Degradation of isooctane by Mycobacterium austroafricanum IFP 2173: growth and catabolic pathway

Abstract

Aims: 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. Methods and Results:The selected strain exhibited a rather moderate maximum growth rate (l max ¼ 0AE053 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. Significance and Impact of the Study: Isooctane is a recalcitrant branched alkane. A plausible pathway of its degradation by Myco. austroafricanum was put forward.

Degradation of a Mixture of Hydrocarbons, Gasoline, and Diesel Oil Additives by Rhodococcus aetherivorans and Rhodococcus wratislaviensis

“…It also suggested that in R. wratislaviensis IFP 2016 there may be at least two different alkane hydroxylases: one attacking long-chain alkanes (like hexadecane) and having no capacity toward isooctane and the other attacking short-chain alkanes (like octane) and also isooctane. The biodegradability of isooctane is poorly documented; Mycobacterium austroafricanum IFP 2173 is the only strain for which the capacity to grow on isooctane as a sole carbon and energy source has been characterized, and it was shown by reverse transcription-PCR that this probably involved the expression of an alkB gene (43). It is also interesting that isooctane utilization was reduced considerably by the presence of BTEXs (9).…”

Involvement of Two Latex-Clearing Proteins during Rubber Degradation and Insights into the Subsequent Degradation Pathway Revealed by the Genome Sequence of Gordonia polyisoprenivorans Strain VH2

“…The resulting organic acids are most likely metabolized via ␤-oxidation for several reasons: (i) the occurrence of intermediates identified during rubber degradation by S. coelicolor A1 are explainable through degradation via ␤-oxidation; (ii) inhibition by acrylic acid, a ␤-oxidation-specific inhibitor, was observed in strain A1 (18) and other rubber-degrading strains (72); and (iii) ␤-oxidation is also involved in microbial degradation of branched-chain alkanes, such as isooctane (84), pristane (62), phytane (83), squalane, and squalene. The latter is also known to be metabolized by strain VH2 (14).…”

n-Alkane assimilation and tert-butyl alcohol (TBA) oxidation capacity in Mycobacterium austroafricanum strains

“…This result can be partially attributed to the efficiency of the PCR primer pair (Rhose2/ Rhoas1). These primers, previously designed from the alkB sequence of P. putida GPo1 and located between positions Tyr160/Ile166 and Tyr270/Gly275 (Heiss-Blanquet et al 2005;Solano-Serena et al 2004), were less degenerate than the TS2S/deg1RE primer pair (Smits et al 1999) and amplified a smaller DNA fragment (343 bp instead of 525 bp). The polypeptide sequences, deduced from the nucleotide sequences of the PCR amplified fragments, were compared to the corresponding polypeptide fragments of AlkB from M. tuberculosis H37Rv and P. putida GPoI.…”

“…PCR amplification of the partial alkB gene was performed using the forward primer Rhose2 (5′-ACG-GSC-CAY-TTC-TAC-RTC-G-3′) and the reverse primer Rhoas1 (5′-CCG-TAR-TGY-TCG-AGR-TAG-3′), previously designed (Heiss-Blanquet et al 2005;Solano-Serena et al 2004). Rhose2 and Rhoas1 were located between positions Tyr160/Ile166 and Tyr270/Gly275, respectively, in the alkB sequence of P. putida GPo1.…”