Bacterial metabolites and bio-factories: a movement towards natural photoprotection

This blogger is all for naturally derived ingredients in cosmetic compositions‒ providing they are

ecologically friendly, of course. 

So when I read about a recent investigation into two bacterial pigments that have shown to improve sun protection factor (SPF), my interests were ignited. The original story can be found on cosmeticsdesign-europe.com.

SPF and UV

UVA (315-400nm wavelength) and UVB (280-315nm wavelength) are the prime forms of UV-radiation emitted by the sun that are capable of being absorbed by human skin. UVA and UVB penetrate the dermis and epidermis, respectively, UVB inducing skin burning and UVA causing premature skin ageing, hyperpigmentation, inflammation and melanomas. The latter has been shown to be triggered by UV-induced mutagenic DNA damage in the form of cyclobutane-pyrimidine dimers (CPDs) and 6-4 photoproducts (6-4PPs) (1). Special UV filters in commercial sun cream formulations protect human skin from UVA and UVB damage. The efficacy of a sun screening ingredient is known as the sun protection factor (SPF), described as:

Minimal erythema dose (MED)= lowest UV irradiation dosage capable of elicitting a minimal and noticeable erythema (skin redness) on unprotected skin. To be effective, a sunscreen ingredient should have a widespread absorbance between 290-400 nm (2).

Current commercial sun creams

Sun creams are laden with ingredients that reflect, absorb and scatter UV-radiation. Inorganic substances e.g. zinc oxide and titanium oxide reflect high-energy photons away from the skin, whilst organic substances including oxybenzene and p-amino benzoic acid absorb UV-radiation and emit lower energy rays. Yet these compounds are under scrutiny for adverse health effects in human skin. Zinc oxide nanoparticles have been found to be genotoxic, causing oxidative stress and lipid peroxidation, and organic sunscreens may be triggered by UV to generate photosensitizer compounds which may react with cutaneous molecules, inducing adverse effects on skin (3). Yet humans are not only affected; organic sunscreen benzophenone-2 (BP-2) has been shown to be a photo-toxicant to the coral Stylophora pistillata, transforming coral planulae into a deformed state and inducing DNA lesions, with adverse effects such as necrosis in the dermis and gastrodermis intensified in light and autophagy and autophagic cell death amplified in darkness, upon exposure to BP-2 (4). With a rising demand for substitution of chemical sunscreens with bio-sunscreens comes a search for natural, environmentally sustainable and non-toxic sources of UV-screening compounds.

Current research: bacteria

Cyanobacterial bio-factories:  

The photosynthetic Cyanobacteria inhabiting a diverse array of ecological niches from the thermophilic to halophilic, are exposed to oodles of UV-radiation. To neutralise the damaging effects of UV exposure, cyanobacteria have cultivated mechanisms for generating metabolites, e.g. mycosporine-like amino acids (MAA) and scytonemin, absorbing wavelengths in the UVA and/or UVB spectrum. Unlike wild sources (e.g. marine macroalgae) of these same UV-screening metabolites in bio-suncreens, whose biomass and metabolites may fluctuate seasonally, cyanobacterial growth is not dependent on season so can be cultivated, for instance, in photobioreactors, to obtain their natural products. More than 50 cyanobacterial genome sequences exist, enabling genome comparison amongst cyanobacterial strains and their relatives for genetic optimisation. Therefore, cyanobacteria can be further genetically optimised to create commercially relevant UV-sunscreen ingredients at an industrial level, by establishing cheaper and sustainable cultivation strategies (5). 

Bacterial pigments: Two bacterial pigments, prodigiosin and violacein, from UV-tolerant Serratia marcescens and Chromobacterium violaceum, respectively, have recently been shown to improve SPF, whilst demonstrating antioxidant and antimicrobial properties. Prodigiosin and violacein are constitutively produced without UV exposure, indicating their antimicrobial activity against Gram positive bacteria such as Staphylococcus aureus as well as marine microalgae. The study determined SPF by spectrophotometry as shown in the graph below, SPF values for the commercial sunscreens of SPF 15, 24 and 40 increased 19%, 22% and 10% with addition of violacein, respectively, and 65%, 42% and 20% with addition of prodigiosin, respectively. These results suggest that the pigments cause conformational changes in the active ingredients of the commercial sunscreens, boosting their photoprotective qualities (6).

 

 In conclusion: biotechnological value

The current research presents potential for novel bacterial bio-sunscreening compounds. Further investigation is required at the molecular level for the proficient biosynthesis of UV sunscreen substances, and subsequent genetic manipulations for optimisation of compounds and enhanced synthesis. Despite additional studies being a necessity to test cytotoxicity, genotoxicity and photostability in mammalian cells for human use, this blogger would like to see whether genes for such metabolites are able to be isolated and transduced into other expression systems optimised for product expression, such as Escherichia coli strains, to produce vast quantities for commercial use. 

For more information:

(1) UV-induced DNA damage and repair: a review.

(2) Determination of sun protection factor (SPF) of sunscreens by ultraviolet spectrophotometry

(3) Zinc oxide nanoparticle induced genotoxicity in primary human epidermal keratinocytes

(4) Toxicological effects of the sunscreen UV filter, benzophenone-2, on planulae and in vitro cells of the coral, Stylophora pistillata; 

     Sunscreen chemical threatens coral reefs

(5) Cyanobacteria as bio-factories for production of UV-screening compounds

(6) Towards an understanding of bacterial metabolites prodigiosin and violacein and their potential for use in commercial sunscreens