Temperature Driven Membrane Lipid Adaptation in Glacial Psychrophilic Bacteria.

Noor Hassan,Muhammad Rafiq,Alexandre M Anesio,Jens Holtvoeth,Aamer Ali Shah,Abdul Haleem,Fariha Hasan,Ian Bull

doi:10.3389/fmicb.2020.00824

Abstract

Bacteria inhabiting non-polar glaciers are exposed to large variations in temperature, which significantly affects the fluidity of bacterial cell membranes. In order to maintain normal functions of the cell membranes, psychrophilic bacteria adapt by changing the composition of cell membrane fatty acids. However, information on the exact pattern of cell membrane adaptability in non-polar low-temperature habitats is scarce. In the present study, 42 bacterial strains were isolated from the Ghulmet, Ghulkin, and Hopar glaciers of the Hunza Valley in the Karakoram Mountain Range, Pakistan and their cell membrane fatty acid distributions studied, using gas chromatography/mass spectrometry (GC-MS) for the analysis of fatty acid methyl esters (FAMEs) liberated by acid-catalyzed methanolysis. Furthermore, Gram-negative and Gram-positive groups were grown under different temperature settings (5, 15, 25, and 35°C) in order to determine the effect of temperature on cell membrane (CM) fatty acid distribution. The analyses identified the major groups of cell membrane fatty acids (FA) as straight-chain monounsaturated fatty acids (n-MUFAs) and branched fatty acids (br-FAs), accounting for more than 70% of the fatty acids analyzed. The distribution of br-FAs and n-FAs in bacterial cell membranes was significantly affected by temperature, with the level of br-FAs decreasing relative to n-FAs with increasing temperature. Notably, the production of polyunsaturated fatty acids (PUFAs) was only seen at lower temperatures. This study contributes to understanding, for the first time, the role of br-FAs in the maintenance of cell membrane fluidity of bacteria inhabiting non-polar habitats.

Highlights

By far, the largest part of the biosphere on Earth, which includes the oceans, is exposed to temperatures below 5◦ C either perennially or seasonally (Margesin et al, 2007; Margesin and Miteva, 2011; Hoshino and Matsumoto, 2012)
The current study aims to characterize the cell membrane fatty acid profiles of Gram-positive and Gram-negative psychrotolerant bacteria isolated from non-polar glaciers and determine the role of saturated and unsaturated, straight and branched chain fatty acids (BCFA) in bacterial adaptation to low temperatures
Fatty acid distributions in bacterial cell membranes are significantly affected by growth temperature

Summary

Introduction

The largest part of the biosphere on Earth, which includes the oceans, is exposed to temperatures below 5◦ C either perennially or seasonally (Margesin et al, 2007; Margesin and Miteva, 2011; Hoshino and Matsumoto, 2012). Bacteria inhabiting cold environments face prolonged frigid temperatures and daily freeze-thaw cycles (Montiel, 2000) They have to cope with special challenges to thrive under subzero temperatures, such as slow chemical reaction rates and limited enzyme activity, denaturation of proteins, increased water viscosity, decreased cell membrane fluidity (Russell, 1990; Crowe et al, 1992; Hassan et al, 2016) and limited water availability as a solvent for biochemical reactions (Wynn-Williams, 1990). Bacteria have remarkable adaptive abilities that enable them to survive harsh and highly variable environmental conditions, including changes in pH and temperature (Ganzert et al, 2011; Bajerski and Wagner, 2013) These adaptation mechanisms include the expression of heat/cold shock proteins, production of protective compatible solutes or an altered metabolism (Georlette et al, 2004). Another strategy employed by bacteria is the modification of the cell membrane structure as it is involved in important metabolic processes and is a vital interface in the electron transport chain (Denich et al, 2003)

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Discussion

Conclusion