Role of Blue green algae ( Cyanobacteria) in nitrogen fixation

Yashwant Sompura 

University College of Science, MLS University, Udaipur, Rajasthan-313001

 INTRODUCTION 

  Blue green algae (BGA) is also called as cyanobacteria. It belongs to cyanophyceae (Gr. Cyano= blue green) or mixophyxceae. It is blue green in colour due to presence of c-phycocyanin or c-phycoerythrin pigment and they lack of sexual reproduction such as Anabaena, Nostoc. BGA has potential of fixation of nitrogen and play a significant role in ecosystem balance. It provides nitrogen to nutrient cycle. The fixation of atmospheric nitrogen into ammonia or useful form through an organism is called as biological nitrogen fixation. These nitrogen fixing bacteria are found in the root of plant usually in leguminous plants. In blue green algae, the nitrogen fixation was firstly observed by Boilhac in 1896 in species of nostoc. In 1906, Heinze obtained evidence of nitrogen fixation in culture of Nostoc. In 1926, Molisch isolated Nostoc and concluded that they grew in a N free solution. In 1928, Drewes obtained result as Anabaena variabitis and Nostoc punctiforme grew in nitrogen free solution and fix nitrogen. It has been also reported by Copeland in 1939 that species of Oscillatoria, Spirulina labrinthiformis and Pharmidium laminosum has the capacity to fix the nitrogen. In 1935, Gerhard winter also reported that Nostoc mostly fix the nitrogen in the presence of carbohydrate and more in the dark as compare to light. 

BIOLOGICAL NITROGEN FIXATION 

It is a one of the important and essential elements for plant growth and development. It is found in the soil in abundant form. Soil loss nitrogen by means of one or more process such as addition of animal and plant manure. Through nitrogen fixation which may be either symbiotic or non-symbiotic microorganisms. It is important to increase nitrogen in soil and increase fertility of soil. It has been reported that non-symbiotic nitrogen fixation is important for desert soil. It was firstly discovered by Hermann Hellriegel (German agronomist) and Martinus Beijerinck (Dutch microbiologist). Biological nitrogen fixation is a specific process in which the atmospheric N is converted into ammonia (NH3) by means of nitrogenase enzyme. 

 N2 + 16 ATP + 8H+ +8e- ➡ 2NH3 + H2+ 16 ADP +16Pi 

 This is occurs through an microorganism which is called diazotrophs or N2 fixers. These diazotrophs may be either Blue green algae or bacteria. These are two types of biological nitrogen fixers : 1. Symbiotic : Free living nitrogen fixers found in terrestrial as well as aquatic habitat. These may be classified into following groups: Free living aerobic- Azotobacter Free living anaerobic Clostridium Blue green algae- Nostoc, Anabaena, Oscillatoria.The Azolla and Anabaena symbiosis is a mutualistic association between the water fern azolla with a diazotrophic cyanobacteria.

The algae provide nitrogen and fern provide a habitat for the algae.These bacteria having ability to convert atm.nitrogen into nitrate fertilizer. 2. Non-symbiotic.