This term for 2 dissimilar organisms living together in mutualism comes from the Greek for "with" & "life"
The term symbiosis (from the Greek:  syn "with"; and  
biosis "living")... [DOC] [TLE] symbiosis facts, information, pictures | Encyclopedia.com articles ... [PAR] Symbiosis is a biological relationship in which two species live in close .... of 
inorganic nutrients, especially phosphorus, that come from the fungus.