Stress response physiology of thermophiles
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MINI-REVIEW
Stress response physiology of thermophiles Preeti Ranawat1 · Seema Rawat1
Received: 19 August 2016 / Revised: 7 December 2016 / Accepted: 16 December 2016 © Springer-Verlag Berlin Heidelberg 2017
Abstract Thermo (or hyperthermo) philic microorganisms are ubiquitous having a wide range of habitats from freshly fallen snow to pasteurized milk to geothermal areas like hot springs. The variations in physicochemical conditions, viz., temperature, pH, nutrient availability and light intensity in the habitats always pose stress conditions for the inhabitants leading to slow growth or cell death. The industrial processes used for harvesting secondary metabolites such as enzymes, toxins and organic acids also create stressed environments for thermophiles. The production of DNA-binding proteins, activation of reactive oxygen species detoxification system, compatible solute accumulation, expression of heat shock proteins and alterations in morphology are a few examples of physiological changes demonstrated by these microscopic lifeforms in stress. These microorganisms exhibit complex genetic and physiological changes to minimize, adapt to and repair damage caused by extreme environmental disturbances. These changes are termed as ‘stress responses’ which enable them to stabilize their homeostasis. The exploration of important thermophilic factors would pave the way in engineering the microbial strains for various biotechnological applications. This review article presents a picture of physiological responses of thermophiles against various stress conditions as their mechanisms to respond to stress make them model organisms to further explore them for basic and applied biology purposes. Communicated by Yusuf Akhter. * Seema Rawat [email protected] 1
Department of Botany and Microbiology, Hemvati Nandan Bahuguna Garhwal University, Srinagar (Garhwal), Uttrakhand, India
Keywords Thermophiles · Hyperthermophiles · Stress · Enzymes · Toxins · Organic acids
Introduction Extremophiles thrive in extreme ecosystems which may have either extremely high or low pH, high or low temperatures, high salinity, high pressure and various combinations thereof. Extremophilic microorganisms include members of all three domains of life, Archaea, Bacteria and Eukarya (Robb et al. 2008). As prokaryotes are ubiquitous because of their small size, easy dispersal and metabolic versatility, utilization of broad range of nutrients and ability to tolerate unfavorable environmental conditions, they form a major component of most of the ecosystems (Kumar et al. 2014). Many investigations are focused on the potential of extremophiles as sources of highly active enzymes ‘extremozymes’ and other products such as antibiotics and compatible solutes (Robb et al. 2008). Major attention worldwide is being drawn by thermophiles (i.e., organisms with optimum growth temperature 50–80 °C) and hyperthermophiles (i.e., organisms that grow optimally at or above 80 °C) (Holden 2012). Thermophiles include bacteria like Geobacillus stereothermop
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