Cyanobacterial Sunscreen: A Shield Against UV and Environmental Impact

Due to the damaging effects of ultraviolet rays (UV), strategies are applied to intercept these high-energy wavelengths. As stated by Schroeder P. , Krutmann J. (2010), infrared energy also plays a role in inflicting deterimental effects on human skin; therefore, cyanobacterial sunscreen (CBS) should posess UV-intercepting and infrared-intercepting properties for it to become an effective barrier against solar radiation.

As stated by Thompson, S. C., et al (2018), regular use of sunscreen can reduce solar keratoses due to their ability to filter UV rays.

Their study found that their sunscreen group in their study experienced lesser lesions, thus implies the reduction of skin cancer risks.

One such effects of sun exposure is the accumulation of rough and damaged skin patches (solar keratoses). Chlorofluorocarbons that are broken down to free radicals by UV wavelengths interact with the ozone layer, thus many organizations encourage the use of sunscreen. (Sandra C. et al, 1993). According to the same source, solar keratoses is the progenitor of skin cancer. Dermatologists recommend the use of sunscreen with sun protection factor (SPF) of 30 which filters 97% of UV wavelengths.

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Thus, the researchers aim to create a sunscreen that at least has SPF 15 (93%) and SPF 30 at most; however, scytonemin was found to absorb only 90% of UV rays.

According to a study by Corinaldesi, C. et al (2018), mineral sun screen composed of inorganic compounds such as zinc oxide and titanium dioxide interrupts the symbiotic relationship of Acropora spp. and zoozanthalae. Moreover, the reseachers found Eusolex® T2000 and Optisol™ to have minor effect on corals. Due to compounds that interfere with marine-life, it is necessary to incorporate compounds with the least or no effect to corals so as to minimize coral bleaching and lower coral mortality.

In a similar study, the researchers found that wash-off water with traces of ethylhexylmethoxy-cinnamate (EHMC) and octocrylene (OC) from sunscreens can cause bleaching and death (He, T. et al, 2019). S. caliendrum and P. damicornis both demonstrated high mortality.

Aside from the aforementioned compounds, a study conducted by Downs, C. A. et al (2016), a UV filter called oxybenzone is a photo-toxicant organic compound found in most commercial sunscreens. Despite its adverse effects after being aggravated by light, larval forms of Stylophora pistillata demonstrated a shift from a motile to a sessile state in oxybenzone concentrations regardless of light levels. Moreover, oxybenzone's genotoxicant properties also induce a positive relationship between its concentration levels to DNA-AP lesions.

Though oxybenzone disrupts both the developmental and embryonic growth of corals, the study by Coronado, M. et al (2008) emphasized a disruption in hormonal, specifically estrogenic, activity of two different fish species. Concentrations of oxybenzone lower the eggs laid by Oryzias latipes significantly after seven days. The amount of eggs laid normalized after 21 days. While in this experiment, the concentration of oxybenzone is higher than found in the environment, these data demonstrate the endocrine-disrupting ability of this organic molecule.

Due to the effects of this compounds, it is crucial to switch to a potential and promising alternative. In a study conducted by Balskus, E., Case, R., Walsh, C. (2011), cyanobacteria contain a small molecule called scytonemin which is used for protection from UV-A and UV-B exposure. This results in the formation of a stable, protective layer that absorbs 90% of further radiation (Garcia-Pichel & Castenholz, 1991 as cited by Balskus, E., et al). Therefore, scytonemin could possibly have an SPF lower than 15.

Scytonemin can perform UV screening activity without any metabolic investment added to it (Singh, et al). It is highly stable under different abiotic stressors. Likewise, it also has antioxidant activity, and prevent damages to the cell resulting from reactive oxygen species produced upon UV-radiation exposure (Matsui et al., 2012; Rastogi et al., 2015). With the potential of scytonemin to block UV radiation, it suggests opportunities for utilization by the industry of cosmetics

According to Pathak, J. et al (2015), scytonemin and mycosporine-like amino acids (MAAs) are partially isolated and verified through high-performance liquid chromatography (HPLC) analysis. Areas with high levels of solar radiation such as roof tops and agricultural fields exhibited an abundance in scytonemin, particulary found in Scytonema sp., Lyngbya sp. and Nostoc sp. Therefore, it will be imperative to sample cyanobacteria from areas conducive to their living, and to sample large amounts of scytonemin in areas prone to sunlight and desiccation.