Cymbiomics: multipartite interactions and a large-scale approach to pinpointing symbiotic competence of cyanobacteria

蓝藻与真核宿主之间的共生相互作用对地球上生命的进化产生了深远的影响。这是一种蓝藻共生体，最终变成了固碳的叶绿体。然而，在共生中还有另一种突出的蓝藻(蓝藻)。在这里，相互作用围绕着氰基硫化物执行固氮的能力。在一些情况下，这些氰硫磷被紧密地整合到宿主体内，但(尚未)驯化成细胞器。这种现存的相互作用在陆地植物(胚藻门)中得到了最好的描述，但也包括真菌Gesiphon--为数不多的已知自然种群之一在Göttingen附近蓬勃发展。共生蓝藻的大量出现，其中许多仍然能够在没有宿主的情况下生活在一起，这就证明了一个问题，即是什么让它们有资格在第一时间共生。在所有蓝藻共生体中，宿主、蓝藻和相关微生物群落之间存在多方相互作用。因此，我们假设，能够成为蓝藻的蓝藻不仅必须具有与宿主沟通的能力，而且必须具有在多生物生物膜中发挥作用的能力，甚至可能形成多生物生物膜。在这里，我们将探讨两个问题：i)这些蓝藻谱系的共生能力是什么？和ii)蓝藻伙伴的能力是否取决于招募功能正确的微生物组的能力？我们将三管齐下。首先，我们将利用Göttingen的SAG收集，并对从共生和非共生条件下分离的蓝藻菌株进行测序；根据公开获得的基因组，这些数据将与全基因组关联研究和比较基因组学相结合，以准确定位所有能够共生的蓝藻共同的遗传因素。其次，我们将从地虹吸虫和含有氰硫磷的植物Gunnera、Azolla和Anthoceros的多个个体中提取天然存在的蓝硫磷及其微生物群。第三，我们将使用Anthoceros LAB系统对共生能力测序的蓝藻菌株进行表型鉴定，并确定蓝藻接种后花藻-蓝藻共生的微生物群。总之，我们的数据将决定与蓝藻共生能力有关的因素--无论是在天然的还是在栽培的蓝藻中。可能的后续研究将包括在已确定的候选基因中剔除的蓝藻的产生。

The symbiotic interaction between cyanobacteria and eukaryotic hosts had a profound impact on the evolution of life on this planet. It was a cyanobacterial symbiont that eventually was turned into the chloroplasts for carbon-fixation. Yet, there is another prominent type of cyanobacteria in symbiosis (cyanobionts). Here, the interaction revolves around the ability of cyanobionts to perform nitrogen-fixation. In several cases, these cyanobionts are tightly integrated into the host body but have not (yet) been domesticated into an organelle. Such extant interactions are best-described in land plants (Embryophyta), but also the fungus Geosiphon—for which one of the few known natural populations thrives close to Göttingen. The manifold occurrence of symbiotic cyanobacteria, many of which are still capable of living together and apart from their host, warrants the question what made them eligible for a symbiosis in the first place. In all cyanobacterial symbioses, multipartite interactions between the host, the cyanobiont, and an associated microbial community occur. We therefore hypothesize that the cyanobacteria capable to be cyanobionts must have the ability to not only communicate with their hosts but also to function in—and perhaps even shape—a multi-organism biofilm. Here we will explore two questions: i) What manifests the symbiotic competence of these cyanobacterial lineages? and ii) Is the competence of the cyanobacterial partner determined by the capacity to recruit the functionally correct microbiome? We will carry out a three-pronged approach. First, we will leverage the SAG collection in Göttingen and sequence cyanobacterial strains isolated from symbiotic and non-symbiotic conditions; contextualized with publicly available genomes, these data will be combined with genome-wide association studies and comparative genomics to pinpoint genetic factors that is common to all cyanobacteria that are clearly capable of symbiosis. Second, we will sample naturally occurring cyanobionts and their microbiome from multiple individuals of Geosiphon and the cyanobiont-bearing plants Gunnera, Azolla and Anthoceros. Third, we will use the Anthoceros lab system to phenotype the cyanobacterial strains sequenced for symbiotic competency and determine the microbiome of the Anthoceros–cyanobacteria symbiosis after cyanobacterial inoculation. Altogether, our data will determine factors linked to the symbiotic capabilities of the cyanobacteria—both in natural and cultivated cyanobionts. Possible follow-up studies will include generation of cyanobacteria that are knocked out in the identified candidate genes.