Department of Chemical Science and Engineering, Tokyo Institute of Technology.
Earth-Life Science Institute, Tokyo Institute of Technology.
Microbes Environ. 2021;36(2). doi: 10.1264/jsme2.ME20138.
Cyanobacteria thrive in diverse environments. However, questions remain about possible growth limitations in ancient environmental conditions. As a single genus, the Thermosynechococcus are cosmopolitan and live in chemically diverse habitats. To understand the genetic basis for this, we compared the protein coding component of Thermosynechococcus genomes. Supplementing the known genetic diversity of Thermosynechococcus, we report draft metagenome-assembled genomes of two Thermosynechococcus recovered from ferrous carbonate hot springs in Japan. We find that as a genus, Thermosynechococcus is genomically conserved, having a small pan-genome with few accessory genes per individual strain as well as few genes that are unique to the genus. Furthermore, by comparing orthologous protein groups, including an analysis of genes encoding proteins with an iron related function (uptake, storage or utilization), no clear differences in genetic content, or adaptive mechanisms could be detected between genus members, despite the range of environments they inhabit. Overall, our results highlight a seemingly innate ability for Thermosynechococcus to inhabit diverse habitats without having undergone substantial genomic adaptation to accommodate this. The finding of Thermosynechococcus in both hot and high iron environments without adaptation recognizable from the perspective of the proteome has implications for understanding the basis of thermophily within this clade, and also for understanding the possible genetic basis for high iron tolerance in cyanobacteria on early Earth. The conserved core genome may be indicative of an allopatric lifestyle-or reduced genetic complexity of hot spring habitats relative to other environments.
蓝藻在各种环境中茁壮成长。然而，对于它们在古代环境条件下可能存在的生长限制问题，仍存在疑问。作为一个单一的属，聚球藻属是世界性的，生活在化学多样性的栖息地。为了了解这一现象的遗传基础，我们比较了聚球藻属基因组的蛋白质编码成分。除了已知的聚球藻属的遗传多样性外，我们还报告了从日本亚铁碳酸盐温泉中回收的两个聚球藻属的草案宏基因组组装基因组。我们发现，作为一个属，聚球藻属在基因组上是保守的，具有一个小的泛基因组，每个菌株的辅助基因很少，而且只有少数基因是属特有的。此外，通过比较直系同源蛋白组，包括对与铁相关功能（摄取、储存或利用）相关的基因编码蛋白的分析，尽管它们栖息的环境范围不同，但在属成员之间没有发现遗传内容或适应机制的明显差异。总的来说，我们的研究结果突出了聚球藻属似乎具有内在的能力，能够在没有经历大量基因组适应以适应这种情况的情况下栖息于多种生境。在没有从蛋白质组角度识别出适应的情况下，在高温和高铁环境中发现聚球藻属，这对理解该进化枝中嗜热的基础以及理解早期地球上蓝藻对高铁耐受性的可能遗传基础具有重要意义。保守的核心基因组可能表明聚球藻属的生活方式是异地的，或者温泉生境的遗传复杂性相对于其他环境较低。
