The EPR spectra for H/D exchange of the glycyl radical and the reverse exchange were observed in cell extracts of toluene-grown Aromatoleum toluolicum strain T. They were recorded with an EMX-6/1 X-band spectrometer (Bruker, Karlsruhe, Germany) with a standard TE102 rectangular cavity and an ESR-900 helium flow cryostat with variable temperature (Oxford instruments, Oxford, UK) or a liquid-nitrogen finger dewar as described in . The H/D exchange at glycyl radical in D2O was also confirmed by EPR spectra of extracts of toluenegrown cells of an Aromatoleum sp. which were recorded by a Bruker Elexsys E580 spectrometer and SHQ4122 resonator equipped with ESR900 cryostat (Oxford Instruments) (see SI for details).