively, and reduced anode impedance, cathode impedance, and membrane resistance by 26.8%, 81.6%, and 33.8% to 159.00Ω, 7.69Ω, and 261.09Ω, respectively. For the first time, biosurfacant production in the anode chamber of the MFC was promoted by using the metallic nanoparticles as cathode catalysts. By improving the cathode properties, this study showed a new way to manipulated the performance of the anode chamber of the MFC.

Polarity inversion of bioanode for biocathodic reduction of aromatic pollutants

The enrichment of specific pollutant-reducing consortium is usually required prior to the startup of biocathode bioelectrochemical system (BES) and the whole process is time consuming. To rapidly establish a non-specific functional biocathode, direct polar inversion from bioanode to biocathode is proposed in this study. Based on the diverse reductases and electron transfer related proteins of anode-respiring bacteria (ARB), the acclimated electrochemically active biofilm (EAB) may catalyze reduction of different aromatic pollutants. Within approximately 12 d, the acclimated bioanodes were directly employed as biocathodes for nitroaromatic nitrobenzene (NB) and azo dye acid orange 7 (AO7) reduction. Our results indicated that the established biocathode significantly accelerated the reduction of NB to aniline (AN) and AO7 to discolored products compared with the abiotic cathode and open circuit controls. Several microbes possessing capabilities of nitroaromatic/azo dye reduction and bidirectional electron transfer were maintained or enriched in the biocathode communities. Cyclic voltammetry highlighted the decreased over-potentials and enhanced electron transfer of biocathode as well as demonstrated the ARB Geobacter containing cytochrome c involved in the backward electron transfer from electrode to NB. This study offers new insights into the rapid establishment and modularization of functional biocathodes for the potential treatment of complicated electron acceptors-coexisting wastewaters.

Performance improvement of microbial fuel cell (MFC) using suitable electrode and Bioengineered organisms: A review

There is an urgent need to find an environment friendly and sustainable technology for alternative energy due to rapid depletion of fossil fuel and industrialization. Microbial Fuel Cells (MFCs) have operational and functional advantages over the current technologies for energy generation from organic matter as it directly converts electricity from substrate at ambient temperature. However, MFCs are still unsuitable for high energy demands due to practical limitations. The overall performance of an MFC depends on microorganism, appropriate electrode materials, suitable MFC designs, and optimizing process parameters which would accelerate commercialization of this technology in near future. In this review, we put forth the recent developments on microorganism and electrode material that are critical for the generation of bioelectricity generation. This would give a comprehensive insight into the characteristics, options, modifications, and evaluations of these parameters and their effects on process development of MFCs.

Utilization of mango kernel oil for the rhamnolipid production by Pseudomonas aeruginosa DR1 towards its application as biocontrol agent

Mango kernel oil (MKO), derived from mango kernels, considered to be one of the highly generated agro-industrial waste, is assessed for its use as substrate for sustainable production of rhamnolipids. In the present study, MKO in combination with glucose gave maximum rhamnolipid yield of 2.8g/l which reduced the surface tension of water from 72 to 30mN/m, holding a CMC of 80mg/l and also showed high emulsification activity (73%) with diesel. Cell free broth was found to be stable even at high temperature (autoclaved at 121°C for 30min), pH value (up to pH 12) and salinity (up to 20% NaCl). The LC-MS data showed mono-rhamnolipid to be predominant congener followed by di-rhamnolipid in presence of MKO. Whereas, di-rhamnolipid was abundant when a combination of MKO with glucose was used. The produced rhamnolipid mixture showed good antifungal activity against various phytopathogens.