Abstract
In order to develop and optimize a syngas fermentation using a hollow fiber membrane bioreactor (HFMB), this study proposes to characterize the surface of Clostridium carboxidivorans, a strictly anaerobic and gram- positive bacterium capable of producing biofuels and other chemicals. The choice for using syngas as substrate arises from the necessity to give a better destination to urban and industrial residues, which are destined to landfills. In a HFMB, a Clostridium carboxidivorans biofilm can be used for the purpose of enhancing cell density in the system, which is normally a problem for anaerobe bacterium; and the membrane can increase the mass transfer coefficient, a bottleneck in this process due to the gas-liquid mass transfer. The knowledge of the interactions between cells and surfaces, cell hydrophobicity and/or hydrophilicity, and how to enhance the force balance between electrostatic and van der Waals interactions, could enhance celladhesion, biofilm formation and cell interaction with substrate. The Contact Angle Measurement (CAM) showed that C. carboxidivorans have a total surface tension (?TOT) of 56.0 mJ m-2, and its components: Lifshitz-van der Waals (?LW) of 24.3 mJ m-2 and Lewis acid-base (?AB) of 31.7 mJ m-2. Also, the free energy of interaction between cells and water (?Gmwm) was 9.6 mJ m-2 and the free energy of interaction between cells and hexadecane when immersed in water (?Gmwh) was -14.7 mJ m-2. With these values, it was possible to determine that Clostridium carboxidivorans presents a hydrophilic surface character but is also capable ofbeing attracted by hydrophobic molecules, liquids and surfaces and capable of interacting with them when immersed in water. Moreover, Clostridium carboxidivorans presented an electron-donor character, which already appeared in previous studies but was confirmed with this test. Therefore, this strain, when immersed in an aqueous culture medium, has an affinity to a hydrophobic membrane, which would favor its adhesion.
