Effect of nanosecond pulsed electric field treatment on cell proliferation of microalgae

A review on point mutations via proton transfer in DNA base pairs in the absence and presence of electric fields

This comprehensive review focuses on spontaneous mutations that may occur during DNA replication, the fundamental process responsible for transferring genetic information. In 1963, Löwdin postulated that these mutations are primarily a result of proton transfer reactions within the hydrogen-bonded DNA base pairs. The single and double proton transfer reactions within the base pairs in DNA result in zwitterions and rare tautomers, respectively. For persistent mutations, these products must be generated at high rates and should be thermodynamically stable. This review covers the proton transfer reactions studied experimentally and computationally. The review also examines the influence of externally applied electric fields on the thermodynamics and kinetics of proton transfer reactions within DNA base pairs, and their biological implications.

Enhancing microalgal biomass production in lab-scale raceway ponds through innovative computational fluid dynamics-based electrode deflectors

The design of novel electrode deflector structures (EDSs) introduced a promising strategy for enhancing raceway ponds performance, increasing carbon fixation, and improving microalgal biomass accumulation. The computational fluid dynamics, based flow field principles, proved that the potency of arc-shaped electrode deflector structures (A-EDS) and spiral electrode deflector structures (S-EDS) were optimal. These configurations yielded superior culture effects, notably reducing dead zones by 9.1% and 11.7%, while elevating biomass increments of 14.7% and 11.5% compared to the control, respectively. In comparison to scenarios without electrostatic field application, the A-EDS group demonstrated pronounced post-stimulation growth, exhibiting an additional biomass increase of 11.2%, coupled with a remarkable 23.6% surge in CO2 fixation rate and mixing time reduction by 14.7%. A-EDS and S-EDS, combined with strategic electric field integration, provided a theoretical basis for promoting microalgal biomass production and enhancing carbon fixation in a raceway pond environment to similar production practices.

Effective removing of rotifer contamination in microalgal lab-scale raceway ponds by light-induced phototaxis coupled with high-voltage pulse electroshock

Rotifer reproduction control in open microalgae cultivation systems poses a significant challenge for large-scale industries. Conventional methods, such as electric, meshing, and chemical techniques, are often expensive, ineffective, and may have adverse environmental-health impacts. This study investigated a promising control technique through light-induced phototaxis to concentrate rotifers in a specific spot, where they were electroshocked by local-limited exposure dose. The results showed that the rotifers had the most pronounced positive and negative phototropism with phototaxis rates of 66.7 % and -78.8 %, respectively, at blue-light irradiation of 30 µmol∙m-2∙s-1 and red-light irradiation of 22.5 µmol∙m-2∙s-1 for 20 min. The most effective electroshock configuration employed 1200 V/cm for 15 min with a 1-second cycle time and a 10 % duty cycle, resulting in a 75.0 % rotifer removal rate without impacting microalgae growth. The combination of the two light beams could effectively lead rotifers to designated areas where they were electrocuted successfully.

Relationships of pulsed frequency and anammox bacteria growth rate, at low temperatures

This study explored pulsed frequency that could enhance the anammox bacteria growth rate and TN removal rate at low temperatures (16 ± 1°C). The results showed that the growth rate of anammox bacteria in R1 (1000 Hz) was significantly higher than in R2 (30 Hz) and R3 (106Hz). The relative abundance values of anammox bacteria R1 were higher by 52.21% and 172.41% than R2 and R3, while that of MLSS were as high as 241.07% and 471.36% than R2 and R3, with the nitrogen loading rate was 6.84 kg-N/m³/d. Besides, the dynamics also showed that the specific anammox activity (SAA) and the cellular yield of R1 were higher than R2 and R3. The intermediate frequency could enhance the cell division by stimulating the anammoxosome and reduce the ionic hydration layer to accelerate the ion migration rate, further improving the number of anammox bacteria even at low temperatures. The pulsed frequency could enhance the anammox growth rate and the doubling time is just 5 d.

