Isolation of a novel strain of Aeromonas media producing high levels of DOPA-melanin and assessment of the photoprotective role of the melanin in bioinsecticide applications

AIMS: To isolate a bacterium that produces high yield of melanin and to examine the effect of this bacterial pigment on the efficacy of a bioinsecticide. METHODS AND RESULTS: A novel melanin-producing bacterium, designated as strain WS, was isolated from the East Lake, Wuhan, China. Taxonomic studies of this strain indicate that it belongs to Aeromonas media. Physicochemical analysis of the pigment produced by strain WS (melanin WS) suggests that it is the authentic 3,4-dihydroxyphenylalanine (DOPA)-melanin. This melanin and that produced by Pseudomonas maltophilia P28 (melanin P28) share many biophysical properties, but the yield of the melanin WS is significantly higher than that of the melanin P28. In addition, the melanin WS appears to be more effective in the protection of a bioinsecticide against ultraviolet (UV) or solar radiation. At the concentration of 10 ppm, the melanin P28 exhibited no photoprotective effect on the bioinsecticide against UV radiation; in contrast, 5 ppm of melanin WS displayed an obvious protective effect. Similarly, the melanin WS displayed more protective effect on the bioinsecticide against solar radiation than the melanin P28 did over a 4-day period, with the effect being more dramatic for the last 2 days. CONCLUSIONS: We have isolated a novel bacterial strain of A. media that produces high levels of melanin. The melanin produced by this strain offers effective photoprotection of a commercial bioinsecticide BTI against UV and solar radiation. SIGNIFICANCE AND IMPACT OF THE STUDY: Our study suggests that the melanin produced by our newly isolated A. media strain has the potential to be used as a general photoprotective agent for bioinsecticides.