HPLC separation of crude extracts obtained from R. rubrum Fed-batch culture supernatants at OD = 50. Chemical structures and molecular weights (Mw) of identified AHLs are indicated (for a list of measured m/z values see supporting material). Single peaks were isolated by semi-preparative HPLC and applied to A. tumefaciens NTL4 on agar plates. The inserts show the biological activity as blue colour reaction. Volume of HPLC eluate loaded onto agar containing A. tumefaciens is indicated in μL.