Structural and physiological adaptations of soil microorganisms to freezing revealed by position-specific labeling and compound-specific 13C analysis
Structural and physiological adaptations of soil microorganisms to freezing revealed by position-specific labeling and compound-specific 13C analysis
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DOI：
10.1007/s10533-019-00558-5
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发表时间：
2019-03-01
期刊：
影响因子：
4
通讯作者：
Dippold, Michaela A.
中科院分区：
文献类型：
--
作者：
Bore, Ezekiel K.;Halicki, Sara;Dippold, Michaela A.
耐冷微生物对于碳循环和生物技术应用至关重要。尽管如此，它们在冰冻环境中生存和发挥作用的机制仍不清楚。为了阐明微生物细胞膜对冷冻的适应，我们在 +5（对照）、-5 和 -20 摄氏度下用位置特异性 C-13 标记的葡萄糖孵育土壤，并定量 CO2 和磷脂脂肪酸中的 C-13。葡萄糖 C-1 在 +5 摄氏度下的高氧化揭示了通过戊糖磷酸途径的转化。然而，在零度以下的温度下，C-4 位的优先氧化表明转向糖酵解。在-5°C 下培养的土壤中，革兰氏阴性磷脂脂肪酸增加了三倍，同时 C-13 掺入量也增加了两倍。磷脂脂肪酸和掺入的 C-13 的这种不均匀增加可以通过现有脂肪酸链的同时去饱和和单不饱和脂肪酸的从头合成来解释，这表明微生物的生长。相比之下，革兰氏阳性细菌在-20℃时将其磷脂脂肪酸中的C-13含量比在-5℃和+5℃时高出2倍，而其脂肪酸含量却没有显着增加。这反映了在-20摄氏度下受损膜的强化修复而没有微生物生长。零下温度下的真菌/细菌比率比 +5 摄氏度时低 1.5 倍，反映了微生物群落结构向细菌的转变。因此，土壤微生物通过以下方式适应冷冻：（1）将其代谢途径从磷酸戊糖途径转换为糖酵解，（2）通过去饱和修饰磷脂脂肪酸，以及（3）通过减少真菌种群将微生物群落结构转向革兰氏阴性菌。
Psychrotolerant microbes are crucial for carbon cycling and biotechnological applications. Nonetheless, the mechanisms enabling their survival and functioning in frozen environments remain unclear. To elucidate adaptations of microbial cell membranes to freezing, we incubated soils with position-specific C-13 labeled glucose at +5 (control), -5 and -20 degrees C and quantified C-13 in CO2 and phospholipid fatty acids. High oxidation of glucose C-1 at +5 degrees C revealed a transformation via the pentose phosphate pathway. At subzero temperatures, however, the preferential oxidation of C-4 position suggested a switch to glycolysis. The threefold increase of Gram-negative phospholipid fatty acids in soil incubated at -5 degrees C was accompanied by a twofold increase in C-13 incorporation. This unequal increase of phospholipid fatty acids and incorporated C-13 can be explained by simultaneous desaturation of existing fatty acid chains and the de novo synthesis of monounsaturated fatty acids, which indicates microbial growth. In contrast, Gram-positive bacteria incorporated 2 times higher C-13 into their phospholipid fatty acids at -20 degrees C than at -5 and +5 degrees C without a significant increase in their fatty acid contents. This reflects intensive repair of membranes damaged at -20 degrees C without microbial growth. The fungal/bacterial ratio was 1.5 times lower at subzero temperatures than at +5 degrees C, reflecting a shift in microbial community structure towards bacteria. Accordingly, soil microorganisms adapted to freezing by (1) switching their metabolic pathway from the pentose phosphate pathway to glycolysis, (2) modifying phospholipid fatty acids by desaturation and, (3) shifting microbial community structure towards Gram-negative bacteria by reducing the fungal population.