Physiological investigation of Rhodobacter sphaeroides

Abstract

Rhodobacter sphaeroides is an ?-3 purple non-sulfur eubacterium with an extensive metabolic organization. Under anaerobic conditions it is able to grow by performing photosynthesis, respiration and fermentation. Photosynthesis occurs only under anaerobic conditions since photosynthetic apparatus of R. sphaeroides is harmed in the presence of oxygen. Photosynthesis may be both photoheterotrophic and photoautotrophic. While R. sphaeroides performs photoheterotrophic photosynthesis using organic compounds as both a carbon and a reducing source, R. sphaeroides performs photoautrophic photosynthesis using carbon dioxide as the sole carbon source and hydrogen as the source of reducing power. In addition, R. sphaeroides can grow both chemoheterotrophically and chemoautotrophically. Regarding biotechnology applications, R. sphaeroides is used both in industry and in medicine. Industrial application of R. sphaeroides comprises hydrogen gas and polyhydroxybutyrate (PHB) production and bioremediation of heavy metals. R. sphaeroides can also be used in the production of vitamin B12, coenzyme Q10, 5-aminolevulinic acid (ALA) and porphyrin. Like other microorganisms, R. sphaeroides has different defence mechanisms to give response against different stress types that occurs frequently in its microenvironment. Defence mechanisms of R. sphaeroides vary according to the types of stress. For instance, while under osmotic stress condition, R. sphaeroides gives response by increasing cardiopilin levels which is an anionic phospholipid playing an important role in energy conversion in cells of R. sphaeroides, as for, under oxidative stress condition it gives response increasing its carotenoid levels.