Remarkably coherent population structure for a dominant Antarctic Chlorobium species

Area of Science:

• Microbiology
• Antarctic Science
• Genomics

Background:

• Antarctic ecosystems rely on phototrophic microorganisms for primary production.
• Ace Lake, a marine-derived Antarctic system, hosts a dominant Chlorobium species (GSB) with significant seasonal abundance fluctuations.
• Understanding GSB genome variation and population structure is key to comprehending Antarctic ecosystem function.

Purpose of the Study:

• Analyze metagenomic data to investigate genome variation and population structure of Antarctic Chlorobium species.
• Determine the impact of genome variation on ecosystem function over a 7-year period.
• Assess the role of GSB in cobalamin biosynthesis and its seasonal variation.

Main Methods:

• Analysis of 413 Gb of Antarctic metagenome data.
• Assembly of 59 Chlorobium metagenome-assembled genomes (MAGs).
• Comparative genomic analysis to identify variations, particularly in cobalamin biosynthesis pathways.

Main Results:

• A single species, Candidatus Chlorobium antarcticum, dominates, exhibiting high genomic similarity (≥99% ANI).
• Genomic variation in cobalamin biosynthesis capacity showed a ~2-fold seasonal change in phylotype abundance.
• Ca. Chlorobium antarcticum is infected by generalist viruses, with its seasonal decline potentially favoring generalist over specialist viruses.

Conclusions:

• Ca. Chlorobium antarcticum plays a crucial role in cobalamin provision to the Antarctic food web.
• Seasonal GSB population dynamics and lysis contribute significantly to nutrient cycling and ecosystem services.
• High GSB concentration and specific Antarctic environmental factors likely drive the coherent population structure observed in this species.