Measurement of Surface Tension of a Microbial Culture Producing Biosurfactants on N-Alkanes: A Critical Analysis of the Current Methodology

The present work reveals, on theoretical basis, that results from measurments of boundary tension of the n-alkane whole broth per se are likely to be inconclusive as to wheather the produced surfactant is extracellular or is cell-associated. Using an isolated Micrococcus species, this study critically examined the influence of the upper floating layer of whole broth on the surface tension arising from the extracellularly produced water soluble biosurfactant. It has also been seen that the observed change in surface tension of the whole broth following serial dilution is not due to the dilution of the produced surfactants in the true sense. Rather, it is due to the progressive removal of the interfering upper layer in parts during the process of serial dilution. Moreover, the extent of dilution of whole broth required to arrive at the CMC (as followed by others) was found to be influenced largely by the quantum of biomass rather than the lipid present in the floating layer.