Remarkably coherent population structure for a dominant Antarctic Chlorobium species

• Published in: Microbiome
• Main Authors: Panwar, P, Allen, MA, Williams, TJ, Haque, S, Brazendale, S, Hancock, A, Paez-Espino, D, Cavicchioli, R
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: BioMed Central 2021
• Subjects: Antarctic microbiology; Chlorobi; Ecotype; Generalist virus; Green sulphur bacteria; Host-virus interactions; Meromictic lake; Metagenome-assembled genomes; Microbial food web; Phylotype; Population structure; Vitamin B12; Antarctic; East Antarctica; Vestfold Hills; Vestfold; Ace Lake; Antarc*; Antarctica
• Online Access: https://eprints.utas.edu.au/47166/

Background: 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.Results: 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 (> 108 cells ml-1 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.Conclusion: The factors shaping Antarctic microbial communities are gradually being defined. In addition to the cold, the annual variation in ...