Feeding behavior of organisms that prey on microorganisms
Use "-vore" and "-vorous" suffix [L. -vorus devouring, eating (cf. vorāre to devour].

For example: bacteriovores, algaevores, and planktivores.



Note: "Microorganism" is an unfortunate, albeit popular (viz. "microbiology") term. How small is "micro"? So small that one needs a microscope to see it? And what kind of microscope: "light" or "electron"? i would drop the term "microorganism" altogether. One can use "bacteria, "archaea," "chromists," "protists," . . .