Mass spectrometry monitoring of rhamnolipids from a growing culture of Pseudomonas aeruginosa strain 57RP

Two rapid and simple methods for the characterisation and quantification of rhamnolipids produced by a growing culture of the Pseudomonas aeruginosa s train 57RP were developed. Two rhamnolipids were purified and their respons e factors determined. The various rhamnolipids produced were then measured using liquid chromatography/mass spectrometry. The culture supernatants wer e injected directly, without prior purification, in a HPLC equipped with a C-18 reverse-phase column. The complete profile of rhamnolipid congeners pr oduced during a 2 week cultivation period was monitored. In order to shorte n the analysis time, another method was developed which did not require chr omatographic separation of the rhamnolipids prior to their detection. Quant ification of rhamnolipids using the direct infusion method gave results ver y similar to those obtained with HPLC separation. These two methods were ve ry well correlated with the standard colorimetric orcinol method. The rhamn olipid profiles obtained show that the various rhamnolipid congeners are se creted simultaneously, and that their relative proportion remained unchange d throughout the cultivation period. (C) 2000 Elsevier Science B.V. All rig hts reserved.