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Swimming with Viruses In Pavilion Lake

Posted on July 6th, 2010 by Danielle Winget

Transmission electron micrograph of viruses and bacteria. A, b, and c depict myoviruses, podoviruses, and siphoviruses respectively. Courtesy of Suttle, 2005.

Viruses are Earth’s smallest inhabitants, but they are also her most abundant. Scientists estimate that the Earth houses about 1 x 10^30 viruses compared with just 6 x 10^9 (six billion) humans. A typical teaspoon-full of seawater (or Pavilion Lake water) contains between 10,000 and 100,000 viruses! If you all lined up all the viruses on Earth end to end, they would stretch for 10 million light years. Fortunately for us, the overwhelming majority of viruses are predators of micro-organisms, like bacteria and single-celled algae, and can not infect humans.

Viruses are tiny packets of nucleic acid wrapped in protein shell. They are reliant upon a host cell for their replication and gene expression and are as diverse structurally and genetically as they are abundant. Viruses vary in size from 20 to 600 nanometers in diameter and display a variety of shapes from thin filaments to round blobs to tiny lunar landing ships. Unique among all other life forms, viral genomes can be composed of single or doubled-stranded DNA or RNA.

The arrows point to viruses. Courtesy of Weinbauer, 2004.

Viral genomes are an incredibly source of genetic diversity. Between 60-90% of viral genes are new to science. In other words, these genes have no similarity to bacterial or eukaryotic genes that we have already investigated. Surprisingly, viruses are an essential part of healthy ecosystems. Every day they infect and kill about 20% of the micro-organsims in the ocean, impacting microbial community structure and function as well as releasing nutrients for surviving bacteria to feast upon. Viruses can also move genes between host cells via the process of transduction, making them agents of genetic evolution.

At Pavilion Lake, we are sampling microbialites (Fig. 2 & 3) and filtering large volumes of water (100 liters) to discover if and how viral diversity varies with depth and microbialite morphology. This year we are also working on new project, MARSLIFE, aimed at detecting nucleic acids in micro-volumes of samples (0.25 grams) while in the field from both microbialites and water samples. This directly mirrors how we might search for life on Mars – by looking for DNA in minute amounts of rock or ice. Because viruses likely evolved on the early Earth, studying the viruses of Pavilion Lake provides insight into what life in ancient microbialites and shallow seas might have been like. In the process, we gain a better understanding of not only our planet, but also what other bizarre and unique organisms the universe might be hiding.

Diver bringing a microbialite collected from a depth of 85ft to the surface of Pavilion Lake.

Jan Finke filtering and concentrating viruses from Pavilion Lake water.