Abstract
A total of 11 bacterial strains capable of completely degrading 2-butoxyethanol (2-BE) were isolated from forest soil, a biotrickling filter, a bioscrubber, and activated sludge, and identified by 16S rRNA gene sequence analysis. Eight of these strains belong to the genus Pseudomonas; the remaining three strains are Hydrogenophaga pseudoflava BOE3, Gordonia terrae BOE5, and Cupriavidus oxalaticus BOE300. In addition to 2-BE, all isolated strains were able to grow on 2-ethoxyethanol and 2-propoxyethanol, ethanol, n-hexanol, ethyl acetate, 2-butoxyacetic acid (2-BAA), glyoxylic acid, and n-butanol. Apart from the only gram-positive strain isolated, BOE5, none of the strains were able to grow on the nonpolar ethers diethyl ether, di-n-butyl ether, n-butyl vinyl ether, and dibenzyl ether, as well as on 1-butoxy-2-propanol. Strains H. pseudoflava BOE3 and two of the isolated pseudomonads, Pseudomonas putida BOE100 and P. vancouverensis BOE200, were studied in more detail. The maximum growth rates of strains BOE3, BOE100, and BOE200 at 30 °C were 0.204 h−1 at 4 mM, 0.645 h−1 at 5 mM, and 0.395 h−1 at 6 mM 2-BE, respectively. 2-BAA, n-butanol, and butanoic acid were detected as potential metabolites during the degradation of 2-BE. These findings indicate that the degradation of 2-BE by the isolated gram-negative strains proceeds via oxidation to 2-BAA with subsequent cleavage of the ether bond yielding glyoxylate and n-butanol. Since Gordonia terrae BOE5 was the only strain able to degrade nonpolar ethers like diethyl ether, the degradation pathway of 2-BE may be different for this strain.
Highlights
2-Butoxyethanol (2-BE), called ethylene glycol monobutyl ether, is a widely used organic compound, which does not occur naturally
Germany e-mail: christine.woiski@iswa.uni-stuttgart.de strains BOE3, BOE100, and BOE200 at 30 °C were 0.204 h-1 at 4 mM, 0.645 h-1 at 5 mM, and 0.395 h-1 at 6 mM 2-BE, respectively. 2-butoxyacetic acid (2-BAA), nbutanol, and butanoic acid were detected as potential metabolites during the degradation of 2-BE. These findings indicate that the degradation of 2-BE by the isolated gram-negative strains proceeds via oxidation to 2-BAA with subsequent cleavage of the ether bond yielding glyoxylate and n-butanol
It is classified as a ‘High Production Volume Chemical’ (HPVC) because of its considerable production volumes of approximately 161 kt/a in the EU (2003) and 45–227 kt/a in the USA (2002) (European Chemicals Bureau 2006; OECD 2004). 2-BE is mainly used as a solvent in surface coatings, paints, and varnishes, and in lubricants, oils, and dyes. It is found in detergents and cleaning agents, printing inks, hydrofracking liquids, oil dispersants, textiles, hair dyes, cosmetics, pharmaceutical products, agricultural chemicals, herbicides, brake fluids, de-icers, and extinguishing foams, and serves as a starting chemical for the production of other chemicals such as butyl glycol acetate or various plasticizers (Committee on Energy and Commerce U.S House of Representatives 2011; Gooch 2007; IARC 2006; OECD 1997; U.S EPA 2010). 2-BE is the main component of the oil dispersant Corexit EC9527A (Kover et al 2014). 813,000 L of Corexit EC9527A were applied to the ocean surface during the 2010 Deepwater Horizon oil spill (BP Gulf Science Data 2014)
Summary
2-Butoxyethanol (2-BE), called ethylene glycol monobutyl ether, is a widely used organic compound, which does not occur naturally It is classified as a ‘High Production Volume Chemical’ (HPVC) because of its considerable production volumes of approximately 161 kt/a in the EU (2003) and 45–227 kt/a in the USA (2002) (European Chemicals Bureau 2006; OECD 2004). To a much lesser extent, dealkylation of 2-BE by cytochrome P450 2E1 (CYP 2E1) was observed This reaction leads to the formation of butyraldehyde and ethylene glycol, which is further oxidized to oxalic acid (Rambourg-Schepens et al 1988). Different pathways for the aerobic degradation of ethylene glycol ethers (EGEs) like polyethylene glycol (PEG) or linear primary fatty. Biodegradation (2020) 31:153–169 alcohol ethoxylates (LAEs) on the one hand and linear and cyclic alkyl ethers (AEs) on the other hand have been proposed They can provide information on the possible degradation route of 2-BE. The (hypothetic) degradation of 2-BE according to this pathway is depicted in Fig. 1, route 1
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