Production of mycosporine-like amino acids from Euhalothece sp. for use as a photoprotectant

Abstract

Protecting skin from harmful UV radiation is a well-recognized health imperative. Given that UV exposure is a primary cause of sunburn, premature skin aging, and significantly increases the risk of skin cancers including melanoma, the use of sunscreens has become a vital tool in public health strategies, leading to their widespread use. Whilst effective, there are concerns about the longterm effects of synthetic sunscreen ingredients that are driving the search for natural alternatives. Cyanobacteria are constantly exposed to short-wave ultraviolet (UV) radiation as they require solar energy to perform processes such as photosynthesis and nitrogen fixation. These microorganisms have developed multiple UV defence mechanisms to protect themselves from the higher amounts of UV radiation in the environment. Some of these strategies include mat formation, active repair mechanisms, accumulation of detoxifying enzymes and antioxidants, and synthesis of photo-protectants such as mycosporine-like amino acids (MAAs) (Rastogi et al., 2014). Mycosporine-like amino acids have gained a lot of interest in cosmetics and pharmaceutical industries since they act as natural photoprotectants and have shown to aid in overcoming rashes, pigmentation, aging as well as possess anticancer properties. Mycosporine-like amino acids are secondary metabolites produced by cyanobacteria in response to environmental stress such as salinity, temperature, high light irradiance and UV wavelengths. Cyanobacteria are a good source of MAAs, can be easily cultivated and requires a very short generation time, making them an environmentally friendly source of alternate photoprotectants. This study focuses on elucidating factors affecting MAA production using indigenous halophilic cyanobacteria Euhalothece sp. Light, salinity, and nitrogen concentration were optimised using response surface methodology to maximise MAA production. UV light irradiance was used to further induce expression of the protein. DNA was extracted and purified for gene expression analysis targeting the mys gene cluster. Purified MAAs were tested for their antioxidant activity and their stability under a range of temperatures, pH and UV irradiance to assess their potential for commercial use. Preliminary experiments confirmed the individual influence of abiotic factors, with light and salinity significantly impacting MAA production (p = 0,0395 and p = 0,0009 respectively). Using response surface methodology (RSM), the effects of light irradiance, salinity, nitrogen concentration, and UV exposure were optimized. A significant model (p = 0,0099) was developed, predicting optimal MAA production under 92 hours of UV exposure, nitrogen deficiency, and high salinity (90 or 120 g/L). Using 90 g/L salt was more cost-effective, requiring 28% less salt for a 5,36% reduction in MAA production. Molecular analysis through PCR confirmed the presence of the MAA biosynthetic gene cluster utilizing the OMT and DHQS and demonstrated its upregulation in response to UV exposure through qPCR. The UV-exposed culture showed amplification around cycle 14 while the control showed amplification around cycle 26. Purified MAAs demonstrated antioxidant activity and high stability across varying conditions over 48 hours. This included room temperature and neutral pH (p = 0,02), 4°C (p = 0,046), 40°C (p = 0,041) and UV irradiance (p = 0,04). These compounds showed excellent stability across various conditions, effectively maintaining their protective abilities. While their antioxidant capacity was measured (50,15%), it was clear that the main strength of MAAs lies in their strong UV protecting ability, making them highly suitable as active ingredients. This study demonstrates the potential of MAAs from Euhalothece sp. as a highly stable, effective, naturally derived, and industrially viable product. The optimized culture conditions, validated by molecular techniques, coupled with the high stability and additional beneficial properties of MAAs, position them as a compelling natural resource. Mycosporine-like amino acids can significantly advance photoprotection strategies and offer several other valuable applications in the cosmetic and pharmaceutical industries.