The Collaborative International Dictionary of English v.0.48:

myxobacterium \myxobacterium\ n.; pl. myxobacteria.
   A type of bacteria that form colonies in self-produced slime;
   they inhabit moist soils or decaying plant matter or animal
   waste.

   Syn: myxobacterium, myxobacter, gliding bacteria, slime
        bacteria.
        [WordNet 1.5]

WordNet (r) 3.0 (2006):

myxobacterium
    n 1: bacteria that form colonies in self-produced slime; inhabit
         moist soils or decaying plant matter or animal waste [syn:
         myxobacteria, myxobacterium, myxobacter, gliding
         bacteria, slime bacteria]