Population structure of an Antarctic aquatic cyanobacterium

• Published in: Microbiome
• Main Authors: Pratibha Panwar, Timothy J. Williams, Michelle A. Allen, Ricardo Cavicchioli
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2022
• Subjects: Antarctic microbiology; Cyanobacteria; Synechococcus; Regnicoccus; Nit1C; AsnB; Microbial ecology; QR100-130; Antarctic; East Antarctica; Vestfold Hills; Vestfold; Ace Lake; Antarc*; Antarctica
• Online Access: https://doi.org/10.1186/s40168-022-01404-x; https://doaj.org/article/2091b313726d461d8ce2ff9860cc9a7c

Abstract Background Ace Lake is a marine-derived, stratified lake in the Vestfold Hills of East Antarctica with an upper oxic and lower anoxic zone. Cyanobacteria are known to reside throughout the water column. A Synechococcus-like species becomes the most abundant member in the upper sunlit waters during summer while persisting annually even in the absence of sunlight and at depth in the anoxic zone. Here, we analysed ~ 300 Gb of Ace Lake metagenome data including 59 Synechococcus-like metagenome-assembled genomes (MAGs) to determine depth-related variation in cyanobacterial population structure. Metagenome data were also analysed to investigate viruses associated with this cyanobacterium and the host’s capacity to defend against or evade viruses. Results A single Synechococcus-like species was found to exist in Ace Lake, Candidatus Regnicoccus frigidus sp. nov., consisting of one phylotype more abundant in the oxic zone and a second phylotype prevalent in the oxic-anoxic interface and surrounding depths. An important aspect of genomic variation pertained to nitrogen utilisation, with the capacity to perform cyanide assimilation and asparagine synthesis reflecting the depth distribution of available sources of nitrogen. Both specialist (host specific) and generalist (broad host range) viruses were identified with a predicted ability to infect Ca. Regnicoccus frigidus. Host-virus interactions were characterised by a depth-dependent distribution of virus type (e.g. highest abundance of specialist viruses in the oxic zone) and host phylotype capacity to defend against (e.g. restriction-modification, retron and BREX systems) and evade viruses (cell surface proteins and cell wall biosynthesis and modification enzymes). Conclusion In Ace Lake, specific environmental factors such as the seasonal availability of sunlight affects microbial abundances and the associated processes that the microbial community performs. Here, we find that the population structure for Ca. Regnicoccus frigidus has evolved differently to the ...