Bioreactor cultivation of a thermophilic bacterium capable of degrading BTEX

The thermophillic bacterium, Thermus species ATCC 27978, which is capable iof degrading the fuel-spill contaminants benzene, toluene, ethylbenzene, and the xylenes (BTEX) was cultured in 5-L-bioreactors. The goal was to optimize the production of Thermus sp. cells possessing maximal degradative activity for their subsequent potential application in a thermally-enhanced in situ BTEX bioremediation process. The effects of two bioreactor cultivation modes, batch and fed batch, on the generation of BTEX-active biomass were investigated. More biomass and more thermophillic BTEX-degrading activity were produced in the fed-batch cultures than in the batch cultures. Catabolite inhibition or repression is the cause for the limited growth of Thermus sp. in batch reactors. However, the addition to the medium of O-cresol, a possible intermediate in BTEX metabolism, stabilized the cellular BTEX-degrading activity in such cultures. The fed-batch mode of cultivations yielded a biomass concentration of 2.5 g/L and a catalytic specific activities of 7.6 {+-} 1.3, 10.1 {+-} 1.9. 9.8 {+-} 2.1, 2.3 {+-} 0.5, and 4.6 {+-} 0.9 nmol of compound degraded/mg of dry cell wt-min at 60{degrees}C for benzene, toluene, ethylbenzene, m-xylene, and the o-plus p-xylenes (unresolved mixture), respectively. Although the formation of BTEX-degrading activity is growth associated, the prior rate of bioreactormore » growth affects the level of susequent washed, whole-cell BTEX-degrading activity. A slow to moderate specific growth rate (0.02-0.07 h{sup -1}) favors the formation of cellular BTEX-degrading activity, while a high specific growth rate ({approx}0.16 h{sup -1}) is detrimental to its production.« less