Some microbes display pleomorphism, showing variable cell shapes in a single culture, whereas others differentiate to adapt to changed environmental conditions. The pleomorphic archaeon Haloferax volcanii commonly forms discoid-shaped ('plate') cells in culture, but may also be present as rods, and can develop into motile rods in soft agar, or longer filaments in certain biofilms. Here we report improvement of H. volcanii growth in both semi-defined and complex media by supplementing with eight trace element micronutrients. With these supplemented media, transient development of plate cells into uniformly shaped rods was clearly observed during the early log phase of growth; cells then reverted to plates for the late log and stationary phases. In media prepared with high-purity water and reagents, without supplemental trace elements, rods and other complex elongated morphologies ('pleomorphic rods') were observed at all growth stages of the culture; the highly elongated cells sometimes displayed a substantial tubule at one or less frequently both poles, as well as unusual tapered and highly curved forms. Polar tubules were observed forming by initial mid-cell narrowing or tubulation, causing a dumbbell-like shape, followed by cell division towards one end. Formation of the uniform early log-phase rods, as well as the pleomorphic rods and tubules were dependent on the function of the tubulin-like cytoskeletal protein, CetZ1. Our results reveal the remarkable morphological plasticity of H. volcanii cells in response to multiple culture conditions, and should facilitate the use of this species in further studies of archaeal biology.

中文翻译：

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改善 Haloferax volcanii 的生长和形态可塑性

一些微生物表现出多形性，在单一培养物中显示出可变的细胞形状，而另一些则通过分化来适应环境条件的变化。多形性古生菌 Haloferax volcanii 在培养中通常形成盘状（“板”）细胞，但也可能以杆状存在，并且可以在软琼脂中发育成活动杆，或在某些生物膜中发育成更长的细丝。在这里，我们报告了通过补充八种微量元素微量营养素，H. volcanii 在半限定培养基和复杂培养基中的生长改善。使用这些补充培养基，在生长的早期对数期清楚地观察到平板细胞瞬时发育成均匀形状的杆；然后将细胞恢复到平板，用于后期对数和固定相。在用高纯水和试剂配制的培养基中，不添加微量元素，在培养物的所有生长阶段都观察到杆状体和其他复杂的细长形态（“多形性杆状体”）；高度拉长的细胞有时在一个或更少的两极显示出大量的小管，以及不寻常的锥形和高度弯曲的形式。观察到极性小管通过最初的中间细胞变窄或管状形成，导致哑铃状形状，然后向一端细胞分裂。均匀早期对数期杆状体以及多形性杆状体和小管的形成取决于微管蛋白样细胞骨架蛋白 CetZ1 的功能。我们的研究结果揭示了 H. volcanii 细胞在多种培养条件下具有显着的形态可塑性，应该有助于该物种在古菌生物学的进一步研究中的应用。