Actinomycetes benefaction role in soil and plant health Asma Absar Bhatti, Shamsul Haq, Rouf Ahmad Bhat * Division of Environmental Sciences, Sher-e-Kashmir University of Agricultural Sciences and Technology, Kashmir,190025, India article info Article history: Received 21 May 2017 Received in revised form 13 September 2017 Accepted 14 September 2017 Available online 18 September 2017 Keywords: Actinomycetes Soil health Nitrogen fixation Biological control Enzymes abstract Actinomycetes are aerobic, spore forming gram-positive bacteria, belonging to the order actinomycetales characterized with substrate and aerial mycelium growth. They are the most abundant organisms that form thread-like filaments in the soil and are responsible for characteristically “earthy” smell of freshly turned healthy soil. They play major roles in the cycling of organic matter; inhibit the growth of several plant pathogens in the rhizosphere and decompose complex mixtures of polymer in dead plant, animal and fungal material results in production of many extracellular enzymes which are conductive to crop production. The major contribution in biological buffering of soils, biological control of soil environments by nitrogen fixation and degradation of high molecular weight compounds like hydrocarbons in the polluted soils are remarkable characteristics of actinomycetes. Besides this, they are known to improve the availability of nutrients, minerals, enhance the production of metabolites and promote plant growth regulators. Furthermore, actinobacteria do not contaminate the environment instead, they help sus- tainably in improving soil health by formation and stabilization of compost piles, formation of stable humus and combine with other soil microorganisms in breaking down the tough plant residues such as cellulose and animal residues to maintain the biotic equilibrium of soil by cooperating with nutrient cycling. © 2017 Elsevier Ltd. All rights reserved. Contents 1. Introduction ...................................................................................................................... 459 2. Nature and habitat ................................................................................................................ 459 2.1. Terrestrial habitat ........................................................................................................... 459 2.2. Aquatic habitat .............................................................................................................. 459 2.2.1. Fresh water habitat ................................................................................................... 459 2.2.2. Marine habitat ....................................................................................................... 459 2.3. Extreme environments ....................................................................................................... 460 3. Structure ......................................................................................................................... 460 4. Role of actinomycetes in soil and plant health ......................................................................................... 460 4.1. Mechanism of organic acid production ............................................... ......................................... 460 4.2. Nitrogen fixation ............................................................................................................ 461 4.3. Decomposition of organic matters .................................................. ........................................... 461 4.4. Actinomycetes as plant growth promoting bacteria .......................................... .................................... 462 4.5. Production of plant growth regulators .......................................................................................... 462 4.6. Siderophores production ...................................................................................................... 462 4.7. Actinomycetes as plant growth promoting agents .......................................... ..................................... 462 4.8. Actinomycetes as biocontrol tools .................................................. ........................................... 462 4.9. Actinomycetes as production of plant growth hormone (indole-3-acetic acid) ....................................................... 462 4.10. Actinomycetes in biocorrosion ............................................................................................... 463 4.11. Actinomycetes enzymes ...................................................................................................... 463 * Corresponding author. E-mail address: rufi.bhat@gmail.com (R.A. Bhat). Contents lists available at ScienceDirect Microbial Pathogenesis journal homepage: www.elsevier.com/locate/micpath http://dx.doi.org/10.1016/j.micpath.2017.09.036 0882-4010/© 2017 Elsevier Ltd. All rights reserved. Microbial Pathogenesis 111 (2017) 458e467