School of Biotechnology and Biomolecular Sciences and Centre for Marine Bio-Innovation, University of New South Wales, Sydney, New South Wales 2052, Australia.
Proc Natl Acad Sci U S A. 2012 Jul 3;109(27):E1878-87. doi: 10.1073/pnas.1203287109. Epub 2012 Jun 13.
Microorganisms often form symbiotic relationships with eukaryotes, and the complexity of these relationships can range from those with one single dominant symbiont to associations with hundreds of symbiont species. Microbial symbionts occupying equivalent niches in different eukaryotic hosts may share functional aspects, and convergent genome evolution has been reported for simple symbiont systems in insects. However, for complex symbiont communities, it is largely unknown how prevalent functional equivalence is and whether equivalent functions are conducted by evolutionarily convergent mechanisms. Sponges represent an evolutionarily divergent group of species with common physiological and ecological traits. They also host complex communities of microbial symbionts and thus are the ideal model to test whether functional equivalence and evolutionary convergence exist in complex symbiont communities across phylogenetically divergent hosts. Here we use a sampling design to determine the phylogenetic and functional profiles of microbial communities associated with six sponge species. We identify common functions in the six microbiomes, demonstrating the existence of functional equivalence. These core functions are consistent with our current understanding of the biological and ecological roles of sponge-associated microorganisms and also provide insight into symbiont functions. Importantly, core functions also are provided in each sponge species by analogous enzymes and biosynthetic pathways. Moreover, the abundance of elements involved in horizontal gene transfer suggests their key roles in the genomic evolution of symbionts. Our data thus demonstrate evolutionary convergence in complex symbiont communities and reveal the details and mechanisms that underpin the process.
微生物通常与真核生物形成共生关系，这些关系的复杂性范围从单一主导共生体到与数百种共生体物种的关联。在不同真核宿主中占据等效生态位的微生物共生体可能具有功能方面的相似性，昆虫中简单共生体系统的趋同进化基因组已被报道。然而，对于复杂的共生体群落，功能等效性的普遍性以及等效功能是否通过进化趋同机制来执行在很大程度上是未知的。海绵代表了一组具有共同生理和生态特征的进化分歧物种。它们还容纳了复杂的微生物共生体群落，因此是测试功能等效性和进化趋同是否存在于进化分歧宿主的复杂共生体群落中的理想模型。在这里，我们使用采样设计来确定与六种海绵物种相关的微生物群落的系统发育和功能特征。我们确定了六个微生物组中的共同功能，证明了功能等效性的存在。这些核心功能与我们目前对海绵相关微生物的生物学和生态作用的理解一致，也为共生体功能提供了新的见解。重要的是，核心功能也由类似的酶和生物合成途径在每种海绵物种中提供。此外，涉及水平基因转移的元素的丰度表明它们在共生体基因组进化中的关键作用。因此，我们的数据证明了复杂共生体群落中的进化趋同，并揭示了支持该过程的细节和机制。
