Ramlibacter tataouinensis, a new genus and species isolated a semi-arid region of South Tunisia, presents two different morphologies: cysts resistant to desiccation and highly motile rod-shaped cells. An unusual characteristic of its cell cycle is that it could make ‘rod-rod’ division but also ‘cysts-cysts’ division if water is available. Due to the strong correlation between light, heat and desiccation in desert environment, the effect of light on this cell cycle was studied. Blue light of low intensity strongly inhibits the cell division of Ramlibacter tataouinensis. Red light induces the ‘rod-rod’ division, while almost uniquely ‘cysts-cysts’ division occurs in the dark. Analysis of the genome reveals the presence of four blue light sensors and two red light sensors. The biochemical and biophysical properties of these two bacteriophytochromes are characterized. One of these bacteriophytochromes, RtaBphP2, absorbs maximally at 755 nm in the dark, typical to a Pfr form. The light-induced Pr form presents an absorption maximum centered at 690 nm of unusual low amplitude. Due to these original spectral properties, the Pfr state of RtaBphP2 is switched to its Pr state regardless of the red light wavelength between 600 and 800 nm. Therefore this bacteriophytochrome acts as a simple detector of red light. Light specifically absorbed by these two bacteriophytochromes induces the ‘rod-rod’ division. Based on these results, we propose that a ‘cyst-cyst’ division occurs in the desert when water is available in the form of dew at the end of the night (dark conditions). At sunrise (red light conditions), ‘rod-rod’ divisions are induced for escaping the sun brightness. For those cells exposed to strong illumination and dryness, blue light inhibits cell division and induces the cysts resistant to desiccation.