Changes in Gene Expression After Exposing Arabidopsis thaliana Plants to Nanosecond High Amplitude Electromagnetic Field Pulses

The biological effects of exposure to electromagnetic fields due to wireless technologies and connected devices are a subject of particular research interest. Ultrashort high-amplitude electromagnetic field pulses delivered to biological samples using immersed electrodes in a dedicated cuvette have widely demonstrated their effectiveness in triggering several cell responses including increased cytosolic calcium concentration and reactive oxygen species (ROS) production. In contrast, the effects of these pulses are poorly documented when electromagnetic pulses are delivered through an antenna. Here we exposed Arabidopsis thaliana plants to 30,000 pulses (237  kV m-1 , 280 ps rise-time, duration of 500 ps) emitted through a Koshelev antenna and monitored the consequences of electromagnetic fields exposure on the expression levels of several key genes involved in calcium metabolism, signal transduction, ROS, and energy status. We found that this treatment was mostly unable to trigger significant changes in the messenger RNA accumulation of calmodulin, Zinc-Finger protein ZAT12, NADPH oxidase/respiratory burst oxidase homolog (RBOH) isoforms D and F, Catalase (CAT2), glutamate-cystein ligase (GSH1), glutathione synthetase (GSH2), Sucrose non-fermenting-related Kinase 1 (SnRK1) and Target of rapamycin (TOR). In contrast, Ascorbate peroxidases APX-1 and APX-6 were significantly induced 3 h after the exposure. These results suggest that this treatment, although quite strong in amplitude, is mostly ineffective in inducing biological effects at the transcriptional level when delivered by an antenna. © 2023 The Authors. Bioelectromagnetics published by Wiley Periodicals LLC on behalf of Bioelectromagnetics Society.

Low-Intensity Nanosecond Pulsed Electric Field Accelerates Osteogenic Transformation of Human Dermal Fibroblasts by Enhancing Cell Pluripotency

Autologous human fibroblasts have the potential to differentiate into the osteogenic lineage under specific conditions and can be utilized for bone regeneration. However, their efficiency is currently unsatisfactory. Recently, low-intensity nanosecond pulsed electric field (nsPEF) stimulation has been demonstrated to enhance cell pluripotency by activating epigenetic regulatory pathways. In this study, human dermal fibroblasts were exposed to different intensities of nsPEF to assess whether these exposures resulted in changes in proliferation rate, calcium salt deposition, and expression of differentiation-related markers in different experimental groups. The results showed a significant increase in cell proliferation, pluripotency, bone marker expression, and osteogenic differentiation efficiency when stimulating cells with 5 kV/cm of nsPEF. However, cell proliferation and differentiation significantly decreased at 25 kV/cm. Additionally, the proliferation and efficiency of osteogenic differentiation were reduced when the nsPEF intensity was increased to 50 kV/cm. Treatment with a 5 kV/cm of nsPEF led to increased and concentrated expression of Yes-Associated Protein (YAP) in the nucleus. These observations suggest that human dermal fibroblasts possess a heightened potential to differentiate into osteogenic cells when activated with nsPEF at 5 kV/cm. Consequently, the nsPEF strengthening strategy shows promise for fibroblast-based tissue-engineered bone repair research.

Enhanced Cell Viability and Migration of Primary Bovine Annular Fibrosus Fibroblast-like Cells Induced by Microsecond Pulsed Electric Field Exposure

This study is the first to report the enhancement of cell migration and proliferation induced by in vitro microsecond pulsed electric field (μsPEF) exposure of primary bovine annulus fibrosus (AF) fibroblast-like cells. AF primary cells isolated from fresh bovine intervertebral disks (IVDs) are exposed to 10 and 100 μsPEFs with different numbers of pulses and applied electric field strengths. The results indicate that 10 μs-duration pulses induce reversible electroporation, while 100 μs pulses induce irreversible electroporation of the cells. Additionally, μsPEF exposure increased AF cell proliferation up to 150% while increasing the average migration speed by 0.08 μm/min over 24 h. The findings suggest that the effects of PEF exposure on cells are multifactorial-depending on the duration, intensity, and number of pulses used in the stimulation. This highlights the importance of optimizing the μsPEF parameters for specific cell types and applications. For instance, if the goal is to induce cell death for cancer treatment, then high numbers of pulses can be used to maximize the lethal effects. On the other hand, if the goal is to enhance cell proliferation, a combination of the number of pulses and the applied electric field strength can be tuned to achieve the desired outcome. The information gleaned from this study can be applied in the future to in vitro cell culture expansion and tissue regeneration.

