Biosurfactant production by Serratia marcescens SS-1 and its isogenic strain SMΔR defective in SpnR, a quorum-sensing LuxR family protein

Serratia marcescens SS-1 and its SpnR-defective isogenic mutant, SMΔR, produced an extracellular surfactant able to decrease surface tension of water from 72 to 37 dyne cm^-1 (SMΔR strain) and to 45 dyne cm^-1 (SS-1 strain). The biosurfactant also emulsified kerosene and diesel with a maximum emulsion index of 77% (diesel and kerosene) for the SMΔR strain, and 72% (kerosene) and 40% (diesel) for the SS-1 strain. Deletion of spnR gene appeared to enhance biosurfactant production. Model simulations suggest that biosurfactant production by the two strains was growth-associated. The SMAR strain had a yield coefficient of 22-32% g dry cell^-1, which is 32-50% higher than that of the SS-1 strain.