Stress response physiology of thermophiles

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.

Introducing the Newly Isolated Bacterium Aneurinibacillus sp. H1 as an Auspicious Thermophilic Producer of Various Polyhydroxyalkanoates (PHA) Copolymers–1. Isolation and Characterization of the Bacterium

“…The term "thermophiles" is devoted to microorganisms revealing optimal growth temperature above 45 • C [1]. Actually, these microbes are ubiquitous since they can be isolated from a wide range of habitats from freshly fallen snow to pasteurized milk to geothermal areas like hot springs [2]. Currently, thermophiles attract attention of industrial biotechnologists since bioprocesses operated at elevated temperatures have a number of advantages, including a reduced risk of microbial contamination, lowered jeopardy by phage infection, improved solubility of substrates such as polysaccharide-rich resources, continuous and direct recovery of volatile metabolites from fermentation broth such as alcohols or volatile fatty acids (VFAs) and decreased cooling costs and demands for cooling water due to the higher temperature difference between bioreactor and the ambient air.…”

Heat Shock Proteins in the “Hot” Mitochondrion: Identity and Putative Roles

“…Typically, when micro‐organisms are heat‐stressed they evoke a variety of physiological responses, including the production of DNA‐binding proteins, upregulation of the reactive oxygen species (ROS) detoxification system, solute accumulation, and the expression of heat shock proteins (Hsps), to name a few . Since mitochondria appear to be operating at an elevated temperature, relative to the cytosol, the question of whether similar protective mechanisms are operating within mitochondria arises.…”

“…Typically, when micro-organisms are heat-stressed they evoke a variety of physiological responses, including the production of DNA-binding proteins, upregulation of the reactive oxygen species (ROS) detoxification system, solute accumulation, and the expression of heat shock proteins (Hsps), to name a few. [4] Since mitochondria appear to be operating at an elevated temperature, relative to the cytosol, the question of whether similar protective mechanisms are operating within mitochondria arises. Interestingly, bulk differential scanning calorimetry studies on cellular organelles, including the cytosol and mitochondria, revealed melting temperatures (T m values) of ≈40°C, suggesting that, on average, thermolabile proteins appear to be present in all cellular organelles and compartments.…”

Extremophiles, a Nifty Tool to Face Environmental Pollution: From Exploitation of Metabolism to Genome Engineering

“…Sometimes the same microorganism owns more metal resistance mechanisms; for example, Escherichia coli possesses either a copper active transport system (CopA) and another system based on multicopper oxidases (CueO) and CusCFBA transport system for periplasmic copper detoxification [ 23 , 44 ]. These resistance mechanisms are often activated as stress response [ 45 , 46 ]; understanding their underpinning molecular basis is crucial for application in the environmental monitoring of metal contamination (biosensing) and/or to set up bioremediation processes [ 14 , 47 , 48 ].…”