Reconstruction of the violacein biosynthetic pathway from Duganella sp. B2 in different heterologous hosts

Abstract

Violacein is a bacteria-originated indolocarbazole pigment with potential applications due to its various bioactivities such as anti-tumor, antiviral, and antifungal activities. However, stable mass production of this pigment is difficult due to its low productivities and the instability of wild-type violacein-producing strains. In order to establish a stable and efficient production system for violacein, the violacein synthesis pathway from a new species of Duganella sp. B2 was reconstructed in different bacterial strains including Escherichia coli, Citrobacter freundii, and Enterobacter aerogenes by using different vectors. The gene cluster that encodes five enzymes involved in the violacein biosynthetic pathway was first isolated from Duganella sp. B2, and three recombinant expression vectors were constructed using the T7 promoter or the alkane-responsive promoter PalkB. Our results showed that violacein could be stably synthesized in E. coli, C. freundii, and E. aerogenes. Interestingly, we found that there were great differences between the different recombinant strains, not only in the protein expression profiles pertaining to violacein biosynthesis but also in the productivity and composition of crude violacein. Among the host strains tested, the crude violacein production by the recombinant C. freundii strain reached 1.68 g L(-1) in shake flask cultures, which was 4-fold higher than the highest production previously reported in flask culture by other groups. To the best of our knowledge, this is the first report on the efficient production of violacein by genetically engineered strains.

Influence of Environmental Factors on the Production of Violacein Synthesized By Janthinobacterium lividum

“…3b). Several authors have reported that the violacein crude extract usually is found as a mixture of violacein and deoxyviolacein [21,29,32,38]. Particularly, Rodrigues et al [42] reported that, by separating the mixture of these compounds, it can be obtain two completely separate fractions: the first peak containing violacein and subsequently deoxyviolacein [42,43].…”

“…It is known as well, that for some microorganisms, carbon sources with rapid metabolisms result in an increase in cellular mass and a decrease of secondary metabolic production, however the use of carbon sources of slower consumption results in a decrease of cellular growth and an increase in secondary metabolic production [29] which let us understand the ability of J. lividum to synthesize pigment using glycerol as carbon source. Similarly, it is reported that carbon sources of easy consumption, such as glucose or fructose, may affect violacein biosynthesis process, since they stimulate biomass growth and thus reduce secondary metabolic production [21,29]. Ahmad et al [26] suggests the existence of genetic repression mechanisms during the production of violacein by C. violaceum under high concentration of glucose, which can be associated with the observed in this research with tryptone medium, where could be some interaction between the carbon compounds, leading into repression systems.…”

“…Due to its biotechnological potential, numerous studies have been done indicating that Chromobacterium violaceum and Janthinobacterium lividum are primarily responsible for its synthesis [3][4][5]9,21,22]. Violacein has an indole derivative structure [8,15,17,18,21] characterized as C20-H13-N3-O3 [4,22,23]. The pigment is insoluble in water but soluble in alcohols (methanol, ethanol) and acetone.…”

“…Violacein is a purple pigment product of the secondary metabolism of bacteria, whose biological activities have been widely reported, including antimicrobial activity (antibacterial, antiviral, antiprotozoal and antifungal) [3,4,[6][7][8][9][10][11][12][13][14] anticancer activity [15][16][17][18][19] antioxidant activity [20] and recent studies also show insecticidal activity [5]. Due to its biotechnological potential, numerous studies have been done indicating that Chromobacterium violaceum and Janthinobacterium lividum are primarily responsible for its synthesis [3][4][5]9,21,22]. Violacein has an indole derivative structure [8,15,17,18,21] characterized as C20-H13-N3-O3 [4,22,23].…”

Characterization and Identification of Productivity-Associated Rhizobacteria in Wheat

“…The best-fit model is indicated in the lower right-hand corner for each panel. Janthinobacterium are producers of the antibiotic violacein, a known inhibitor of viruses, fungi, and nanoflagellates (19). Their numerical abundance may reflect the production and activity of these antipredatory or antiparasitic compounds, since predation and parasitism are major known factors shaping the rhizobacterial community (26).…”