Screening for the ability to produce biosurfactants. When grown in BH with 2% dextrose, 10 of the PAH1 strains decreased the culture medium surface tension below 35 mN/mand stabilized hexadecane-water emulsions. They formed halos on blue agar plates with dextrose and mannitol.These 10 strains also synthesized biosurfactants with naphthalene
or phenanthrene as the sole substrate. When cultured in SWF medium with 2% naphthalene, indications of biosurfactant
production were seen within 3 days of incubation.Hexadecane-emulsifying activity was observed and the surface
tension of the culture supernatants was lowered to between 30 and 35 mN/m after 4 to 6 days, depending on the strain. The amounts of biosurfactants produced were therefore sufficient to reach the lowest possible surface tension, the critical micelle concentration.