Fig. 1

Identification of biosurfactant activity in mixed microbial cultures derived from oil sludge. a Surfactant activity is detected in supernatant of cultures originated from oil sludge. X- and Y-axis indicate the time and cell density (OD₆₀₀) of the culture. Inset indicates the surface tension (mN/m) at various time points. The horizontal dash line indicates the surface tension of the fresh medium. b Dynamics of individual microbial populations. TFL-RFLP analysis of oil sludge-derived cultures at various time points. Arrowhead and arrow indicate the initial (at 0 h) and final (at 64 h) microbial populations, respectively. c Characterization of microbial isolates from cultures 64 h after growth. TFL-RFLP analysis of individual isolates, identical to those observed at 64 h in (B). d Biosurfactant activity produced by individual isolates. Surface tension of individual isolate cultures (black square) and fresh medium (grey square)