Biodegradation of dibenzofuran and dioxins by Pseudomonas aeruginosa and Xanthomonas maltophilia

This study was aimed at finding microorganisms capable of biodegrading diox ins efficiently to develop a biotechnological treatment for decomposition o f dioxins. Dibenzofuran(DBF) was used as a test substance to cultivate and to screen microbes active in degrading dioxins. Two microbial species (Pseu domonas aeruginosa and Xanthomonas maltophilia) which could degrade DBF wer e isolated from the sludge of a Kraft pulp mill wastewater treatment plant. The optimal conditions for biodegrading DBF were 30 and pH:7. Ps. aerugino sa, which had a high growth rate with DBF as carbon source showed high grow th rates in the presence of such dioxins as dibenzo-p-dioxin, medium growth with 1-chlorodibenzo-p-dioxin, 2-chlorodibenzo-p-dioxin and 2,8-dichlorodi benzofuran, low growth with 2,6-dichlorodibenzo-p-dioxin and 1,2,3,4-tetrac hlorodibenzo-p-dioxin and no growth with octachlorodibenzofuran. These resu lts suggested that the growth rate of Ps. aeruginosa using dioxins as carbo n source decreased with the increase in the degree of chlorine substitution . Activity of Ps. aeruginosa biodegrading dioxins was high for DBF, dibenzo -p-dioxin and 1-chlorodibenzo-p-dioxin and low for 2,8-dichlorodibenzofuran , 3,6-dichlorodibenzofuran, 2-chlorodibenzo-p-dioxin and 2,6-dichlorodibenz o-p-dioxin. These results suggested that there is a correlation between gro wth and the ability to biodegrade dioxins; On the other hand, the efficienc y in the biodegradation of 1,2,3,4-tetrachlorodibenzo-p-dioxin was comparat ively high although the growth rate on this dioxin was low. Hydroxydibenzof uran, 2-hydroxy-3-allyl-benzofuran and 2-carboxyvinyloxy phenyl acetic acid were identified by gas chromatograph-mass spectrometry (GC/MS) as products of DBF biodegradation by Ps. aeruginosa, suggesting a possible biodegradat ion pathway for dioxins.