Institute of Evolution, MTA Centre for Ecological Research, Budapest, Hungary.
ASA Program, International Institute for Applied Systems Analysis (IIASA), Laxenburg, Austria.
Sci Rep. 2023 Jan 17;13(1):907. doi: 10.1038/s41598-023-27421-w.
Syntrophic cooperation among prokaryotes is ubiquitous and diverse. It relies on unilateral or mutual aid that may be both catalytic and metabolic in nature. Hypotheses of eukaryotic origins claim that mitochondrial endosymbiosis emerged from mutually beneficial syntrophy of archaeal and bacterial partners. However, there are no other examples of prokaryotic syntrophy leading to endosymbiosis. One potential reason is that when externalized products become public goods, they incite social conflict due to selfish mutants that may undermine any mutualistic interactions. To rigorously evaluate these arguments, here we construct a general mathematical framework of the ecology and evolution of different types of syntrophic partnerships. We do so both in a general microbial and in a eukaryogenetic context. Studying the case where partners cross-feed on each other's self-inhibiting waste, we show that cooperative partnerships will eventually dominate over selfish mutants. By contrast, systems where producers actively secrete enzymes that cross-facilitate their partners' resource consumption are not robust against cheaters over evolutionary time. We conclude that cross-facilitation is unlikely to provide an adequate syntrophic origin for endosymbiosis, but that cross-feeding mutualisms may indeed have played that role.
原核生物之间的共生合作是普遍存在且多样化的。它依赖于单边或互助，可能具有催化和代谢性质。真核生物起源的假说认为，线粒体的内共生是由古细菌和细菌伙伴之间互利共生的共生关系产生的。然而，没有其他例子表明原核共生会导致内共生。一个潜在的原因是，当外化产物成为公共物品时，由于自私的突变体可能破坏任何互利相互作用，它们会引发社会冲突。为了严格评估这些论点，我们在这里构建了一个不同类型共生伙伴关系的生态学和进化的一般数学框架。我们在一般微生物和真核生物发生的背景下进行了这样的研究。通过研究伙伴之间相互喂食彼此自我抑制的废物的情况，我们表明合作伙伴关系最终将战胜自私的突变体。相比之下，在生产者主动分泌酶来促进其合作伙伴资源消耗的系统中，在进化时间上，对于欺骗者来说，系统并不稳健。我们的结论是，交叉促进不太可能为内共生提供一个充分的共生起源，但交叉喂养的互利共生关系可能确实起到了这样的作用。
