Thermophilic biodegradation of BTEX by two Thermus Species

Abstract

Two thermophilic bacteria, Thermus aquaticus ATCC 25104 and Thermus species ATCC 27978, were investigated for their abilities to degrade BTEX (benzene, toluene, ethylbenzene, and xylenes). Thermus aquaticus and the Thermus sp. were grown in a nominal medium at 70°C and 60°C, respectively, and resting cell suspensions were used to study BTEX biodegradation at the same corresponding temperatures. The degradation of BTEX by these cell suspensions was measured in sealed serum bottles against controls that also displayed significant abiotic removals of BTEX under such high-temperature conditions. For T. aquaticus at a suspension density of only 1.3 x 10⁷ cells/mL and an aqueous total BTEX concentration of 2.04 mg/L (0.022 mM), benzene, toluene, ethylbenzene, m-xylene, and an unresolved mixture of o-and p-xylenes were biodegraded by 10, 12, 18, 20, and 20%, respectively, after 45 days of incubation at 70°C. For the Thermus sp. at a suspension density of 1.1 x 10⁷ cells/mL and an aqueous total BTEX concentration of 6.98 mg/L (0.079 mM), benzene, toluene, ethylbenzene, m-xylene, and the unresolved mixture of o-and p-xylenes were biodegraded by 40, 35, 32, 33, and 33%, respectively, after 45 days of incubation at 60°C. Raising the BTEX concentrations lowered the extents of biodegradation. The biodegradations of both benzene and toluene were enhanced when T. aquaticus and the Thermus sp. were pregrown on catechol and o-cresol, respectively, as carbon sources. Use of [U-¹⁴C]benzene and [ring-¹⁴C]toluene verified that a small fraction of these two compounds was metabolized within 7 days to water-soluble products and CO₂ by these nongrowing cell suspensions. Our investigation also revealed that the nominal medium can be simplified by eliminating the yeast extract and using a higher tryptone concentration (0.2%) without affecting the growth and BTEX degrading activities of these cells. © 1995 John Wiley & Sons, Inc.