Abstract The metabolism of biphenyl by Mycobacteri- um sp. PYR-1 was investigated. The Mycobacterium sp. degraded >98% of the biphenyl added within 72 h. Anal- ysis of ethyl acetate extracts of the culture medium by HPLC indicated that benzoic acid was the major metabo- lite. Other products were 4-hydroxybiphenyl, 4-hydroxy- benzoic acid, and 5-oxo-5-phenylpentanoic acid. The metabolites were characterized by mass and 1 H NMR spectrometry. Identification of benzoic acid and 5-oxo-5- phenylpentanoic acid indicates that biphenyl degradation by Mycobacterium sp. PYR-1 is generally similar to known pathways. A novel alternative metabolic pathway consisted of monooxygenation at C-4 of biphenyl to give 4-hydroxybiphenyl, with subsequent degradation via ring cleavage to 4-hydroxybenzoic acid. Introduction Biphenyl is a natural component of coal tar, crude oil, and natural gas. It has been used in chemical synthesis of emulsifiers, optical brighteners, crop protection prod- ucts, and plastics; in dyeing of polyesters; as a fungistat for citrus fruits; as a heat transfer agent; as a dyestuff carrier for textiles and copying paper; as a solvent for pharmaceuticals; and as the parent compound for poly- chlorinated biphenyls (PCBs) (Hawley 1971; Weaver et al. 1979). Biphenyl enters the atmosphere from the burn- ing of oil, coal, and gasoline, and is emitted in exhaust air from residential and industrial heating systems (Boehncke et al. 1999). The use of biphenyl has declined greatly over time, but it is still present as a contaminant in the environment. Therefore, many studies have been undertaken to examine its toxicological properties and environmental fate. There are no data proving that biphe- nyl is a teratogen, but animal studies indicate that it pro- duces morphological and histopathological changes in the urinary system (Boehncke et al. 1999). In vitro stud- ies indicate that it has mutagenic potential and since reli- able results from in vivo tests are lacking, biphenyl must be considered a possible mutagen (Boehncke et al. 1999). Chronic exposure to biphenyl in the diet has been reported to cause kidney disorders, reduced hemoglobin levels, decreased appetite and growth, reduced life span (Ambrose et al. 1960), and bladder cancer (Boehncke et al. 1999) in animals. Acute exposure to high levels of bi- phenyl can cause slight eye irritation, hepatotoxicity, and toxic effects on the central and peripheral nervous sys- tems (Sandmeyer 1981). Workers in a biphenyl paper and citrus packing plant exposed to biphenyl vapors re- ported inflammation of the respiratory tract, headache, nausea, hepatitis, and even death in one case (Boehncke et al. 1999). There is an abundance of information on the bacterial degradation of biphenyl. The usual mode of attack on bi- phenyl begins with the formation of a cis-dihydrodiol, followed by dehydrogenation to a dihydroxybiphenyl (Catelani et al. 1973; Gibson et al. 1973; Haddock et al. 1993). The ring may be cleaved to form 2-hydroxy-6- keto-6-phenylhexa-2,4-dienoic acid (HOPDA), which is cleaved again to form benzoic acid and a five-carbon fragment (Catelani et al. 1973; Omori et al. 1986b). Al- ternatively, the double bonds of HOPDA may be hydro- genated, and then an aldehyde is formed and oxidized to a carboxylic acid (Omori et al. 1988). Gram-positive nocardioform bacteria have been shown to degrade biphenyl. Recently, Wagner-Döbler et J.D. Moody · C.E. Cerniglia ( ✉ ) Division of Microbiology, National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson, AR 72079 USA e-mail: CCerniglia@nctr.fda.gov Tel.: +1-870-5437341, Fax: +1-870-5437307 D.R. Doerge Division of Biochemical Toxicology, National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson, AR 72079 USA J.P. Freeman Division of Chemistry, National Center for Toxicological Research, U.S. Food and Drug Administration, Jefferson, AR 72079 USA Appl Microbiol Biotechnol (2002) 58:364–369 DOI 10.1007/s00253-001-0878-3 ORIGINAL PAPER J.D. Moody · D.R. Doerge · J.P. Freeman C.E. Cerniglia Degradation of biphenyl by Mycobacterium sp. strain PYR-1 Received: 27 July 2001 / Revised: 3 October 2001 / Accepted: 19 October 2001 / Published online: 21 December 2001 © Springer-Verlag 2001