Resiliency of Stable Isotope Fractionation (δ13C and δ37Cl) of Trichloroethene to Bacterial Growth Physiology and Expression of Key Enzymes

Quantification of in situ (bio)degradation using compoundspecific isotope analysis requires a known and constant isotope enrichment factor (s). Because reported isotope enrichment factors for microbial dehalogenation of chlorinated ethenes vary considerably we studied the potential effects of metabolic adaptation to TCE respiration on isotope fractionation (delta C-13 and delta Cl-37) using a model organism (Desulfitobacterium hafniesne Y51), which only has one reductive dehalogenase (PceA). Cells grown on TCE for the first time showed exponential growth until 10(9) cells/mL. During exponential growth, the cell-normalized amount of PceA enzyme increased steadily in the presence of TCE (up to 21 pceA transcripts per cell) but not with alternative substrates (<1 pceA transcript per cell). Cultures initially tfansferred or subcultivated on TCE showed very similar isotope fractionation, both for carbon (ecarbon: -8.6 parts per thousand +/- 0.3 parts per thousand or -8.8 parts per thousand +/- 0.2 parts per thousand) and chlorine (edilothie: 2.7%0 0.3 parts per thousand) with little variation (0.7 parts per thousand) for the different experimental conditions. Thus, TCE isotope fractionation by D. hafniense strain YS1 was affected by neither growth phase, pceA transcription, or translation, nor by PceA content per cell, suggesting that transport limitations did not affect isotope fractionation. Previously reported variable e values for other organohalide-respiring bacteria might thus be attributed to different expression levels of their multiple reductive dehalogenases.