Investigations into the azo reducing activity of a common colonic microorganism

This work was undertaken to study some factors affecting the bacterial reduction (cleavage) of azo compounds, knowledge of which will be of use in the development of azo cross-linked polymers for colon-specific drug delivery. A common colonic bacterium, Bacteroides fragilis was used as test organism and the reduction of azo dyes amaranth, Orange II and tartrazine were studied; also a model azo compound, 4,4'-dihydroxyazobenzene. It was found that the azo compounds were reduced at different rates and the rate of reduction could be correlated with the half-wave (redox) potential of the azo compounds. 4,4'-Dihydroxyazobenzene (E-1/2-470 mV) was reduced at the fastest rate of 0.75 mol l(-1) h(-1), amaranth (E-1/2-568 mV) at 0.30 mol l(-1) h(-1), Orange II (E-1/2-648 mV) at 0.2 mol l(-1) h(-1) and tartrazine (E-1/2-700 mV) at 0.08 mol l(-1) h(-1). Similar observations were made with another colonic bacterium Eubacterium limosum. Reduction of 4,4'-dihydroxyazobenzene did not occur under conditions of aeration, but was enhanced by the low molecular weight electron carrier benzyl viologen, with time for 50% azo reduction being decreased from 120 min to 30 min. These studies with a common, numerically important, colonic bacterium indicate that the reduction of an azopolymer may be influenced by the chemical nature of the azo compound used as cross-linker. (C) 1997 Elsevier Science B.V.