Hopanoid-free Methylobacterium extorquens DM4 overproduces carotenoids and has widespread growth impairment.
Hopanoid-free Methylobacterium extorquens DM4 overproduces carotenoids and has widespread growth impairment.
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DOI：
10.1371/journal.pone.0173323
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发表时间：
2017
期刊：
影响因子：
3.7
通讯作者：
Marx CJ
中科院分区：
文献类型：
--
作者：
Bradley AS;Swanson PK;Muller EE;Bringel F;Caroll SM;Pearson A;Vuilleumier S;Marx CJ
Hopanoids是一种甾醇类膜脂，广泛用作细菌的地球化学代用品。目前，hopanoids的生理作用还没有得到很好的理解，这是解释其存在于古代或当代沉积物中的意义的主要限制之一。先前对一系列细菌中缺乏类Hopanoids的突变体的分析揭示了在正常生长条件下的一系列表型，但大多数至少对毒素和渗透胁迫具有增加的敏感性。我们采用了扭脱甲基杆菌DM 4的无类霍帕酸菌株，在许多测试条件下，包括在没有额外应激源的正常生长条件下，发现了相对于野生型的严重生长缺陷。突变体过量产生类胡萝卜素-该菌株的另一种主要类异戊二烯产物-并显示出改变的脂肪酸分布，在液体培养基中的明显絮凝，以及比野生型菌株更低的生长产量。絮凝表型可以通过向培养基中添加纤维素酶来减轻，这表明类Hopanoids的功能与M中纤维素的分泌之间存在联系。黑曲霉DM 4.在固体培养基上，无类阿片突变株的菌落比野生型小，并且对渗透压或pH胁迫以及各种毒素更敏感。结果表明，M.扭脱体DM 4与类霍帕酸对膜流动性和脂质包装重要的假设一致，但也表明需要类霍帕酸的特定生理过程在细菌谱系中不同。我们的工作为新出现的观察结果提供了进一步的支持，即hopanoids在膜鲁棒性和屏障功能中的作用可能在整个谱系中很重要，可能通过与外膜中的脂质A的相互作用介导。
Hopanoids are sterol-like membrane lipids widely used as geochemical proxies for bacteria. Currently, the physiological role of hopanoids is not well understood, and this represents one of the major limitations in interpreting the significance of their presence in ancient or contemporary sediments. Previous analyses of mutants lacking hopanoids in a range of bacteria have revealed a range of phenotypes under normal growth conditions, but with most having at least an increased sensitivity to toxins and osmotic stress. We employed hopanoid-free strains of Methylobacterium extorquens DM4, uncovering severe growth defects relative to the wild-type under many tested conditions, including normal growth conditions without additional stressors. Mutants overproduce carotenoids–the other major isoprenoid product of this strain–and show an altered fatty acid profile, pronounced flocculation in liquid media, and lower growth yields than for the wild-type strain. The flocculation phenotype can be mitigated by addition of cellulase to the medium, suggesting a link between the function of hopanoids and the secretion of cellulose in M. extorquens DM4. On solid media, colonies of the hopanoid-free mutant strain were smaller than wild-type, and were more sensitive to osmotic or pH stress, as well as to a variety of toxins. The results for M. extorquens DM4 are consistent with the hypothesis that hopanoids are important for membrane fluidity and lipid packing, but also indicate that the specific physiological processes that require hopanoids vary across bacterial lineages. Our work provides further support to emerging observations that the role of hopanoids in membrane robustness and barrier function may be important across lineages, possibly mediated through an interaction with lipid A in the outer membrane.