Fig. 2: Porphyrobacter sp. ULC335 presents rhythmic growth patterns in stationary phase that are dependent on functional anoxygenic phototrophy.

A Rhythmic variations in optical density (measured at 680 nm) of three replicate cultures of Porphyrobacter sp. ULC335 under dark-light alternance (light at 180 µmol/s/cm²). Light intensity, culture temperature (water bath), and room temperature are shown as evidence that density changes are from biological and not technical origin. Cultures were maintained in 80 ml tubes in a device adapted for the culture of cyanobacteria or algae. The rhythms do not present persistence under continuous light (120 h–156 h) or continuous darkness (204 h–240 h), and follow light variation seamlessly when the period is shorter than 24 h (240 h–288 h). B Colony phenotype of Porphyrobacter sp. ULC335 (B⁺C⁺) and four transposon mutants grown on BG11-P-agar in the dark. The color of colonies are in agreement with the absorbance profiles of liquid cultures (Suplementary Fig. 12). C Simplified pathway of carotenoid and bacteriochlorophyll a biosynthesis. In red, the genes in which the transposon is inserted for each of the mutant strains. Ticked lines represent multiple synthesis steps (enzymatic reactions) or multiple convergent effects (regulators). D Rhythmic variations in optical density (measured at 680 nm) of the wild type compared with the bacteriochlorophyll a and carotenoid overproducer strain. No significant difference in pattern is apparent between the two strains. The culture conditions are similar to (A). E Variations in optical density (OD, measured at 680 nm) of the wild type compared with the three bacteriochlorophyll a and/or carotenoid mutant strains. B⁻C⁺ and B⁻C⁻ did not present any rhythmic growth pattern; B⁺C⁻ presented slight variations in slope between dark and light phases, the speed of the OD decline increasing during light phases. Because B⁺C⁻ was strongly inhibited by light, the cultures were maintained under continuous darkness until stationary phase, when a 12 h/12 h dark-light alternance illumination regime was started.