A variety of recti found in bottom microbe (9)
I believe the answer is:
bacterium
'microbe' is the definition.
(thesaurus)
'a variety of recti found in bottom' is the wordplay.
'a variety of' indicates anagramming the letters.
'found in' means one lot of letters goes inside another.
'bottom' becomes 'baum' (I can't justify this - if you can you should believe this answer much more).
'recti' anagrammed gives 'cteri'.
'cteri' put into 'baum' is 'BACTERIUM'.
Can you help me to learn more?
(Other definitions for bacterium that I've seen before include "Micro-organism that can cause disease" , "health risk?" , "Fundamental" , "germ?" .)