META-PATHWAY DEGRADATION OF PHENOLICS BY THERMOPHILIC BACILLI

Thermophilic bacteria capable of degrading phenol as the sole carbon s ource were isolated from sewage effluent. The isolates were aerobic. s porulating, motile rod-shaped bacteria characterized as Bacillus speci es with growth temperature optima of 50-60 degrees C. The enzyme catal yzing the second step in the phenol degradation meta-cleavage pathway, catechol-2,3-dioxygenase, was detected in all isolates grown in the p resence of phenol. One strain, designated Bacillus strain Cro3.2, was capable of degrading phenol, o-, m-, and p-cresol via the meta-pathway and tolerated phenol at concentrations up to 0.1% (w/v) without appar ent inhibition of growth. Phenol degradation activities in strain Cro3 .2 were induced 3-5 h after supplementation by phenol, orcinol, and th e cresols bur not by halo- or nitro-substituted phenols. Maximal rates of phenol degradation in stirred bioreactors (10 mu mol/min(-1)/g(-1) cells) were achieved at an O-2 delivery rate of 1.0 vvm and temperatu res of 45-60 degrees C; however, catechol-2,3-dioxygenase (bur not 2-h ydroxymuconic semialdehyde dehydrogenase) was rapidly inactivated at h igh oxygen concentrations. Whole cells of Bacillus strain Cro3.2 entra pped in calcium alginate, polyacrylamide, and agarose gels showed wide ly different rates of phenol degradation. In calcium alginate gels, ra pid loss of phenol-degrading activity was attributed to calcium-induce d inactivation of catechol-2,3-dioxygenase. No stabilization with resp ect to oxygen-induced inactivation was observed under any of the immob ilization conditions. It is concluded that the counteractive effects o f oxygen limitation at low dO(2) and inactivation of catechol-2,3-diox ygenase at high dO(2) levels pose a significant impediment to the use of resting thermophile cells in the treatment of phenolic waste stream s. (C) 1998 Elsevier Science Inc.