The influence of rhamnolipids on aliphatic fractions of diesel oil biodegradation by microorganism combinations.

Twelve different bacteria-yeast combinations were tested for determination of their ability to biodegrade diesel oil. The cell surface properties of the bacterial and yeast strains were correlated with the type of carbon source used in the experiments. The highest biodegradation of diesel oil after 7 days was obtained for the following combinations: Aeromonas hydrophila MR4-Yarrowia lipolytica EH 56 (87 %) and Xantomonas maltophila MRP7-Candida maltosa EH15 (90 %). Degradation performances of 10 of 12 combinations were enhanced by the presence of rhamnolipids. The highest increases were observed for A. hydrophila MR4-C. maltosa EH15 (from 34 to 67 %), A. hydrophila MR4-C. maltosa EH60 (from 47 to 76 %) and for Pseudomonas stutzeri MR7-C. maltosa EH60 (from 29 to 79 %). The addition of rhamnolipids to the system reduces the removal time of diesel oil from the contaminated water and changes the microbial adhesion to hydrocarbons. Modification of the cell surface of the tested strain during biodegradation is a very important factor determining the removal of hydrophobic compounds.