
Violacein is a secondary metabolite produced by microbes. It is a blue-violet pigment and insoluble in water. Violacein is an indole derivative formed by the condensation of two modified L-tryptophan molecules. Since violacein was found in late 19th century, studies have been done to explore its biofunction. Recently, intensive research has found that violacein displays important biological activities as a potential anti-tumor, antiviral drug and bio-dye. Violacein has received much attention due to its broad application prospects in textiles and dyeing, plant pathogenic fungi control and medicine field such as viral and tumor therapy.
Studies have indicated that violacein has the following bioactivities: (1) Broad-spectrum antibacterial activity such as staploylococcous aureus, Bacillus sp, streptococcus sp, mycobacterium, Neisserig, pseudomonas (Sanchez et al., Reevaluation of the Violacein Biosynthetic Pathway and its Relationship to Indolocarbazole Biosynthesis. Journal 2006. 7, 1231-1240); (2) antioxidant activities (Konzen et al., Antioxidant properties of violacein: possible relation on its biological function. Journal 2006. 14, 8307-8313); (3) anti-tumor activities (de Carvalho et al., Cytotoxic activity of violacein in human colon cancer cells. Journal 2006.); (4) anti-viral activities; (5) anti-protozoan; and (6) process various texture as natural bio-dye (Akira SHIRATA, Isolation of Bacteria Producing Bluish-Purple Pigment and Use for Dyeing. Japan Agricultural Research Quarterly. 2000. 34). In a word, violacein possesses significant medical values and broad prospect of industrial application.
Among the violacein-producing strains, most research has been focused on the strain Chromobacterium violaceum. The complete genome sequence of C. violaceum was completed in 2003, and this provided the basis for the violacein biosynthesis pathway analysis and application. However, the violacein biosynthetic gene cluster was originally reported to be consisted of four related genes. Recently, the whole violacein biosynthesis pathway was almost clear till the fifth gene (vioE) was found. The violacein biosyntheis involves one cluster consisting of five genes including vioA, vioB, vioC, vioD, and vioE respectively and span 7.3 kb.
Deoxyviolacein is a structural analog of violacein with one less oxygen atom and generally appears as a by-product in violacein biosynthesis. Due to the very low proportion of deoxyviolacein in the blue-purple pigment with the amount of only one tenth of violacein production, it is difficult to get enough deoxyviolacein for the analysis of its properties and function. To date, few research works have been done internationally on methods and technologies of the deoxyviolacein isolation. Moreover, little research work has been done on the properties and bioactivities of deoxyviolacein due to its low production and the difficulties on the isolation and purification. Currently, no specific function could be assigned to deoxyviolacein except its inhibitory activity on protozoa (Matz, C et al. Marine Biofilm Bacteria Evade Eukaryotic Predation by Targeted Chemical Defense. PLoS ONE, (2008) 3(7): e2744). Our previous research indicated that deoxyviolacein had better dyeing effect and anti-bacterial activity than violacein. Thus, it is possible to speculate that deoxyviolacein can have potential applications as violacein, and strengthening the basic and applied research on deoxyviolacein has important scientific and application value. Currently, it is urgent to invent effective ways for efficient production of deoxyviolacein.