Protein-Mediated Electroporation in a Cardiac Voltage-Sensing Domain Due to an nsPEF Stimulus

This study takes a step in understanding the physiological implications of the nanosecond pulsed electric field (nsPEF) by integrating molecular dynamics simulations and machine learning techniques. nsPEF, a state-of-the-art technology, uses high-voltage electric field pulses with a nanosecond duration to modulate cellular activity. This investigation reveals a relatively new and underexplored phenomenon: protein-mediated electroporation. Our research focused on the voltage-sensing domain (VSD) of the NaV1.5 sodium cardiac channel in response to nsPEF stimulation. We scrutinized the VSD structures that form pores and thereby contribute to the physical chemistry that governs the defibrillation effect of nsPEF. To do so, we conducted a comprehensive analysis involving the clustering of 142 replicas simulated for 50 ns under nsPEF stimuli. We subsequently pinpointed the representative structures of each cluster and computed the free energy between them. We find that the selected VSD of NaV1.5 forms pores under nsPEF stimulation, but in a way that significant differs from the traditional VSD opening. This study not only extends our understanding of nsPEF and its interaction with protein channels but also adds a new effect to further study.

Nanosecond pulsed electric field (nsPEF) and vaccines: a novel technique for the inactivation of SARS-CoV-2 and other viruses?

Since the beginning of 2020, worldwide attention has been being focussed on SARS-CoV-2, the second strain of the severe acute respiratory syndrome virus. Although advances in vaccine technology have been made, particularly considering the advent of mRNA vaccines, up to date, no single antigen design can ensure optimal immune response. Therefore, new technologies must be tested as to their ability to further improve vaccines. Nanosecond Pulsed Electric Field (nsPEF) is one such method showing great promise in different biomedical and industrial fields, including the fight against COVID-19. Of note, available research shows that nsPEF directly damages the cell's DNA, so it is critical to determine if this technology could be able to fragment either viral DNA or RNA so as to be used as a novel technology to produce inactivated pathogenic agents that may, in turn, be used for the production of vaccines. Considering the available evidence, we propose that nsPEF may be used to produce inactivated SARS-CoV-2 viruses that may in turn be used to produce novel vaccines, as another tool to address 20 the current COVID-19 pandemic.Key MessagesViral inactivation by using pulsed electric fields in the nanosecond frequency.DNA fragmentation by a Nanosecond Pulsed Electric Field (nsPEF).Opportunity to apply new technologies in vaccine development.

Nanosecond Pulsed Electric Field (nsPEF): Opening the Biotechnological Pandora’s Box

Nanosecond Pulsed Electric Field (nsPEF) is an electrostimulation technique first developed in 1995; nsPEF requires the delivery of a series of pulses of high electric fields in the order of nanoseconds into biological tissues or cells. They primary effects in cells is the formation of membrane nanopores and the activation of ionic channels, leading to an incremental increase in cytoplasmic Ca2+ concentration, which triggers a signaling cascade producing a variety of effects: from apoptosis up to cell differentiation and proliferation. Further, nsPEF may affect organelles, making nsPEF a unique tool to manipulate and study cells. This technique is exploited in a broad spectrum of applications, such as: sterilization in the food industry, seed germination, anti-parasitic effects, wound healing, increased immune response, activation of neurons and myocites, cell proliferation, cellular phenotype manipulation, modulation of gene expression, and as a novel cancer treatment. This review thoroughly explores both nsPEF’s history and applications, with emphasis on the cellular effects from a biophysics perspective, highlighting the role of ionic channels as a mechanistic driver of the increase in cytoplasmic Ca2+ concentration.

What is the future of electrical impedance spectroscopy in flow cytometry?

