By definition, microbes are supposed to be so small they can only be seen with a microscope. But a bacterium living in Caribbean mangroves never got that memo. Its threadlike single cell is visible to the naked eye, growing up to 2 centimeters—as long as a peanut—and 5000 times bigger than many other microbes. What’s more, this giant has a huge genome that’s not free floating inside the cell as in other bacteria, but is instead encased in a membrane, an innovation characteristic of much more com