Many microbes produce stress-resistant spores to survive unfavorable conditions [1, 2, 3, 4] and enhance dispersal [1, 5]. Cooperative behavior is integral to the process of spore formation in some species [3, 6], but the degree to which germination of spore populations involves social interactions remains little explored. Myxococcus xanthus is a predatory soil bacterium that upon starvation forms spore-filled multicellular fruiting bodies that often harbor substantial diversity of endemic origin [7, 8]. Here we demonstrate that germination of M. xanthus spores formed during fruiting-body development is a social process involving at least two functionally distinct social molecules. Using pairs of natural isolates each derived from a single fruiting body that emerged on soil, we first show that spore germination exhibits positive density dependence due to a secreted “public-good” germination factor. Further, we find that a germination defect of one strain under saline stress in pure culture is complemented by addition of another strain that germinates well in saline environments and mediates cheating by the defective strain. Glycine betaine, an osmo-protectant utilized in all domains of life, is found to mediate saline-specific density dependence and cheating. Density dependence in non-saline conditions is mediated by a distinct factor, revealing socially complex spore germination involving multiple social molecules.

许多微生物产生抗压孢子以在不利条件下存活 [1, 2, 3, 4] 并促进传播 [1, 5]。合作行为是某些物种孢子形成过程中不可或缺的一部分 [3, 6]，但孢子种群的萌发涉及社会相互作用的程度仍然很少被探索。Myxococcus xanthus是一种掠食性土壤细菌，在饥饿时会形成充满孢子的多细胞子实体，这些子实体通常具有大量的地方性起源多样性 [7, 8]。在这里我们证明M. xanthus 的萌发在子实体发育过程中形成的孢子是一个社会过程，涉及至少两个功能不同的社会分子。使用来自土壤上出现的单个子实体的成对天然分离物，我们首先表明，由于分泌的“公共物品”萌发因子，孢子萌发表现出正密度依赖性。此外，我们发现纯培养中盐胁迫下一个菌株的萌发缺陷通过添加另一种在盐水环境中发芽良好并介导缺陷菌株欺骗的菌株得到补充。甘氨酸甜菜碱是一种在生活的所有领域中使用的渗透保护剂，被发现介导盐水特定的密度依赖性和作弊。非盐度条件下的密度依赖性是由一个独特的因素介导的，