More than 20 years ago, electrical impedance spectroscopy (EIS) was proposed as a potential characterization method for flow cytometry. As the setup is comparably simple and the method is label-free, EIS has attracted considerable interest from the research community as a potential alternative to standard optical methods, such as fluorescence-activated cell sorting (FACS). However, until today, FACS remains by and large the laboratory standard with highly developed capabilities and broad use in research and clinical settings. Nevertheless, can EIS still provide a complement or alternative to FACS in specific applications? In this Perspective, we will give an overview of the current state of the art of EIS in terms of technologies and capabilities. We will then describe recent advances in EIS-based flow cytometry, compare the performance to that of FACS methods, and discuss potential prospects of EIS in flow cytometry.

Exploring the Conformational Changes Induced by Nanosecond Pulsed Electric Fields on the Voltage Sensing Domain of a Ca2+ Channel

Nanosecond Pulsed Electric Field (nsPEF or Nano Pulsed Stimulation, NPS) is a technology that delivers a series of pulses of high-voltage electric fields during a short period of time, in the order of nanoseconds. The main consequence of nsPEF upon cells is the formation of nanopores, which is followed by the gating of ionic channels. Literature is conclusive in that the physiological mechanisms governing ion channel gating occur in the order of milliseconds. Hence, understanding how these channels can be activated by a nsPEF would be an important step in order to conciliate fundamental biophysical knowledge with improved nsPEF applications. To get insights on both the kinetics and thermodynamics of ion channel gating induced by nsPEF, in this work, we simulated the Voltage Sensing Domain (VSD) of a voltage-gated Ca2+ channel, inserted in phospholipidic membranes with different concentrations of cholesterol. We studied the conformational changes of the VSD under a nsPEF mimicked by the application of a continuous electric field lasting 50 ns with different intensities as an approach to reveal novel mechanisms leading to ion channel gating in such short timescales. Our results show that using a membrane with high cholesterol content, under an nsPEF of 50 ns and E→ = 0.2 V/nm, the VSD undergoes major conformational changes. As a whole, our work supports the notion that membrane composition may act as an allosteric regulator, specifically cholesterol content, which is fundamental for the response of the VSD to an external electric field. Moreover, changes on the VSD structure suggest that the gating of voltage-gated Ca2+ channels by a nsPEF may be due to major conformational changes elicited in response to the external electric field. Finally, the VSD/cholesterol-bilayer under an nsPEF of 50 ns and E→ = 0.2 V/nm elicits a pore formation across the VSD suggesting a new non-reported effect of nsPEF into cells, which can be called a “protein mediated electroporation”.

Improving the lipid extraction yield from Chlorella based on the controllable electroporation of cell membrane by pulsed electric field

In order to solve the increasingly serious problems of energy and environment, microalgae are used as a raw material for extracting lipids to produce biodiesel. Prior to the extraction of lipids, microalgae were treated with high-voltage pulsed electric field (PEF) to break the cell membrane. It was found that the lipid extraction yield depends on the electric field strength (E) and the specific energy input (Wsp), and has a certain relationship with the cell disintegration rate of Chlorella. The perforation degree of the Chlorella's cell membrane by PEF treatment is controllable, moderate perforation can be ensured by controlling the power parameters. PEF treatment significantly improved the extraction yield of lipids. Compared with the test samples without PEF treatment, PEF treatment increased the lipid extraction yields by up to 166.67%. However, an excessively high voltage will cause the quality of the extracted biodiesel to decrease.

Enhancing single-cell bioconversion efficiency by harnessing nanosecond pulsed electric field processing

