ID: 2243

• Title:
  Investigation of the combined effect of plasma and pulsed electric field treatment on Chlorella vulgaris microalgae
  
  Authors:
  

  Jonynaite, Kamile - 1
  Uscila, Rolandas - 2
  Kersulis, Skirmantas - 1
  Kavaliauskas, Zydrunas - 2 
  Marcinauskas, Liutauras - 2 
  Stirke, Arunas - 1
  Stankevic, Voitech - 1
  1 - State Research Institute, Center for Physical Sciences and Technology, Sauletekio ave. 3, Vilnius, Lithuania
  2 - Lithuanian Energy Institute, Plasma Processing Laboratory, Breslaujos str. 3, Kaunas, Lithuania

  
  
  Abstract:
  Pulsed electric field (PEF) exposure has been one of the most studied algae treatment technologies over the last decade. Depending on the type of algae, different PEF treatment parameters are used to extract valuable algal compounds such as lipids, proteins, etc. [1,2]. Unfortunately, the efficiency of PEF extraction is still not high enough to compete with conventional technologies [3].
  
  Recent studies in mammalian and bacterial cells have shown that the efficacy of PEF can be enhanced by combining it with a non-thermal plasma [4,5]. There is evidence that plasma-induced radicals lead to lipid oxidation in cell membranes, resulting in a decreased membrane integrity and increasing the efficacy of the combined treatment compared to plasma or PEF alone. In addition, combined plasma and PEF treatment has been shown to act synergistically to increase intracellular ROS generation, inducing additional cytotoxicity and changes in molecular signalling pathways [4]. However, no similar studies have been performed with microalgae. Therefore, the aim of the present study was to investigate the combined effects of plasma and PEF on the freshwater microalga Chlorella vulgaris.
  
  For this purpose, gliding arc discharge and PEF technologies were applied to Chlorella vulgaris. First, algae biomass was treated with plasma under the following parameters: compressed air flow ~22.8 l/min, distance between knife-edge electrodes and algae suspension surface 30 mm, treatment duration 300 s, generator voltage 50-250 V and frequency 270 kHz. Immediately afterwards, the plasma-treated algae suspension was processed with the following PEF parameters: pulse duration 7 μs, 1-10 exponential pulses at a frequency of 1 Hz, with the resulting electric field strength varying from 24-25 kV/cm. Subsequently, changes in medium composition, cell permeability, viability, extracted protein content of untreated and treated algal suspensions were determined.
  
  The results showed that the effect of the combination treatment depends on the plasma voltage parameters. The application of 130 V plasma and 1 PEF pulse resulted in a slight increase in algal cell permeability compared to PEF alone. At 24 h post-treatment, SYTOX green fluorescence showed nucleic acid release in the supernatant, which was at the same level as the positive ultrasound-treated control, indicating cell death. However, neither the algal inactivation rate nor the protein yield was increased due to the increased efficiency of cell permeabilization. The opposite trend was observed for plasma and PEF treatments above 170 V. Although algal cells showed a high level of cell permeabilization after the combined treatment, nucleic acid diffusion tended to decrease with increasing plasma voltage. This was most pronounced after exposure to 210-250 V plasma and PEF, where the DNA released was similar to that of completely untreated algae, even 24 h after exposure. In addition, exposure to high voltage plasma and PEF resulted in a reduced concentration of extracted proteins.
  
  In conclusion, the results suggest that direct plasma treatment induces unknown cellular changes affecting PEF efficiency and altering the mechanism of C. vulgaris death.
  
  Keywords:
  Chlorella vulgaris; microalgae; plasma, pulsed electric field (PEF)
  
  Refs:
  [1] M. Coustets, V. Joubert-Durigneux, J. Hérault, B. Schoefs, V. Blanckaert, J.-P. Garnier, J. Teissié. Bioelectrochemistry. 103 (2015) 74–81. https://doi.org/10.1016/j.bioelechem.2014.08.022. [2] R. Straessner, M. Nikolausz, A. Silve, N. Nazarova, R. Wuestner, I. Papachristou, S. Akaberi, K. Leber, G. Mueller, W. Frey. Algal Research. (2022) 102950. https://doi.org/10.1016/j.algal.2022.102950. [3] M.-C. Sommer, M. Balazinski, R. Rataj, S. Wenske, J.F. Kolb, K. Zocher. Microorganisms. 9 (2021) 1452. https://doi.org/10.3390/microorganisms9071452. [4] C.M. Wolff, J.F. Kolb, K.-D. Weltmann, T. von Woedtke, S. Bekeschus. Cancers (Basel). 12 (2020) 845. https://doi.org/10.3390/cancers12040845. [5] R. Mentheour, Z. Machala. Frontiers in Physics. 10 (2022). https://www.frontiersin.org/articles/10.3389/fphy.2022.895813 (accessed October 27, 2022).
  
  Topic 1:
  1. Biological responses (molecular, subcellular, cellular and intercellular)
  
  Topic 2:
  5. Exposure devices and methods