Screening of biosurfactant-producing Bacillus strains using glycerol from the biodiesel synthesis as main carbon source.

Glycerol, a co-product of biodiesel production, was evaluated as carbon source for biosurfactant production. For this reason, seven non-pathogenic biosurfactant-producing Bacillus strains, isolated from the tank of chlorination at the Wastewater Treatment Plant at Federal University of Ceara, were screened. The production of biosurfactant was verified by determining the surface tension value, as well as the emulsifying capacity of the free-cell broth against soy oil, kerosene and N-hexadecane. Best results were achieved when using LAMI005 and LAMI009 strains, whose biosurfactant reduced the surface tension of the broth to 28.8 ± 0.0 and 27.1 ± 0.1 mN m(-1), respectively. Additionally, at 72 h of cultivation, 441.06 and 267.56 mg L(-1) of surfactin were produced by LAMI005 and LAMI009, respectively. The biosurfactants were capable of forming stable emulsions with various hydrocarbons, such as soy oil and kerosene. Analyses carried out with high performance liquid chromatography (HPLC) showed that the biosurfactant produced by Bacillus subtilis LAMI009 and LAMI005 was compatible with the commercially available surfactin standard. The values of minimum surface tension and the CMC of the produced biosurfactant indicated that it is feasible to produce biosurfactants from a residual and renewable and low-cost carbon source, such as glycerol.

Influence of mass transfer limitations on the enzymatic synthesis of beta-lactam antibiotics catalyzed by penicillin G acylase immobilized on glioxil-agarose.

Mass transfer effects were investigated for the synthesis of ampicillin and amoxicillin, at pH 6.5 and 25 degrees C, catalyzed by penicillin G acylase immobilized on agarose. The influence of external mass transfer was analysed using different stirring rates, ranging form 200 to 800 rpm. Above 400 rpm, the film resistance may be neglected. Intra-particle diffusion limitation was investigated using biocatalysts prepared with different enzyme loads and agarose with different mean pore diameters. When agarose with 6, 8 and 10% of crosslinking were used, for the same enzyme load, substrates and products concentration profiles presented no expressive differences, suggesting pore diameter is not important parameter. An increase on enzyme load showed that when more than 90 IU of enzyme activity were used per mL of support, the system was influenced by intra-particle mass transfer. A reactive-diffusive model was used to estimate effective diffusivities of substrates and products.