Nanosecond pulsed electric field (nsPEF) processing is gaining momentum as a physical means for single-cell bioconversion efficiency enhancement. The technology allows biomass yields per substrate (Y_X/S) to be leveraged and poses a viable option for stimulating intracellular compound production. NsPEF processing thus resonates with myriad domains spanning the pharmaceutical and medical sectors, as well as food and feed production. The exact working mechanisms underlying nsPEF-based enhancement of bioconversion efficiency, however, remain elusive, and a better understanding would be pivotal for leveraging process control to broaden the application of nsPEF and scale-up industrial implementation. To bridge this gap, the study provides the electrotechnological and metabolic fundamentals of nsPEF processing in the bio-based domain to enable a critical evaluation of pathways underlying the enhancement of single-cell bioconversion efficiency. Evidence suggests that treating cells during the rapid proliferating and thus the early to mid-exponential state of cellular growth is critical to promoting bioconversion efficiency. A combined effect of transient intracellular and sublethal stress induction and effects caused on the plasma membrane level result in an enhancement of cellular bioconversion efficiency. Congruency exists regarding the involvement of transient cytosolic Ca²⁺ hubs in nsPEF treatment responses, as well as that of reactive oxygen species formation culminating in the onset of cellular response pathways. A distinct assignment of single effects and their contributions to enhancing bioconversion efficiency, however, remains challenging. Current applications of nsPEF processing comprise microalgae, bacteria, and yeast biorefineries, but these endeavors are in their infancies with limitations associated with a lack of understanding of the underlying treatment mechanisms, an incomplete reporting, insufficient characterization, and control of processing parameters. The study aids in fostering the upsurge of nsPEF applications in the bio-based domain by providing a basis to gain a better understanding of cellular mechanisms underlying an nsPEF-based enhancement of cellular bioconversion efficiency and suggests best practice guidelines for nsPEF documentation for improved knowledge transfer. Better understanding and reporting of processes parameters and consequently improved process control could foster industrial-scale nsPEF realization and ultimately aid in perpetuating nsPEF applicability within the bio-based domain.

The influence of external electric fields on proton transfer tautomerism in the guanine-cytosine base pair

The Watson-Crick base pair proton transfer tautomers would be widely considered as a source of spontaneous mutations in DNA replication if not for their short lifetimes and thermodynamic instability. This work investigates the effects external electric fields have on the stability of the guanine-cytosine proton transfer tautomers within a realistic strand of aqueous DNA using a combination of ensemble-based classical molecular dynamics (MD) coupled to quantum mechanics/molecular mechanics (QM/MM). Performing an ensemble of calculations accounts for the stochastic aspects of the simulations while allowing for easier identification of systematic errors. The methodology applied in this work has previously been shown to estimate base pair proton transfer rate coefficients that are in good agreement with recent experimental data. A range of electric fields in the order of 104 to 109 V m-1 is investigated based on their real-life medicinal applications which include gene therapy and cancer treatments. The MD trajectories confirm that electric fields up to 1.00 × 109 V m-1 have a negligible influence on the structure of the base pairs within DNA. The QM/MM results show that the application of large external electric fields (1.00 × 109 V m-1) parallel to the hydrogen bonds increases the thermodynamic population of the tautomers by up to one order of magnitude; moreover, the lifetimes of the tautomers remain insignificant when compared to the timescale of DNA replication.

Synthetic Biology Approaches To Enhance Microalgal Productivity

The major bottleneck in commercializing biofuels and other commodities produced by microalgae is the high cost associated with phototrophic cultivation. Improving microalgal productivities could be a solution to this problem. Synthetic biology methods have recently been used to engineer the downstream production pathways in several microalgal strains. However, engineering upstream photosynthetic and carbon fixation metabolism to enhance growth, productivity, and yield has barely been explored in microalgae. We describe strategies to improve the generation of reducing power from light, as well as to improve the assimilation of CO₂ by either the native Calvin cycle or synthetic alternatives. Overall, we are optimistic that recent technological advances will prompt long-awaited breakthroughs in microalgal research.

Nanosecond pulsed electric field processing of microalgae based biorefineries governs growth promotion or selective inactivation based on underlying microbial ecosystems

Nanosecond pulsed electric field treatment (nsPEF) is a technology-driven, resource-efficient approach fostering microalgae biorefineries for transforming them into economically viable scenarios. A processing window of 100 ns, 7 Hz, and 10 kV cm^-1 significantly leveraged phototrophic Chlorella vulgaris and bacterial counts up to + 50.1 ± 12.2% and + 77.0 ± 37.4%, respectively (n = 4; p < 0.05) in non-axenic cultures. Applying the same processing window decreased C. vulgaris (-17.1 ± 13.8%) and prokaryotic (-82.7 ± 14.6%) counts owing to alterations in the prokaryotic community diversity. Principle coordinate analysis of prokaryotic phenotypic fingerprints indicated that phenotype or metabolism related diversity changes in the prokaryotic community affected the treatment outcome. The study fosters the upsurge of industrial-scale nsPEF realization and the economic viability of microalgae biorefineries through improved process understanding and thus control. It perpetuates nsPEF applicability for microalgae feedstock production and several other applications within single-cell biorefineries in the bio-based domain.

