NITROGEN CYCLE

PANKAJ Microbiology

CONTENTS

INTRODUCTIONMAJOR MICROBIAL NITROGEN

TRANSFORMATIONMECHANISM OF NITROGEN CYCLE BY

ENZYMEROLE OF ELECTRON IN NITROGEN CYCLENif GENESDEFIENCY SYMPTOMS

INTRODUCTIONThe nitrogen cycle is the process by which

nitrogen is converted between its various chemical forms. This transformation can be carried out via both biological and non-biological processes. Important processes in the nitrogen cycle include fixation, mineralization, nitrification, and denitrification. The majority of Earth's atmosphere (approximately 78%) is nitrogen.

MAJOR MICROBIAL N2 TRANSFORMATIONNitrogen fixationNitrificationDenitrificationAnammoxAmmonification

NITROGEN FIXATION Atmospheric nitrogen by nitrogen fixing bacteria

to yield ammonia.N2+8H =NH3+H2 ( Cynobacteria)

NITRIFICATION The atmospheric nitrogen is fixed by

nitrogen fixing bacteria to yield ammonia. This ammonia is used by living microorganism and converted into nitrate.

NH4+ = NO2

- ( Nitrosomonas)

NO2- = NO3

- ( Nitrobactor)

Denitrification The conversion of nitrate to nitrogen under

anaerobic condition is known as denitrification.

NO3- = N2 (Bacillus, Prococus,

pseudomonas)

ANAMMOXIn this biological process, nitrite and

ammonium are converted directly into dinitrogen gas. This process contributes up to 50% of the dinitrogen gas produced in the oceans. It is thus a major sink for fixed nitrogen and so limits oceanic primary productivity. The overall catabolic reaction is:

NH4+ + NO2

− → N2 + 2H2O. (Brocadia)The bacteria that perform the anammox

process belong to the bacterial phylum planctomycetes of which Planctomyces and Pirellula are the best known genera.

AMMONIFICATION Ammonia Is released during the decomposition of

organic nitrogen compound such as amino acids and nucleotides a process called ammonification.

Organic N2 =NH4+ ( Rhizobium)

Nitrogenase complex1. Dinitrogenase reductase2.Dinitrogenase

Nif Genes The nif gene is the gene responsible for the

coding of proteins related and associated with the fixation of atmospheric nitrogen into a form of nitrogen available to plants. These genes are found in nitrogen fixing bacteria and cyanobacteria.

DEFICIENCY SYMPTOMSChlorosis appears in older leaves.Dormancy of lateral buds .Delaying of flowering .

Reference Burford, J.R., and J.M. Bremner. 1975. Relationships between

the denitrification capacities of soils and total, water-soluble and readily decomposable soil organic matter. Soil Biochem. 7:389-394

Marschner, H. 1995. Mineral Nutrition in Higher Plants. Academic Press, London.

Tisdale, S.L., W.L. Nelson, J.D. Beaton, and J.L. Havlin. 1993. Soil Fertility and Fertilizers. MacMillan Publishing Co., New York, N.Y.

Brock 8th edition . Nitrogen cycle.page 532Lehninger fourth edition.nitrogen cycle page no. 834

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