title: Biodegradation of high-concentration isopropanol by a solvent-tolerant thermophile, Bacillus pallidus.
abstract: The aerobic biodegradation of high-concentration, to 24 g l(-1), 2-propanol (IPA) by a thermophilic isolate ST3, identified as Bacillus pallidus, was successfully carried out for the first time. This solvent-tolerant B. pallidus utilized IPA as the sole carbon source within a minimal salts medium. Cultivation was carried out in 100-ml shake flasks at 60 degrees C and compared with cultivation within a 1-l stirred tank reactor (STR). Specific growth rate (micro) was about 0.2 h(-1) for both systems, with a maximum cell density of 2.4 x 10(8) cells ml(-1) obtained with STR cultivation. During exponential growth and stationary phase, IPA biodegradation rates were found to be 0.14 and 0.02 g l(-1) h(-1), respectively, in shake-flask experiments, whereas corresponding values of 0.09 and 0.018 g l(-1) h(-1) were achievable in the STR. Generation of acetone, the major intermediate in aerobic IPA biodegradation, was also monitored as an indicator of microbial IPA utilization. Acetone levels reached a maximum of 2.2-2.3 g l(-1) after 72 and 58 h for 100-ml and 1-l systems, respectively. Both IPA and acetone were completely removed from the medium following 160 and 175 h, respectively, during STR growth, although this was not demonstrated within shake-flask reactions. Growth of B. pallidus on acetone or IPA alone demonstrated that the maximum growth rate ( micro ) obtainable was 0.247 h(-1) at 4 g l(-1) acetone and 0.202 h(-1) at 8 g l(-1) IPA within shake-flask cultivation. These results indicate the potential of the solvent-tolerant thermophile B. pallidus ST3 in the bioremediation of hot solvent-containing industrial waste streams.
authors.affiliation: Department of Mechanical and Chemical Engineering, Heriot-Watt University, Riccarton, Edinburgh EH14 4AS, UK.
authors.forename: Mark T
authors.initials: MT
authors.lastname: Bustard
authors.forename: Samantha
authors.initials: S
authors.lastname: Whiting
authors.forename: Don A
authors.initials: DA
authors.lastname: Cowan
authors.forename: Phillip C
authors.initials: PC
authors.lastname: Wright
mesh_terms: D019840:2-Propanol / Q000378:metabolism*; D000222:Adaptation, Physiological; D001407:Bacillus / Q000378:metabolism* / Q000502:physiology; D001673:Biodegradation, Environmental; D005285:Fermentation
chemical_list: D019840:2-Propanol