Protection against solar UV radiation in organisms includes the production of secondary metabolites such as pigments that can absorb UV and visible light. In this study, the vioA gene encoding tryptophan 2-monooxygenase involved in the biosynthetic pathway of the violacein-like pigment purple violet (PVP) was cloned and sequenced from an Antarctic bacterium Janthinobacterium sp. Ant5-2. A non-pigmented vioA mutant strain was obtained following mini-Tn10 transposon mutagenesis that produced less extrapolymeric substances (EPS) and showed impaired survival to freeze-thaw cycles at 4°C. The survival of the vioA mutant strain during the exponential and stationary growth phase was significantly reduced when exposed to UVB (320 nm) and UVC (254 nm) light (dose range: 0-300 J/m²). Reduced viability of the mutant strain was noted at 4°C following nutrient deprivation and exposure to UV light. Pigment production was increased in surviving cells following increased doses of both UVB and UVC. Interestingly, at higher doses, i.e. 100 and 300 J/m², the pigmented wild strain showed better survival to harmful UVC compared to UVB. This could be attributed to the structure of the pigment, which has absorption maxima in the visible range (575 nm) as well as in the UVC range (270 nm). In conclusion, this study defines the photoprotective role of PVP in Janthinobacterium sp. Ant5-2 against UV radiation using single gene mutation. Perhaps the photoprotective role of PVP in this bacterium is one of the key adaptive characteristics that define their survival in the extreme conditions of the Antarctic, especially during the austral summer months. INTRODUCTION High-energy photons in solar UV radiation are considered the most harmful component to the biological system. macromolec...... half of paper ......x, which is involved in biofilm formation mediated by quorum sensing (Morohoshi et al., 2010). Therefore, it is likely that loss of vioA affected biofilm formation in Ant5-2. Furthermore, colony morphology demonstrated that PVP had a substantial effect on the structural organization of colony biofilms (Fig. 4). The mechanisms by which pigment production controls colony morphology and EPS production are likely a complex question yet to be determined (Dietrich et al., 2008). Until recently, the potential role of pigments as secondary metabolites that modulated the cellular physiology of microorganisms under extreme environmental conditions was overlooked (Hernandez & Newman, 2001). This study provides evidence for the role of PVP as a secondary metabolite in UV resistance and suggests its primary functions in Ant5-2 residing in extreme Antarctic conditions.