Bacteriologist over regret uplifted (7)
I believe the answer is:
pasteur
'bacteriologist' is the definition.
(I've seen this before)
'over regret uplifted' is the wordplay.
'over' becomes 'past' (both can mean finished).
'regret' becomes 'rue' (to rue something is to regret it).
'uplifted' says the letters should be written backwards.
'rue' written backwards gives 'eur'.
'past'+'eur'='PASTEUR'
(Other definitions for pasteur that I've seen before include "Louis -, nineteenth century French chemist" , "Louis --, French bacteriologist" , "He developed the partial sterilization of milk" , "Louis --, French chemist/bacteriologist" , "French chemist and biologist (1822-1895)" .)