Degradation of isooctane by Mycobacterium austroafricanum IFP 2173: growth and catabolic pathway.
OBJECTIVE
Isooctane (2,2,4-trimethylpentane), a major component of gasoline formulations, is recalcitrant to biodegradation probably because of the quaternary carbon group it contains. Information on the biodegradability of this hydrocarbon is essential to evaluate its fate in the environment. For these reasons, the degradation kinetics and the catabolic pathway of isooctane were investigated in Mycobacterium austroafricanum IFP 2173, the only strain characterized to use it as sole carbon and energy source.


RESULTS
The selected strain exhibited a rather moderate maximum growth rate (micromax = 0.053 h(-1)) but degraded isooctane up to 99% with a mineralization yield of 45%, indicating attack of the quaternary carbon group. The GC/MS identification of metabolites, 2,4,4-trimethylpentanoic and dimethylpropanoic (pivalic) acids, which transiently accumulated in the cultures indicated that degradation started from the isopropyl extremity of the molecule and subsequently proceeded by catabolism of the tert-butyl moiety. The degradation of putative metabolic intermediates was investigated. The initial isooctane oxidation system was tentatively characterized.


CONCLUSIONS
The isooctane-degrading strain harboured two candidate systems for initial alkane oxidation. Although a cytochrome P450 was induced by isooctane degradation, the functional oxidation system was probably a nonheme alkane monooxygenase as indicated by PCR amplification and RT-PCR expression of an alkB gene.


CONCLUSIONS
Isooctane is a recalcitrant branched alkane. A plausible pathway of its degradation by Myco. austroafricanum was put forward.
Département de Microbiologie, Institut Français du Pétrole, Rueil-Malmaison, France. remy.marchal@ifp.fr
F
F
Solano-Serena
R
R
Marchal
S
S
Heiss
J-P
JP
Vandecasteele
D000473:Alkanes / Q000378:metabolism; D001673:Biodegradation, Environmental; D018533:Biomass; D002245:Carbon Dioxide / Q000378:metabolism; D003470:Culture Media; D042926:Cytochrome P-450 CYP4A / Q000032:analysis / Q000235:genetics; D003577:Cytochrome P-450 Enzyme System / Q000032:analysis; D004781:Environmental Exposure; D008401:Gas Chromatography-Mass Spectrometry / Q000379:methods; D005742:Gasoline; D005798:Genes, Bacterial / Q000235:genetics; D008314:Malonates / Q000378:metabolism; D009161:Mycobacterium / Q000254:growth & development / Q000378:metabolism*; D009795:Octanes / Q000378:metabolism*; D010421:Pentanoic Acids / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods
D000473:Alkanes; D003470:Culture Media; D005742:Gasoline; D008314:Malonates; D009795:Octanes; D010421:Pentanoic Acids; D002245:Carbon Dioxide; C005566:pivalic acid; D003577:Cytochrome P-450 Enzyme System; C030290:malonic acid; D042926:Cytochrome P-450 CYP4A; C045798:2,2,4-trimethylpentane