THE EFFECT OF CHEMICAL TREATMENT OF STAINLESS-STEEL WIRE SURFACES ON ZYMOMONAS-MOBILIS CELL ATTACHMENT AND PRODUCT SYNTHESIS

The attachment, growth and product synthesis of non-flocculating Zymom onas mobilis cells, fixed in stainless steel wire spheres CNS), were i nvestigated. The carrier surface was activated by treatment with titan ium (IV) chloride (TiCl4) and gamma-aminopropyltriethoxysilane (AS) in an attempt to raise the efficiency in the immobilization of the cells . System productivity for ethanol and levan production, using cells im mobilized on a modified stainless steel surface in the batch fermentat ion of a sucrose medium, rose as a result of increased biomass compare d to the productivity of cells fixed on untreated (control) metal surf aces. Stabilized ethanol synthesis was demonstrated in the course of f our cycles teach cycle 48 h) of repeated fermentations with a stainles s steel carrier treated with AS, and three cycles when TiCl4 was used. Levan synthesis decreased after three cycles with cells immobilized o n a silanized surface. System productivity for ethanol and levan produ ction after the fourth cycle in experiments with TiCl4-activated, sila nized and unmodified carriers were Qeth = 1.01, 1.06 and 0.27 g/l x h; Q(lev) = 0.32, 0.29 and 0.12 g/l x h, respectively. However, the spec ific productivity of biomass for product synthesis was higher in ferme ntation systems with untreated stainless steel surfaces, probably due to some loss of physiological activity of cells attached to a modified carrier. Investigations of thoroughly washed activated stainless stee l wire surfaces, by scanning electron microscopy after immobilization, showed significant attachment of cells to the carriers. A polymer lay er covered the wire surface treated with TiCl4 after fermentations. Th is may be explained as the binding of extracellular polysaccharide, su ch as the fructose-polymer levan and yeast extract components, to the modified support via chelation. After four fermentations, craters and holes in the polymer layer were evident, probably as a result of CO2 f ormation. A small number of cells appeared on this layer. In view of t he good ethanol formation during all fermentation cycles, it is probab ly that active Z. mobilis cells remained under the polymer layer. Wire treatment with AS resulted in the formation of long filamentous cells during fermentation and some disturbance of cellular fission. This ma y be partly explained by strong electrostatic interactions between the positively charged carrier surface and the predominately negatively c harged surface of Z mobilis cells. However, this did not significantly affect other cellular functions. The surface of the wire treated with AS was practically without a polymer layer.