School of Biotechnology and Biomolecular Sciences, UNSW Sydney, Sydney, New South Wales, 2052, Australia.
Present address: Department of Molecular Sciences, Macquarie University, Sydney, New South Wales, 2109, Australia.
Microbiome. 2021 Nov 26;9(1):231. doi: 10.1186/s40168-021-01173-z.
In Antarctica, summer sunlight enables phototrophic microorganisms to drive primary production, thereby "feeding" ecosystems to enable their persistence through the long, dark winter months. In Ace Lake, a stratified marine-derived system in the Vestfold Hills of East Antarctica, a Chlorobium species of green sulphur bacteria (GSB) is the dominant phototroph, although its seasonal abundance changes more than 100-fold. Here, we analysed 413 Gb of Antarctic metagenome data including 59 Chlorobium metagenome-assembled genomes (MAGs) from Ace Lake and nearby stratified marine basins to determine how genome variation and population structure across a 7-year period impacted ecosystem function.
A single species, Candidatus Chlorobium antarcticum (most similar to Chlorobium phaeovibrioides DSM265) prevails in all three aquatic systems and harbours very little genomic variation (≥ 99% average nucleotide identity). A notable feature of variation that did exist related to the genomic capacity to biosynthesize cobalamin. The abundance of phylotypes with this capacity changed seasonally ~ 2-fold, consistent with the population balancing the value of a bolstered photosynthetic capacity in summer against an energetic cost in winter. The very high GSB concentration (> 10 cells ml in Ace Lake) and seasonal cycle of cell lysis likely make Ca. Chlorobium antarcticum a major provider of cobalamin to the food web. Analysis of Ca. Chlorobium antarcticum viruses revealed the species to be infected by generalist (rather than specialist) viruses with a broad host range (e.g., infecting Gammaproteobacteria) that were present in diverse Antarctic lakes. The marked seasonal decrease in Ca. Chlorobium antarcticum abundance may restrict specialist viruses from establishing effective lifecycles, whereas generalist viruses may augment their proliferation using other hosts.
The factors shaping Antarctic microbial communities are gradually being defined. In addition to the cold, the annual variation in sunlight hours dictates which phototrophic species can grow and the extent to which they contribute to ecosystem processes. The Chlorobium population studied was inferred to provide cobalamin, in addition to carbon, nitrogen, hydrogen, and sulphur cycling, as critical ecosystem services. The specific Antarctic environmental factors and major ecosystem benefits afforded by this GSB likely explain why such a coherent population structure has developed in this Chlorobium species. Video abstract.
在南极洲，夏季阳光使光养微生物能够进行初级生产，从而“喂养”生态系统，使它们能够在漫长的黑暗冬季中得以维持。在 Vestfold Hills 的 Ace 湖中，一种绿硫细菌（GSB）的Chlorobium 物种是主要的光养生物，尽管其季节性丰度变化超过 100 倍。在这里，我们分析了包括来自 Ace 湖和附近分层海洋盆地的 59 个 Chlorobium 宏基因组组装基因组（MAG）在内的 413 Gb 南极宏基因组数据，以确定在 7 年期间，基因组变异和种群结构如何影响生态系统功能。
在所有三个水生系统中，单一物种 Candidatus Chlorobium antarcticum（与 Chlorobium phaeovibrioides DSM265 最为相似）占主导地位，其基因组变异很小（≥99%的平均核苷酸同一性）。存在的一个显著变异特征与生物合成钴胺素的基因组能力有关。具有这种能力的类群的丰度季节性变化约为 2 倍，这与种群在夏季平衡增强的光合作用能力与冬季的能量成本相一致。高浓度的 GSB（Ace 湖中>10 个细胞/ml）和细胞裂解的季节性循环可能使 Ca. Chlorobium antarcticum 成为食物网中钴胺素的主要提供者。对 Ca. Chlorobium antarcticum 病毒的分析表明，该物种被具有广泛宿主范围（例如感染 Gamma-proteobacteria）的普通（而非专门）病毒感染，这些病毒存在于各种南极湖泊中。Ca. Chlorobium antarcticum 丰度的明显季节性下降可能限制了专门病毒建立有效的生命周期，而普通病毒可能会利用其他宿主来增强它们的增殖。
塑造南极微生物群落的因素正在逐渐被定义。除了寒冷之外，光照时间的年度变化决定了哪些光养生物可以生长，以及它们对生态系统过程的贡献程度。所研究的 Chlorobium 种群被推断为提供碳、氮、氢和硫循环以及关键的生态系统服务之外的钴胺素。这种 GSB 可能解释了为什么这种 Chlorobium 物种形成了如此一致的种群结构，这归因于特定的南极环境因素和主要的生态系统效益。视频摘要。