Nanosecond pulsed electric fields modulate the expression of the astaxanthin biosynthesis genes psy, crtR-b and bkt 1 in Haematococcus pluvialis

Nanosecond pulsed electric fields (nsPEFs) have been extensively studied with respect to cellular responses. Whether nsPEFs can regulate gene expression and to modulate the synthesis of valuable compounds, has so far been only tested in the context of apoptosis in cancer cells. We used the unicellular algae Haematococcus pluvialis as system to test, whether nsPEFs could alter gene expression and to promote the biosynthesis of astaxanthin. We find that nsPEFs induce a mild, but significant increase of mortality up to about 20%, accompanied by a moderate increase of astaxanthin accumulation. Steady-state transcript levels of three key genes psy, crtR-b and bkt 1 were seen to increase with a maximum at 3 d after PEF treatment at 50 ns. Pulsing at 25 ns reduce the transcripts of psy, crtR-b from around day 2 after the pulse, while those of bkt 1 remain unchanged. By blocking the membrane-located NADPH oxidase RboH, diphenylene iodonium by itself increased both, the levels of astaxanthin and transcripts of all three biosynthetic genes, and this increase was added up to that produced by nsPEFs. Artificial calcium influx by an ionophore did not induce major changes in the accumulation of astaxanthin, nor in the transcript levels, but amplified the response of crtR-b to nsPEFs at 25 ns, while decreased in 50 ns treatment. When Ca²⁺ influx was inhibited by GdCl₃, the transcript of psy and bkt 1 were decreased for both 25 ns and 50 ns treatments, while crtR-b exhibited an obvious increase for the 25 ns treatment. We interpret these data in a working model, where nsPEFs permeabilise plasma and chloroplast membrane depending on pulse duration leading to a differential release of plastid retrograde signaling to the nucleus.

Two-step procedure for selective recovery of bio-molecules from microalga Nannochloropsis oculata assisted by high voltage electrical discharges

Two-step procedure with the initial aqueous extraction from raw microalgae Nannochloropsis oculata and secondary organic solvent extraction from vacuum dried (VD) microalgae were applied for selective recovery of bio-molecules. The effects of preliminary aqueous washing and high voltage electrical discharges (HVED, 40 kV/cm, 4 ms pulses) were tested. The positive effects of HVED treatment and washing on selectivity of aqueous extraction of ionics and other water-soluble compounds (carbohydrates, proteins and pigments) were observed. Moreover, the HVED treatment allowed improving the kinetic of vacuum drying, and significant effects of HVED treatment on organic solvent extraction of chlorophylls, carotenoids and lipids were determined. The proposed two-step procedure combining the preliminary washing, HVED treatment and aqueous/organic solvents extraction steps are useful for selective extraction of different bio-molecules from microalgae biomass.

Bio-refinery of Chlorella sorokiniana with pulsed electric field pre-treatment

The aim of this work was to investigate the potential of PEF technology for green extraction of microalgal pigments and lipids from fresh Chlorella sorokiniana suspensions. Efficiencies of PEF treatment and different solvent systems application to C.sorokiniana were compared to efficiencies of untreated biomass extraction. Differences in chlorophyll extraction of untreated and PEF treated C.sorokiniana were only seen at short extraction times. Beneficial PEF-effect was minimised for long-time extractions of larger algae quantities where yields aligned. Extraction attempts on C. sorokiniana lipids did not show increased extractability after PEF treatment, which underlined the statement of PEF representing a rather ineffective disruption method for microalgae holding rigid cell walls.

