First Report on Photodynamic Inactivation of Archaea Including a Novel Method for High-Throughput Reduction Measurement.

Daniel B Eckl,Harald Huber,Wolfgang Bäumler

doi:10.1111/php.13229

Daniel B Eckl, Harald Huber + Show 1 more

Open Access

https://doi.org/10.1111/php.13229

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Abstract

Archaea are considered third, independent domain of living organisms besides eukaryotic and bacterial cells. To date, no report is available of photodynamic inactivation (PDI) of any archaeal cells. Two commercially available photosensitizers (SAPYR and TMPyP) were used to investigate photodynamic inactivation of Halobacterium salinarum. In addition, a novel high-throughput method was tested to evaluate microbial reduction in vitro. Due to the high salt content of the culture medium, the physical and chemical properties of photosensitizers were analyzed via spectroscopy and fluorescence-based DPBF assays. Attachment or uptake of photosensitizers to or in archaeal cells was investigated. The photodynamic inactivation of Halobacterium salinarum was evaluated via growth curve method allowing a high throughput of samples. The presented results indicate that the photodynamic mechanisms are working even in high salt environments. Either photosensitizer inactivated the archaeal cells with a reduction of 99.9% at least. The growth curves provided a fast and precise measurement of cell viability. The results show for the first time that PDI can kill not only bacterial cells but also robust archaea. The novel method for generating high-throughput growth curves provides benefits for future research regarding antimicrobial substances in general.

Highlights

At the very beginning of the 20th century, Oskar Raab and Hermann von Tappeiner discovered that Paramecium cells can be inactivated by simultaneous application of light and acridine dyes by a process called photodynamic mechanism [1,2,3]
The data of the reference spectra with the photosensitizer dissolved in ultrapure water are not shown, as the curves did not differ from the nonirradiated sodium chloride controls
Attachment assays showed that TMPyP binds much more efficient to the tested archaeal cells than SAPYR does. 73 % of TMPyP (3.62 μmol L−1) attached to cells at a concentration of 5 μmol L−1

Summary

Introduction

At the very beginning of the 20th century, Oskar Raab and Hermann von Tappeiner discovered that Paramecium cells can be inactivated by simultaneous application of light and acridine dyes by a process called photodynamic mechanism [1,2,3]. It is well known that light is absorbed by such a photosensitizer molecule, which thereby generates reactive oxygen species (ROS). These ROS can destroy cells via oxidation of various cellular structures. The photodynamic mechanism found its way into different medical fields termed photodynamic therapy of tumors (PDT) [4]. Another promising application of the photodynamic mechanism is PDI of microorganisms that has been proven efficient against viruses, bacteria and fungi. A variety of molecules were successfully tested as photosensitizers to be used in PDI like porphyrins, phthalocyanines, phenalenones, phenothiazines or flavins [5]

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