Manufacture bacteria, mutating with frequency (9)
I believe the answer is:
fabricate
'manufacture' is the definition.
(I know that manufacture can be written as fabricate)
'bacteria mutating with frequency' is the wordplay.
'mutating with' indicates an anagram (I've seen 'mutate' mean this).
'frequency' becomes 'f' (abbreviation e.g. FM radio).
'bacteria' anagrammed with 'f' can make 'FABRICATE'.
(Other definitions for fabricate that I've seen before include "Invent, make up" , "Tell lies" , "forge" , "Invent or manufacture a story" , "Make up; manufacture" .)