TABLE 1.

¹³C/¹²C and D/H isotope fractionation by different aerobic bacterial strains during growth with aromatic hydrocarbons^a

Strain	Enzyme mechanism	Carbon source	ɛCn	ɛDl
P. putida strain mt-2	Methyl monooxygenase	Toluene	−3.3 ± 0.3	−905 ± 71
	Methyl monooxygenase	m-Xylene	−1.7 ± 0.04	NDb
	Methyl monooxygenase	p-Xylene	−2.3 ± 0.3	ND
R. pickettii strain PKO1	Ring monoooxygenase	Toluene	−1.1 ± 0.2	−16 ± 5.3
P. putida strain F1	Ring dioxygenase	Toluene	−0.4 ± 0.3	−28 ± 10
P. putida strain NCIB 9816	Ring dioxygenase	Naphthalene	−0.1 ± 0.2	−65 ± 13

^aStable carbon isotope fractionation is given as the enrichment factor, ɛ_n, and was calculated with equations 1 and 2. Hydrogen isotope fractionation with mixtures (50:50) of per-deuterated and nonlabeled substrate was determined with equation 3. The enrichment factor for labeled substances, ɛ₁, was determined by equation 2. Mean values ± standard deviation are given based on three independent growth experiments with fivefold isotope analysis per data point.

^bND, not determined.