Light on the cell cycle of the non-photosynthetic bacterium Ramlibacter tataouinensis

Abstract

Ramlibacter tataouinensis TTB310, a non-photosynthetic betaproteobacterium isolated from a semi-arid region of southern Tunisia, forms both rods and cysts. Cysts are resistant to desiccation and divide when water and nutrients are available. Rods are motile and capable of dissemination. Due to the strong correlation between sunlight and desiccation, light is probably an important external signal for anticipating desiccating conditions. Six genes encoding potential light sensors were identified in strain TTB310. Two genes encode for bacteriophytochromes, while the four remaining genes encode for putative blue light receptors. We determined the spectral and photochemical properties of the two recombinant bacteriophytochromes RtBphP1 and RtBphP2. In both cases, they act as sensitive red light detectors. Cyst divisions and a complete cyst-rod-cyst cycle are the main processes in darkness, whereas rod divisions predominate in red or far-red light. Mutant phenotypes caused by the inactivation of genes encoding bacteriophytochromes or heme oxygenase clearly show that both bacteriophytochromes are involved in regulating the rod-rod division. This process could favor rapid rod divisions at sunrise, after dew formation but before the progressive onset of desiccation. Our study provides the first evidence of a light-based strategy evolved in a non-photosynthetic bacterium to exploit scarse water in a desert environment.

No Light, No Germination: Excitation of the Rhodospirillum centenum Photosynthetic Apparatus Is Necessary and Sufficient for Cyst Germination

“…This indicates that the tested photoreceptors are not responsible for light-induced germination of R. centenum cysts. This is unlike the nonphotosynthetic bacterium Ramlibacter tataouinensis , where the switch between the cyst and vegetative states is controlled by photoreceptors ( 25 ).…”

“…Finally, the nonphotosynthetic betaproteobacterium Ramlibacter tataouinensis has two red-light-sensitive bacteriophytochromes that regulate the switch between rod-shaped vegetative cells and desiccation-resistant cyst cells. In this species, darkness favors cyst formation, while far-red light favors vegetative cell formation ( 25 ). Therefore, we addressed whether light excitation of photoreceptors could also function as a germination signal for R. centenum .…”

Growth promotion of a deep‐sea bacterium by sensing infrared light through a bacteriophytochrome photoreceptor

“…Our data reveal that bacteriophytochrome CmoBphp can perceive different wavelengths of light though its N‐terminal light‐sensory domains and integrates the light signal to the downstream cellular processes. Due to the extreme growing conditions of strain OT19 in the deep sea, CmoBphp may present unusual photochemical properties, as already observed for several other bacteriophytochromes (Giraud and Verméglio, 2008; De Luca et al ., 2019). We therefore expressed and purified recombinant holo‐CmoBphp of strain OT19 to determine the spectral characteristics.…”

Bio-Organic Fertilizers Manipulate Abundance Patterns of Rhizosphere Soil Microbial Community Structure To Improve Tomato Productivity

“…While non-photosynthetic, Ramlibacter, an aerobic, chemo-organotrophic, beta-proteobacterial genus, have been isolated from garden, forest soil, and even dry conditions of desert environments, suggesting its extensive environmental adaptability. (De Luca et al, 2019;Akter et al, 2020). Sphingomonas, a gram-negative, rodshaped, chemoheterotrophic, strictly aerobic bacteria, has the ability to survive in low concentrations of nutrients, as well as to metabolize a wide variety of carbon sources.…”