By using non-destructive single-cell optical technologies, researchers were able to explore and reveal distinct responses of individual spores to microwave radiation.
Microwaves are defined as nonionizing electromagnetic radiations with a frequency range of 300 MHz to 300 GHz. The energy from microwaves can generate heat, penetrate microorganisms and cells, and has the potential to directly break chemical bonds in molecules like DNA. Since the high absorption and penetrability of microwaves has the ability to affect biological activities, environments exposed to microwave radiation have great impacts on organisms. Therefore, the effects of microwave radiation and its downstream consequences or impacts on organisms have long been of great interest in biological and biomedical research.
In extremely harsh environments, bacteria can enter a spore state, which consists of special multi-layer protective structures that can lock DNA stably. This allows bacteria to persist in harsh conditions like high temperatures and toxic chemicals. Previous studies have focused on understanding the mechanism for spore killing and have discovered that microwave radiation at temperatures of approximately 100°C is effective in killing spores. However, exactly how microwave radiation affects spores remains unknown.
Therefore, in this study published in Journal of Innovative Optical Health Sciences, researchers were determined to examine the impacts of microwave radiation on individual spore at single-cell level — namely its effects on spore survival, molecules, germination and growth, and structure.
After being exposed to microwave radiation at power levels of 50 W, 100 W, and 150 W, the survival rates of the spores were determined. Microwave-treated spores were found to have lower survival rates compared to untreated spores. Despite the short duration of the microwave treatments, which only lasted for one minute, the difference in spore survival between microwave-treated and untreated spores was significant.
To determine the changes in spore molecules after microwave treatments, the average Raman spectra from 30 single spores were obtained by laser tweezers Raman spectroscopy. Results revealed that that microwave exposure caused damage to DNA and nucleic acid denaturation, which increased in severity as microwave power level increased.
Live-cell microscopy was used to lock-in live-cell images in focus to analyse spore germination and growth. Bright-field images of microwave-treated and untreated spores were captured every minute over a four-hour period. Results showed that increasing the microwave power level led to decreased spore germination and growth, indicating that microwave radiation affects both germination and growth. The researchers also observed a reduction in cell lengths and the rates of cell lengths, further indicating that microwave treatment affects spore growth.
In order to examine the impact of microwave radiation on spore structure, atomic force microscopy was used to capture images of microwave-treated and untreated spores. It was discovered that the spores treated with microwave radiation at 150 W displayed protuberances covering the entire surface and had a rough appearance, indicating that microwave radiation affects spore structure. Furthermore, increasing microwave power caused a reduction in length, width, and height (i.e., volume) and an increase in average roughness of the spores.
The team’s work provides support for past research on the effectiveness of microwave radiation in reducing the survival rate of spores. But beyond that, their results also demonstrate the team’s novel non-destructive optical technologies that are suitable for analysing the impacts of microwave radiation on living single cells. These findings unlock a new lens for analysing living single cells for various applications, such as in the fields of molecular and biomedical research. [APBN]
Source: Qiu et al. “Single-cell analysis reveals microbial spore responses to microwave radiation,” J. Innov. Opt. Health Sci. 16(2), 2244004 (2023).