Hassan Noor, Anesio Alexandre M, Rafiq Muhammad, Holtvoeth Jens, Bull Ian, Haleem Abdul, Shah Aamer Ali, Hasan Fariha
Applied Environmental and Geomicrobiology Laboratory, Department of Microbiology, Quaid-i-Azam University, Islamabad, Pakistan.
Bristol Glaciology Centre, School of Geographical Sciences, Faculty of Science, University of Bristol, Bristol, United Kingdom.
Front Microbiol. 2020 May 14;11:824. doi: 10.3389/fmicb.2020.00824. eCollection 2020.
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 (-MUFAs) and branched fatty acids (-FAs), accounting for more than 70% of the fatty acids analyzed. The distribution of br-FAs and -FAs in bacterial cell membranes was significantly affected by temperature, with the level of br-FAs decreasing relative to -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.
栖息于非极地冰川的细菌会面临温度的大幅变化，这会显著影响细菌细胞膜的流动性。为了维持细胞膜的正常功能，嗜冷细菌会通过改变细胞膜脂肪酸的组成来进行适应。然而，关于非极地低温栖息地中细胞膜适应性的确切模式的信息却很匮乏。在本研究中，从巴基斯坦喀喇昆仑山脉罕萨山谷的古尔梅特、古尔金和霍帕尔冰川中分离出42株细菌菌株，并对其细胞膜脂肪酸分布进行了研究，采用气相色谱/质谱联用仪（GC-MS）分析酸催化甲醇解释放的脂肪酸甲酯（FAMEs）。此外，革兰氏阴性菌和革兰氏阳性菌群体在不同温度设置（5、15、25和35°C）下培养，以确定温度对细胞膜（CM）脂肪酸分布的影响。分析确定细胞膜脂肪酸（FA）的主要类别为直链单不饱和脂肪酸（-MUFAs）和支链脂肪酸（-FAs），它们占所分析脂肪酸的70%以上。温度对细菌细胞膜中br-FAs和-FAs的分布有显著影响，随着温度升高，br-FAs的水平相对于-FAs下降。值得注意的是，多不饱和脂肪酸（PUFAs）仅在较低温度下产生。本研究首次有助于理解br-FAs在维持栖息于非极地栖息地细菌细胞膜流动性中的作用。
