Photosynthetic Microbes: Evolution, Classification, and Structural Physiology

Photosynthesis converts carbon dioxide and water into organic molecules and oxygen by using light energy and provides the basic building blocks for all the life on Earth. It takes place in chloroplasts of green plants, cyanobacteria, and algae. The chlorophyll pigment in chloroplasts absorbs light energy, which is then used to split water molecules into oxygen and hydrogen ions. The hydrogen ions are used to generate ATP, which provides energy for the synthesis of glucose from carbon dioxide through Calvin cycle. Other than Calvin cycle, there exists different routes including reverse Krebs cycle, and 3-hydroxypropionate-4-hydroxybutyrate cycle through which carbon fixation occurs in certain bacteria and archaea. These cycles have potential applications in biotechnology and bioengineering to produce biofuels and other bioproducts. Cyanobacteria and microalgae are unicellular photosynthetic microbes belonging to diverse taxonomical groups. Nevertheless, there are certain similarities between the two groups, for instance in pigment biosynthesis and functioning of photosystem complexes. Studying the photosynthetic physiology in these microbes provides crucial insights into the evolution of oxygenic photosynthesis in higher plants and its practical implications. Their ability to grow in unfavorable conditions and to utilize waste resources made them valuable industrial cell factories. The chapter highlights the photosynthetic microbes and their cellular structure and their complexity for photosynthesis process.