ABSTRACT
Nitrogen-fixers or diazotrophs have been used in agriculture as biofertilizer since antiquity. Among them, cyanobacteria (CB), the diverse group of gram-negative prokaryotes has evolved to carry out photosynthesis and nitrogen fixation simultaneously and contributes maximally to the global nitrogen cycle. Development of heterocysts in CB under nitrogen limiting conditions has been divided into three stages that include Early Proheterocysts, Proheterocysts, and Mature heterocysts. The middle stage of heterocyst differentiation is marked by structural and physiological changes that are regulated by many genes. Many iron-containing substances are needed for important biological pathways like catabolic and metabolic pathways, assimilation of nitrogen, and transport of electrons and production of chlorophyll a. Nitrogen is an important nutrient that affects the yield of crops. Biologically reactive nitrogen is hence regularly supplied to crops in the form of artificial nitrogen fertilizer. In the developed world, the extensive use of these fertilizers in agriculture has added a significant financial and environmental burden.
