Below is an image of Thiomargarita magnifica, the world's largest bacterium that scientists just discovered in the French Caribbean hanging out on underwater on decaying leaves from a mangrove tree. The size and shape of a human eyelash, you can see it without a microscope. (The illustration above shows the lil' creature beside a dime.) From the BBC News:
"These bacteria are about 5,000 times larger than most bacteria. And to put things into perspective, it is the equivalent for us humans to encounter another human who would be as tall as Mount Everest," said Jean-Marie Volland from the Joint Genome Institute at the Lawrence Berkeley National Laboratory, in the US[…]
[In the bacterium's] DNA, there are clues to the drivers of the organism's great size, [LBNL scientist Dr Tanja Woyke] added. Some genes associated with elongation seem to be duplicated and some genes ordinarily involved in division appear to be missing.
Learn more: "Giant Bacteria Found in Guadeloupe Mangroves Challenge Traditional Concepts" (Berkeley Lab)