PRODUCTION OF EXOPOLYSACCHARIDES BY ACINETOBACTER STRAINS IN A CONTROLLED FED-BATCH FERMENTATION PROCESS USING SOAP STOCK OIL (SSO) AS CARBON SOURCE

The production of two extracellular capsular heteropolysaccharides by two different Acinetobacter strains has been studied in separate controlled fermentation processes with a view to their industrial applications as specific dispersing agents. The first, emulsan, is an extracellular polyanionic amphipathic heteropolysaccharide (MW 106 D) made by A. calcoaceticus RAG-1. It forms and stabilizes oil in water emulsions. The other, biodispersan (PS-A2), is another extracellular zwitterionic heteropolysaccharide (MW 51 kD) made by A. calcoaceticus A2. This polysaccharide disperses big solid limestone granules forming μm-size water suspension. Both polysaccharides are synthesized within the cells, exported to their outer surface to form an extracellular cell-associated capsule and released subsequently into the growth medium. The polyemers were produced in a computer-controlled fed-batch intensively aerated fermentation process. A commercially available and cheap fatty acids mixture (soap stock oil) served as the carbon source, and was fed in coordination with the required nitrogen. Two coordinated feed of carbon and nitrogen was operated on the basis of two metabolic correlations: The first correlation related the cell protein produced and the ammonium nitrogen consumed with the outcoming coefficients of 24 and 21 mm NH3/g protein for the emulsan and the biodispersan fermentations respectively. The second correlation linked the consumption of the fatty acids with that of the nitrogen source dictating the appropriate C/N ratio of the feed into the operating fermentor. These ratios were 7.7 g C/g N for the emulsan fermentation and 8.5 g C/g N in the case of the biodispersan production process. The polysaccharides were produced separately under a growth associated pattern in a short fermentation process (40-50 h) at a rate of about 0.7 g emulsan/l-h and 0.25 g biodispersan/l-h. During the fermentations the polysaccharides accumulated to about 25 g/l and 12 g/l of emulsion and the biodispersion respectively. The corresponding yields were about 0.3 g emulsan/g FA and 0.2 g biodispersan/g FA. The rate of oxygen uptake (OUR) by the cells was the major factor affecting the specific rate of the polymers production. A maximal emulsan specific productivity of about 0.08 g emulsan/g cell-h was found at a specific oxygen uptake rate of about 10 mm 02/g cell-h. A direct relationship was observed between the biodispersan specific productivity and the specific O2 uptake of the relevant producing cell. Enhancing oxygen transfer rate by elevation of oxygen driving force enabled maintenance of high level of specific OUR of about 12 mm O2/g cell-h, elevating the biodispersan productivity to about 0.5 g biodispersan/l-h. © 1990.