Anaerobic oxidation of alkanes by newly isolated denitrifying bacteria
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© Springer-Verlag 2000
O R I G I N A L PA P E R
Petra Ehrenreich · Astrid Behrends · Jens Harder · Friedrich Widdel
Anaerobic oxidation of alkanes by newly isolated denitrifying bacteria
Received: 3 August / Accepted: 6 October 1999
Abstract The capacity of denitrifying bacteria for anaerobic utilization of saturated hydrocarbons (alkanes) was investigated with n-alkanes of various chain lengths and with crude oil in enrichment cultures containing nitrate as electron acceptor. Three distinct types of denitrifying bacteria were isolated in pure culture. A strain (HxN1) with oval-shaped, nonmotile cells originated from a denitrifying enrichment culture with crude oil and was isolated with n-hexane (C6H14). Another strain (OcN1) with slender, rod-shaped, motile cells was isolated from an enrichment culture with n-octane (C8H18). A third strain (HdN1) with oval, somewhat pleomorphic, partly motile cells originated from an enrichment culture with aliphatic mineral oil and was isolated with n-hexadecane (C16H34). Cells of hexane-utilizing strain HxN1 grew homogeneously in the growth medium and did not adhere to the alkane phase, in contrast to the two other strains. Quantification of substrate consumption and cell growth revealed the capacity for complete oxidation of alkanes under strictly anoxic conditions, with nitrate being reduced to dinitrogen. Key words n-Alkanes · Anaerobic hydrocarbon oxidation · Denitrifying bacteria · Isolation · Degradation balance
Introduction Saturated hydrocarbons (alkanes) are widespread compounds in terrestrial and marine environments. Among the hydrocarbons produced in living organisms, several unbranched and methyl-branched alkanes have been identified in addition to various alkenes (Birch and Bachofen 1988). Furthermore, alkanes are formed in sediments from biomolecules in the course of geochemical transforP. Ehrenreich · A. Behrends · J. Harder · F. Widdel (쾷) Max-Planck-Institut für Marine Mikrobiologie, Celsiusstrasse 1, 28359 Bremen, Germany e-mail: [email protected], Tel.: +49-421-2028702, Fax: +49-421-2028790
mation processes (diagenesis and catagenesis), which include elimination of polar groups and saturation of isolated double bonds (Tissot and Welte 1984). These processes lead to the formation of petroleum. Hence, most crude oils are constituted mainly of alkanes (and aromatic hydrocarbons), among which n-alkanes usually dominate (Tissot and Welte 1984). Besides biological production of alkanes, contamination by crude oil and its technically refined products presents an additional, significant source of saturated hydrocarbons in the environment. In contrast to many aromatic hydrocarbons, alkanes are usually not regarded as toxic. Only relatively short-chain alkanes (C5C12) at high concentration may affect biological membranes (Sikkema et al. 1995) and have narcotic effects (Forth et al. 1990). Containing exclusively apolar sigma bonds in the molecule, alkanes belong to the chemically least reactive compounds. Many aerobic alkane-degrading microorganisms have been in
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