Cereibacter sphaeroides

Cereibacter sphaeroides (previously Rhodobacter sphaeroides) is a species of purple bacteria capable of generating energy through photosynthesis. It grows best under anaerobic phototrophic conditions, including both photoheterotrophic and photoautotrophic modes, and under aerobic chemoheterotrophic conditions in the absence of light. C. sphaeroides is also able to fix nitrogen. It is remarkably metabolically diverse, as it is able to grow heterotrophically via fermentation, as well as aerobic and anaerobic respiration. This metabolic versatility has made C. sphaeroides a subject of interest as a microbial cell factory for various biotechnological applications.

Cereibacter sphaeroides has been isolated from deep lakes and stagnant waters.

Cereibacter sphaeroides is a model organism for the study of bacterial photosynthesis. It grows under standard laboratory conditions and exhibits high photosynthetic efficiency. The regulation of its photosynthetic machinery is a significant research focus, as C. sphaeroides possesses an intricate system for sensing O₂ tension. In response to reduced oxygen tension, the organism forms invaginations in its cytoplasmic membrane that house the photosynthetic apparatus. These structures, known as chromatophores, play a key role in light-driven energy generation.

The genome of C. sphaeroides is also notable for its complexity. It has two circular chromosomes, one of 3 Mb (CI) and one of 900 Kb (CII), and five native plasmids. Although many genes are duplicated between CI and CII, they appear to be differentially regulated. Numerous open reading frames (ORFs) on CII encode proteins of unknown function. Disruption of these genes frequently leads to various types of auxotrophy, suggesting that CII is functionally distinct and not a truncated version of CI.