STUDIES ON THE MICROBIAL PRODUCTION OF ACRYLIC ACID by RAJEN KANTILAL DALAL

In response to present and future fossil resource depletion, chemicals production from an alternate raw materials base must be considered. The biologically catalysed degradation of photos:ynthetically stored energy, such as starch and ligno-cellulosics, is an important approach for chemicals production. The objective of this study is to increase the productivity of acrylate from propionate, using resting cell suspensions of the obligate anaerobe Clostridium propionicum to catalyse the bioconversion, and to produce acrylate from propionate using metabolic mutants of the facultative aerobe Escherichia coli W. These two organisms were chosen from amongst many hypothesized to possess acrylyl-CoA as a metabolic intermediate. Clostridium propionicum is a unique anaerobe fermenting Land 8-alanine to propionate, acetate and carbon dioxide by a direct reductive pathway in which acrylyl-CoA occurs as a terminal electron acceptor. Preliminary studies conducted to standardize the bioconversion system revealed that cells harvested in late exponential phase of growth were optimally active in the capability to produce acrylate. In experiments designed to determine the factors affecting the duration of acrylate production, the effect of product inhibition, oxygen and alternate electron accepting dye toxicity were examined. 34 mmol/l acrylate was found to totally inhibit the synthesis of acrylate from 200 mmol/l propionate in the presence of air. Under anoxic conditions, the acrylate uptake rate showed first order reaction kinetics; 250 mmol/l acrylate is consumed at an initial specific rate of 4.05 mol/g wet weight cells-h and was found not to inhibit further acrylate uptake or production from propionate.