The metabolic pathways of polyhydroxyalkanoates and exopolysaccharides synthesized by Haloferax mediterranei in response to elevated salinity
The metabolic pathways of polyhydroxyalkanoates and exopolysaccharides synthesized by Haloferax mediterranei in response to elevated salinity
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Haloferax mediterranei 响应高盐度合成的聚羟基脂肪酸酯和胞外多糖的代谢途径
DOI：
10.1016/j.jprot.2020.104065
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发表时间：
2021-02-10
影响因子：
3.3
通讯作者：
Cui, You-Wei
中科院分区：
文献类型：
--
作者：
Pacholak, Amanda;Gao, Ze-Liang;Cui, You-Wei
如何动员或激活聚合物合成作为地中海盐黄菌对高渗条件的生物反应仍未被广泛探索。本研究采用等压标签相对和绝对定量（iTRAQ）技术研究了地中海海鳗在高盐度环境下的蛋白表达。发酵结束时，在75和250 g L-1 NaCl浓度下收获微生物。在鉴定的2123个蛋白中，170个蛋白存在差异表达。基因本体注释显示，在生物过程类中注释的蛋白质数量最多，这类蛋白质负责代谢过程、细胞成分和催化活性。差异表达蛋白属于对刺激的反应类，也属于催化活性和结合类。在高盐度条件下，PHA和EPS的生成主要通过三条途径响应高渗压力。两种过表达的蛋白，β -酮酰基- acp还原酶和3-羟基酰基-辅酶a脱氢酶，促进了pha的合成。丝氨酸-丙酮酸转氨酶和丝氨酸-乙醛酸转氨酶被上调，从而增加了葡萄糖向PHA的转化。硫酸腺苷酸转移酶和硫酸腺苷酸激酶水平下调可导致EPS合成减少。本研究有助于更好地了解合成的聚合物抗盐胁迫的蛋白质组学机制。意义：地中海盐腐菌（Haloferax mediterranei）是嗜盐古菌家族的一员，以其发酵生产聚β -羟基烷酸酯（pha）而闻名。pha是一种具有广泛应用潜力的天然聚合物，是石油基塑料和生物相容性材料的良好替代品。几十年来，地中海海蝇合成的pha的功能作用被认为是碳和能量储备。这一发现证明，暴露于高盐度环境下的地中海海蝇产生PHA和EPS的差异是由蛋白表达差异引起的。本文首次报道了地中海古菌合成的PHA和EPS在盐度升高时是如何被动员起来的，有助于了解嗜盐古菌对高渗胁迫的反应和发酵生产的精确控制。尽管它具有作为PHA细胞工厂的优势，但H. mediterranei同时合成EPS，从而降低了PHA生产的最大产量。总的来说，盐度可以作为重要的微生物发酵参数，在工业发酵中获得最高的PHA产量，以及最低的EPS合成。
How polymer synthesis is mobilized or activated as a biological response of Haloferax mediterranei against hypertonic conditions remains largely unexplored. This study investigated the protein expression of H. mediterranei in response to high salinity by using isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomic analysis. The microbes were harvested at end of fermentation at the NaCl salinity of 75 and 250 g L-1. Among the identified 2123 proteins, 170 proteins were differentially expressed. Gene ontology annotation revealed that the highest number of proteins was annotated in biological process category, which was responsible for metabolic process, cellular component and catalytic activity. Differentially expressed proteins were belonged to the class of response to stimulus as well as catalytic activity and binding. Under high salinity conditions, three pathways were established as key responses of PHA and EPS production to hypertonic pressure. Two overexpressed proteins, beta-ketoacyl-ACP reductase and 3-hydroxyacyl-CoA dehydrogenase, enhanced the synthesis of PHAs. The serine-pyruvate transaminase and serine-glyoxylate transaminase were upregulated, thereby increasing the conversion of glucose to PHA. Downregulated levels of sulfate-adenylyl transferase and adenylyl-sulfate kinase could cause diminished EPS synthesis. This study could contribute to better understanding of the proteomic mechanisms of the synthesized polymers in defending against salt stress.Significance: Haloferax mediterranei, a family member of halophilic archaea, is well known for its fermentative production of poly-beta-hydroxyalkanoates (PHAs). PHAs are natural polymers that exhibit great potential in a wide range of applications such as a good alternative to petroleum-based plastics and the biocompatible material. For decades, the functional role of PHAs synthesized by H. mediterranei is deemed to be carbon and energy reservations. The finding proved that differential production of PHA and EPS in H. mediterranei exposed to elevated salinity was caused by differential protein expression. This is the first report on how PHA and EPS synthesized by H. mediterranei is mobilized as the response of increased salinity, contributing to the understanding of halophilic archaea's response to hypertonic stress and the precise control of fermentation production. Despite its advantages as a PHA cell factory, H. mediterranei synthesized EPS simultaneously, thereby lowering the maximum yield of PHA production. Overall, salinity can be used as a vital microbial fermentation parameter to obtain the highest harvest of PHA, as well as the lowest EPS synthesis in industrial fermentation.