Nano-sized archaeota, with their small genomes and limited metabolic capabilities, are known to associate with other microbes, thereby compensating for their own auxotrophies. These diminutive and yet ubiquitous organisms thrive in hypersaline habitats that they share with haloarchaea. Here, we reveal the genetic and physiological nature of a nanohaloarchaeon–haloarchaeon association, with both microbes obtained from a solar saltern and reproducibly cultivated together in vitro. The nanohaloarchaeon Candidatus Nanohalobium constans LC1Nh is an aerotolerant, sugar-fermenting anaerobe, lacking key anabolic machinery and respiratory complexes. The nanohaloarchaeon cells are found physically connected to the chitinolytic haloarchaeon Halomicrobium sp. LC1Hm. Our experiments revealed that this haloarchaeon can hydrolyze chitin outside the cell (to produce the monosaccharide N-acetylglucosamine), using this beta-glucan to obtain carbon and energy for growth. However, LC1Hm could not metabolize either glycogen or starch (both alpha-glucans) or other polysaccharides tested. Remarkably, the nanohaloarchaeon’s ability to hydrolyze glycogen and starch to glucose enabled growth of Halomicrobium sp. LC1Hm in the absence of a chitin. These findings indicated that the nanohaloarchaeon–haloarchaeon association is both mutualistic and symbiotic; in this case, each microbe relies on its partner’s ability to degrade different polysaccharides. This suggests, in turn, that other nano-sized archaeota may also be beneficial for their hosts. Given that availability of carbon substrates can vary both spatially and temporarily, the susceptibility of Halomicrobium to colonization by Ca. Nanohalobium can be interpreted as a strategy to maximize the long-term fitness of the host.

纳米尺度的古细菌具有小的基因组和有限的代谢能力，已知会与其他微生物结合，从而补偿其自身的营养缺陷。这些微小但无处不在的生物在与盐生古生物共有的高盐生境中繁衍。在这里，我们揭示了纳米卤代古细菌-卤代古细菌协会的遗传和生理特性，两种微生物均来自太阳盐分离器，并在体外可复制地共同培养。该nanohaloarchaeon暂定Nanohalobium CONSTANS LC1Nh是耐氧，糖发酵厌氧菌，缺乏关键蛋白同化机械和呼吸配合。发现纳米卤代古细菌细胞与几丁质分解卤代古细菌Halomicrobium物理连接sp。LC1Hm。我们的实验表明，这种卤代古细菌可以利用细胞中的几丁质水解甲壳素（产生单糖N-乙酰氨基葡糖），并使用这种β-葡聚糖来获得生长所需的碳和能量。然而，LC1Hm不能代谢糖原或淀粉（均为α-葡聚糖）或其他测试的多糖。值得注意的是，纳米卤代古细菌将糖原和淀粉水解为葡萄糖的能力使得卤代微生物得以生长sp。没有甲壳质时的LC1Hm。这些发现表明，纳米卤代古细菌与卤代古细菌之间的联系是相互的和共生的。在这种情况下，每种微生物都依赖于其伴侣降解不同多糖的能力。反过来，这表明其他纳米大小的古细菌也可能对其宿主有益。鉴于碳底物的可用性在空间和暂时上都可能发生变化，因此，卤化微生物对Ca定植的敏感性。纳米ha可以解释为最大化宿主长期适应性的策略。