Continuous nanosecond pulsed electric field treatments foster the upstream performance of Chlorella vulgaris-based biorefinery concepts

Nanosecond pulsed electric field treatment (nsPEF) is an innovative, technology-driven, and resource-efficient approach to foster the upstream performance of microalgae-based biorefinery concepts to transform microalgae into economic more viable raw materials for the biobased industry. A processing window applying three treatments of 100 ns, 5 Hz, and 10 kV cm^-1 to industrially relevant phototrophic Chlorella vulgaris in the early exponential growth phase significantly increased biomass yields by up to 17.53 ± 10.46% (p = 3.18 × 10^-5). Treatments had limited effects on the carbon and pigment contents, but the protein content was decreased. The longest possible pulse width (100 ns) resulted in the highest biomass yield indicating underlying working mechanisms of enhanced cell proliferation based on intracellular and plasma membrane-related effects. The applicability to eukaryotes and prokaryotes, such as C. vulgaris and cyanobacteria highlights the possible impacts of nsPEF across multiple domains of the biobased industry relying on single-cell-based value-chains.

Pulsed electric field based cyclic protein extraction of microalgae towards closed-loop biorefinery concepts

Microalgae-based biorefinery concepts can contribute to providing sufficient resources for a growing world population. However, the performance needs to be improved, which requires innovative technologies and processes. Continuous extraction from Chlorella vulgaris cultures via pulsed electric field (PEF) processing might be a viable process to increase the performance of microalgae-based biorefinery concepts. In this study, increasing protein extraction rates were observed with increasing electric field strength, up to 96.6 ± 4.8% of the free protein in the microalgae. However, increased extraction rates negatively influenced microalgae growth after PEF treatment. A free protein extraction rate up to 29.1 ± 1.1% without a significant influence on microalgal growth after 168 h was achieved (p = 0.788). Within the scope of this work, a protocol for continuous protein extraction during microalgae cultivation by PEF processing was developed. The incorporation of innovative downstream into upstream processing could be a viable future concept.

Perspective on Pulsed Electric Field Treatment in the Bio-based Industry

The bio-based industry is urged to find solutions to meet the demands of a growing world population. In this context, increased resource efficiency is a major goal. Pulsed electric field (PEF) processing is a promising technological solution. Conventional PEF and the emerging area of nanosecond PEF (nsPEF) have been shown to induce various biological effects, with nsPEF inducing pronounced intracellular effects, which could provide solutions for currently faced challenges. Based on the flexibility and continuous operation of PEF and nsPEF processing, the technology can be integrated into many existing cultivation systems; its modularity provides an approach for inducing specific effects. Depending on the treatment conditions, selective inactivation, continuous extraction without impeding cell viability, as well as the stimulation of cell growth and/or cellular compound stimulation are potential applications in the bio-based industry. However, continuous treatment currently involves heterogeneous energy inputs. Increasing the homogeneity of PEF and nsPEF processing by considering the flow and electric field heterogeneity may allow for more targeted effects on biological cells, further increasing the potential of the technology for bio-based applications. We provide an overview of existing and potential applications of PEF and nsPEF and suggest that theoretical and practical analyses of flow and electric field heterogeneity may provide a basis for obtaining more targeted effects on biological cells and for further increasing the bio-based applications of the technology, which thereby could become a key technology for circular economy approaches in the future.

Effects of a pulsed electric field on nitrogen removal through the ANAMMOX process at room temperature

This study explored the effect of a pulsed electric field (PEF) on the anaerobic ammonium oxidation (ANAMMOX) process at room temperature (20 ± 1 °C). The influences of different modes of PEF (R1), a direct current electric field (R2) and a control reactor (R3) were determined through long-term tests. The results showed that R1 shortened the start-up time and led to excellent nitrogen removal. At this stage, the activities of key enzymes of R1 were much higher than those of R3. The high-throughput sequencing results showed that the relative abundance of functional bacteria in R1 was higher than that in R2 and R3. The mechanism by which the PEF enhanced ANAMMOX might be the improvement of the speed of ion and molecular migration that occurred by changing the permeability of the cell membrane under the PEF.