Abstract
Lake Chaohu, one of the five largest freshwater lakes in China, has been suffering from severe cyanobacterial blooms in the summer for many years. Cyanophages, the viruses that specifically infect cyanobacteria, play a key role in modulating cyanobacterial population, and thus regulate the emergence and decline of cyanobacterial blooms. Here we report a long-tailed cyanophage isolated from Lake Chaohu, termed Mic1, which specifically infects the cyanobacterium Microcystis aeruginosa. Mic1 has an icosahedral head of 88 nm in diameter and a long flexible tail of 400 nm. It possesses a circular genome of 92,627 bp, which contains 98 putative open reading frames. Genome sequence analysis enabled us to define a novel terminase large subunit that consists of two types of intein, indicating that the genome packaging of Mic1 is under fine control via posttranslational maturation of the terminase. Moreover, phylogenetic analysis suggested Mic1 and mitochondria share a common evolutionary origin of DNA polymerase γ gene. All together, these findings provided a start-point for investigating the co-evolution of cyanophages and its cyanobacterial hosts.
Highlights
Cyanobacteria, which have existed on the earth for more than 3.5 billion years, are widely distributed in aquatic environments (Zhang and Gui, 2018)
After being concentrated to about 100-fold by ultrafiltration, the water samples were applied to infect 11 cyanobacterial strains isolated from Lake Chaohu, the lytic cyanophages infecting previously named Microcystis wesenbergii FACHB 1339 were further isolated by the serial dilution method (Yoshida et al, 2006)
Lake Chaohu has been severely polluted in recent years, owing to a large amount of industrial waste water and domestic sewage flowing from the rivers of Shiwuli, Nanfei, Shuangqiao and Xiapai, which are major rivers to the lake
Summary
Cyanobacteria, which have existed on the earth for more than 3.5 billion years, are widely distributed in aquatic environments (Zhang and Gui, 2018). As a group of photosynthetic bacteria, cyanobacteria provide the source of primary production of oxygen, nitrogen, and carbon, and act as a model organism for studying the coordination of carbon and nitrogen metabolisms (Jiang et al, 2018). Beyond contributing to biogeochemical cycle, blooms yield toxicity and hypoxia of waterbodies, which was first investigated in the Lake Alexandrina of Australia in 1878 (Francis, 1878). Blooms are increasing in frequency, magnitude, and duration in recent years, and cause the death of fish and risk to human diet (Paerl et al, 2001; Huisman et al, 2018). It becomes imperative to devise an effective strategy to mitigate and control the water blooms
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