Merry Youle from From the Small Things Considered Blog points readers to an article by Hans-Dieter Görtz on the fascinating relationships between ciliates and bacteria.
"Organisms such as ciliates that dine daily on bacteria run the risk of getting an infection. Indeed, ciliates—large, complex cells—are host in nature to gazillion different bacteria that they acquire primarily through phagocytosis at their "mouth." Resident bacteria are generally termed symbionts even though only a few of them have been studied enough to reveal the nature of their intimate relationship. The stories of those chosen few are recounted in an engrossing review by Hans-Dieter Görtz"