Microfiltration of Bacillus sp. cultivation broths based on commercial and raw glycerol

Bacteria of the genus Bacillus are well known as the producers of wide spectra of different metabolites with antimicrobial activity against different pathogens. The biomass of Bacillus spp. can also contribute to the overall antimicrobial activity due to ability of these bacteria to rapidly adjust to different ecological and nutritional conditions and therefore their ability to supress competing microorganisms. These beneficial characteristics of the genus Bacillus are nowadays employed in order to produce efficient and economically viable biocontrol products that could be used for management of different plant diseases caused by microbial phytopathogens. In this study, cross-flow microfiltration using ceramic membrane was employed for separation of Bacillus sp. biomass from cultivation broths obtained after cultivation on media containing commercial and raw glycerol from biodiesel production as carbon sources. Cultivations were carried out in a laboratory scale bioreactor under the similar conditions (96 h, 28 ºC, 250 rpm, 1 vvm). Microfiltration was performed with transmembrane pressure of 0.6 bar and feed flow rate of 60 L/h, while permeate flux was measured during the experiment. Furthermore, antimicrobial activities of the obtained cultivation broths were tested against two Xanthomonas campestris phytopathogenic strains, known for infecting crucifers, pepper and tomato, using the diffusion-disc method. The results of this study point out that higher values of permeate flux were observed in the case of microfiltration of cultivation broth based on commercial glycerol, due to the larger amount of suspended impurities present in the raw glycerol. Larger inhibition zone diameters were also obtained for the cultivation broth based on commercial glycerol, indicating that this type of glycerol has been better choice for cultivation of Bacillus sp. However, antimicrobial activity of cultivation broth based on raw glycerol also suggests that this byproduct of biodiesel industry could be successfully used as carbon source in this type of microbial conversion.