RHAMNOLIPID PRODUCTION IN SMALL BED DEPTH STATIC-SUBMERGED FERMENTATION USING MEMBRANES OF BACTERIAL CELLULOSE AS SOLID SUPPORT

Rhamnolipids are microbial surfactants that exhibit low toxicity, biodegradability and high ecological acceptability. These compounds are among of the most studied and promising biosurfactants, however when compared with their chemical congeners, high production costs are still a limiting factor for their application in the market. Rhamnolipid production by submerged fermentation using membranes of bacterial cellulose as solid support (SbF-BCM) is a promising process to obtain these compounds. This process presents the advantage of avoid foaming, which is a serious problem of biosurfactant production, in the classical submerged fermentation, reflecting in the loss of biomass and nutrients, reduction of production rates or even making the process infeasible. Another advantage is the low operating cost, since bacterial cellulose membranes are autoclavable and reusable. The present work aimed to evaluate the influence of the bed depth and the presence of agitation (200 rpm) on the production of rhamnolipids by Pseudomonas aeruginosa PAO1 using SbF-BCM fermentative technology. The bed depth of SbF-BCM, in static condition, was evaluated on 125 mL Erlenmeyers flasks containing 2 mL to 20 mL of fermented medium. The production of rhamnolipids reached by small bed depths (2 mL to 5 mL) was higher than those reached by large bed depth (8 mL to 20 mL), being the best yield reached with 3 mL of fermented medium (5.1 g/L) ), which might be related to difficulties of gaseous transferring rate on statics cultivation in large bed depth. The necessity of the presence of the membrane of bacterial cellulose as support was checked in static cultivation of small bed by the presence or absence of the membrane in the cultivations. Only 69 % of the yield of rhamnolipid obtained by SbF-BCM technology was reached in the cultivations with absence of the bacterial cellulose membrane. The benefits of this support might be related to the composition of those membranes (99 % of water), which might keep moisture and help diffusion of nutrients. Finally, we compared SbF-BCM in static and agitated condition. Agitation had a negative influence on rhamnolipid production by SbF-BCM in large bed depth (50 % reduction) and did not show significant influence on SbF-BCM in small bed depth. Our results suggest that static-submerged fermentation using membranes of bacterial cellulose as solid support in small bed depth cultivations presents great potential to make biotechnological production of surfactants feasible.