Micelle size characterization of lipopeptides produced by B. subtilis and their recovery by the two-step ultrafiltration process

Abstract

The aim of this work was to investigate the lipopeptides aggregation behavior in single and mixed solutions in a wide range of concentrations, in order to optimize their separation and purification following the two-step ultrafiltration process and using large pore size membranes (up to MWCO=300kDa). Micelle size was determined by dynamic light scattering. In single solutions of lipopeptide both surfactin and mycosubtilin formed micelles of different size depending on their concentration, micelles of average diameter=5–105nm for surfactin and 8–18nm for mycosubtilin. However when the lipopeptides were in the same solution they formed mixed micelles of different size (d=8nm) and probably conformation to that formed by the individual lipopeptide, this prevents their separation according to size. These lipopeptides were purified from fermentation culture by the two-step ultrafiltration process using different MWCO membranes ranging from 10 to 300kDa. This led to their effective rejection in the first ultrafiltration step by membranes with MCWO=10–100kDa but poor rejection by the 300KDa membrane. The lipopeptides were recovered at 90% purity (in relation to protein) and with 2.34 enrichment in the permeate of the second ultrafiltration step with the 100KDa membrane upon addition of 75% ethanol.