Rhoospirillum rubrum (R. rubrum) is a Gram-negative, purple-colored Proteobacterium, having a size of 800 to 1000 nanometer. As it can live both anaerobically and aerobically, it is therefore both heterotrophic and autotrophic. Under aerobic growth photosynthesis is genetically suppressed and R. rubrum is then colorless. After the exhaustion of oxygen, R. rubrum immediately starts the production of photosynthesis apparatus including membrane proteins, bacteriochlorophylls and carotenoids, i.e. the bacterium becomes photosynthesis active. The repression mechanism for the photosynthesis is poorly understood. The photosynthesis of R. rubrum differs from that of plants as it possesses not chlorophyll a, but bacteriochlorophylls. While bacteriochlorophyll a absorbs light having a maximum frequency of 800 to 925 nm, chlorophyll absorbs light having a maximum frequency of 660 to 680 nm. R. rubrum is a spiral-shaped bacterium (spirillum, plural form: spirilla). R. rubrum is interesting for biotechnology: 1) Quantitative accumulation of PHB (poly-hydroxy-butric-acid) precursors in the cell for the production of biological plastic, 2) production of biological hydrogen fuel and 3) model system for studying the conversion from light energy to chemical energy.