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

Synopsis<br/>Objectives<p style="background: none; margin: 0px 0px 1em; padding: 0px; outline: 0px; border: 0px currentColor; border-image: none; line-height: 1.5em; font-size: 12px; vertical-align: baseline;">To exploit the microbial ecology of bacterial metabolite production and, specifically, to: (i) evaluate the potential use of the pigments prodigiosin and violacein as additives to commercial sunscreens for protection of human skin, and (ii) determine antioxidant and antimicrobial activities (against pathogenic bacteria) for these two pigments.<br/><br/>Methods<br/>Prodigiosin and violacein were used to supplement extracts of <i>Aloe vera leaf and <em style="font-style: italic; margin: 0px; padding: 0px; outline: 0px; border: 0px currentcolor; border-image-source: none; border-image-slice: initial; border-image-width: initial; border-image-outset: initial; border-image-repeat: initial; vertical-align: baseline; background-image: none; background-attachment: initial; background-color: initial; background-size: initial; background-origin: initial; background-clip: initial; background-position: initial; background-repeat: initial;">Cucumis sativus </em>(</i>cucumber) fruit which are known to have photoprotective activity, as well as some commercial sunscreen preparations. For each, sunscreen protection factors (SPFs) were determined spectrophotometrically. Assays for antimicrobial activity were carried out using 96-well plates to quantify growth inhibition of <i>Staphylococcus aureus and Escherichia coli</i>. <br/>Results<br/>For the plant extracts, SPFs were increased by an order of magnitude (i.e. up to ~3.5) and those for the commercial sunscreens increased by 10–22% (for 4% w/w violacein) and 20–65% (for 4% w/w prodigiosin). The antioxidant activities of prodigiosin and violacein were approximately 30% and 20% those of ascorbic acid (a well-characterized, potent antioxidant). Violacein inhibited <em style="line-height: 1.5em; margin: 0px; padding: 0px; outline: 0px; border: 0px currentcolor; border-image-source: none; vertical-align: baseline; background: none;">S. aureus (IC<sub style="background: none; margin: 0px; padding: 0px; outline: 0px; border: 0px currentColor; border-image: none; line-height: 0.7em; font-size: 0.8em; white-space: nowrap;">506.99 ± 0.146 μM) but not <em style="background: none; margin: 0px; padding: 0px; outline: 0px; border: 0px currentColor; border-image: none; vertical-align: baseline;">E. coli, whereas prodigiosin was effective against both of these bacteria (IC<sub style="margin: 0px; padding: 0px; outline: 0px; border: 0px currentcolor; border-image-source: none; line-height: 0.7em; font-size: 0.8em; background: none;">50 values were 0.68 ± 0.06 μM and 0.53 ± 0.03 μM, respectively).<br/></sub></em></sub></em><br/>Conclusion<br/>The bacterial pigments prodigiosin and violacein exhibited antioxidant and antimicrobial activities and were able to increase the SPF of commercial sunscreens as well as the extracts of the two plant species tested. These pigments have potential as ingredients for a new product range of and, indeed, represent a new paradigm for sunscreens that utilize substances of biological origin. We discussed the biotechnological potential of these bacterial metabolites for use in commercial sunscreens, and the need for studies of mammalian cells to determine safety.</p>