Cyanobacteria thrive in very diverse environments. In Earth history however, delayed oxygenation has raised questions of growth limitation in ancient environmental conditions. As a single genus, the Thermosynechococcus are known to be 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 and only 18 protein clusters appearing in all Thermosynechococcus but not in any other cyanobacteria in our analysis. 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 protein coding genes has implications for understanding the basis of thermophily within this clade, and also suggests that ferrous iron in ancient oceans may not have inhibited the proliferation of Cyanobacteria on Earth. The conserved core genome may be indicative of an allopatric lifestyle - or reduced genetic complexity of hot spring habitats relative to other environments.

中文翻译：

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嗜热球菌属：广泛的环境分布，但高度保守的基因组核心

蓝细菌在非常多样的环境中壮成长。然而，在地球历史上，延迟的氧合作用提出了在古代环境条件下生长受限的问题。嗜热嗜热球菌作为一个属，是世界性的，生活在化学上多样化的栖息地中。为了了解其遗传基础，我们比较了嗜热球菌基因组的蛋白质编码成分。作为对嗜热嗜热球菌的已知遗传多样性的补充，我们报告了从日本碳酸亚铁温泉中回收的两个嗜热嗜热球菌的基因组组装基因组草案。我们发现，作为一个属，嗜热嗜热球菌是基因组保守的，具有一个小的全基因组，每个菌株的辅助基因很少，在我们的分析中，所有嗜热嗜热球菌只有18个蛋白质簇出现，而没有其他蓝藻出现。此外，通过比较直系同源蛋白质组，包括对编码具有铁相关功能（摄取，储存或利用）的蛋白质的基因进行分析，尽管环境范围很广，但在属成员之间无法检测到遗传含量或适应机制的明显差异他们居住。总的来说，我们的结果突出了嗜热嗜热球菌似乎具有先天的能力，可以在不进行大量基因组适应而适应各种栖息地的情况下栖息。在高温和高铁环境中发现嗜热嗜热球菌均无法从蛋白质编码基因的角度识别适应性变化，这有助于理解该进化枝中嗜热菌的基础，也暗示古代海洋中的亚铁可能未抑制蓝藻细菌的增殖。在地球上。