Viral footprints in the cold biosphere revealed by genomic analysis of High Arctic Nostoc from historical and modern samples

In 1875, the British Arctic Expedition to the North Pole, led by Sir George Strong Nares, explored and mapped for the first time the northern coastline of Canada. The surgeon and naturalist on board made many collections of plants and other biological materials, including algae and cyanobacteria. One of the biological specimens deposited by the Nares expedition in the herbarium of the Natural History Museum of London (NHM) was of Nostoc commune Vaucher. This foliose cyanobacterial species is widely distributed throughout the world, and is one of the dominant cyanobacteria in Arctic and Antarctic lakes, ponds, streams and moist soils. We removed a small section of dried thallus from the NHM herbarium and sequenced its genomic DNA. For comparison, we also sequenced the genome of one Nostoc sp. sampled at Ward Hunt Island, Canadian High Arctic in 2015 and also a Nostocales sample from a New Zealand temperate lake.