Supplementary material
Solubilization of phenanthrene in the presence of surfactants
The effective solubilization of phenanthrene is one of the key steps to improve its biodegradation. Indeed, only bioavailable substrate can be degraded by microorganisms. Three surfactants (Tween 80, Brij 30 and rhamnolipids JBR 204) were added to the culture medium in concentrations from 0.05 to 1 g L-1 and their action on phenanthrene (100 mg L-1) was compared in order to define the most effective one. The surfactants were chosen on the basis of their biocompatibility and their ability to solubilize PAHs [12, 14, 17-18]. The suspensions were agitated at 28 0C, 200 rpm for 24 h. In order to get a mathematical expression of the solubilization efficiency of surfactants, the weight solubilization ratio (WSR) was determined. WSR is defined as the weight of organic compound solubilized per unit mass of surfactant added [9]. Figure SM1 shows the correlation of soluble phenanthrene concentrations with those of surfactants. The results indicated on this figure permit to calculate the WSR values of Brij 30, rhamnolipids and Tween 80, expressed as g of phenanthrene/g of surfactant: the WSR values were found equal to 0.0466 g/g, 0.0135 g/g and 0.0137 g/g, respectively. Thus Brij 30 had the highest WSR value and it was shown that, on a mass basis, it dissolves phenanthrene in water better than the two other surfactants. It was therefore used in further biodegradation experiments.
Figure SM1.Determination of weight solubilization ratio (WSR) of surfactants. Soluble phenanthrene concentrations as the function of Brij 30 (◊), rhamnolipids JBR 204 (■) and Tween 80 (▲) concentrations.
Effect of glucose concentration on the growth of biomass of P. putida DSMZ 8368
The addition of different concentrations of glucose (0, 5, 10 and 50 g L-1) in preculture was tested. It was demonstrated that the growth of biomass of P. putida DSMZ 8368 in batch cultures in the presence of phenanthrene (50 mg L-1) and Brij 30 (0.5 g L-1) issued from precultures containing 50 g L-1 of glucose was significantly higher than in all the other cases (Fig. SM2). Taking into account low biomass accumulation observed from 0 to 10 g L-1 of glucose in preculture, it was supposed that the efficiency of phenanthrenedegradation would be less important. Indeed, two times less phenanthrene was degraded by P. putida DSMZ issued from precultures containing 10 g L-1 of glucose as compared to those with 50 g L-1. It was therefore decided to carry out precultures only with 50 g L-1.
Figure SM2. Kinetics of biomass of P. putida DSMZ 8368 during batch cultures on phenanthrene (50 mg L-1) in the presence of Brij 30 (0.5 g L-1) issued from precultures containing 0, 5, 10 and 50 g L-1 of glucose.