Belcher's virus of choice is the M13 bacteriophage, a cigar-shaped virus that replicates in bacteria. Although it's not the only virus that can be used for nanoengineering, Belcher says it works well because its genetic material is easy to manipulate.
Source: https://www.wired.com/story/the-next-generation-of-batteries-could-be-built-by-viruses
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