It isn't easy to be a phage. First, what is a phage? A phage is a virus that infects microbial cells, specifically bacterial or archaeal cells. To succeed, a phage must encounter, recognize, and then deliver its chromosome into a particular type of cell. This presumptive invasion is met by the cell's state-of-the-art defenses. Unless it dodges or neutralizes every one, the phage chromosome will be chopped into a nutritious snack for the cell. If the phage survives, it then quickly takes over the cell's metabolic machinery and diverts it to production of more phages, rather than more cells. This requires intimate knowledge of the regulatory systems that this host uses to coordinate its activities. The phage skillfully manipulates these activities to provide a steady supply of the energy and materials needed to support phage replication. Under phage supervision, production of phage components proceeds at top speed, with all parts produced when needed and in the quantities required. As the pieces come off the assembly line, they assemble themselves into sophisticated transport packages, each carrying a phage chromosome and capable of delivering it into a new host cell. When a new crop of progeny is ready – perhaps 25, 100, or more of them – the phage ruptures the cell to free them all and send them out into the world in quest of hosts of their own.

These events comprise what is known as standard lytic replication. However, many phages have the option to follow a different script. When they arrive in a host, they can opt to delay immediate hostile takeover and to instead form a coalition with the host. In this case, the phage inserts its chromosome into that of the host. Now, as the host grows and divides, the combined chromosome is replicated and inherited by both daughter cells. This can continue for many generations, with the phage paying rent in the form of some useful services. However, the phage considers that it has signed only a moment-to-moment lease. If the cell encounters life-threatening difficulties, the phage switches to rapid replication. Cell rupture and release of the new phages follows quickly.

Each step of the way presents challenges that test the ingenuity of the phages. In this engaging book, Merry Youle relates some of the tactics used by 21 pheatured phages to outwit their host and successfully maintain their own lineage generation after generation. The text is accompanied by pertinent electron micrographs, tomographic reconstructions, and other structural diagrams; every chapter is enlivened by informative illustrations created by San Diego fine artist Leah Pantéa. The writing focuses on the strategies and underlying principles, with a minimum of jargon. Since some knowledge of molecular biology is required to appreciate the phage wizardry, a primer of the needed basics is provided for those unfamiliar with that subject. Thus, the book is accessible to a wide audience.

Despite being the most abundant life form, the phages – being much smaller than even the microbes they infect – elude our everyday perception. Thinking Like a Phage offers a tour of this unseen dimension of life on Earth. Whether you are an expert or new to the phage world, these vignettes drawn from phage life will intrigue you. Awareness of this vast, creative, yet invisible realm can enrich your appreciation for the living world of which we, as Homo sapiens, are a small part.