Abstract
Organohalide-respiring Desulfitobacterium strains are believed to play an important role in the bioremediation and natural attenuation of chlorinated aliphatic and aromatic hydrocarbons. However, several studies have reported that chloroform significantly inhibits microbial reductive dechlorination of chloroethene. In this study, we examined the effect of chloroform on several Desulfitobacterium strains, including ortho-chlorophenol-dechlorinating Desulfitobacterium dehalogenans JW/IU-1 and Desulfitobacterium hafniense DCB-2, and also the chloroethene-dechlorinating strain D. hafniense TCE1. In medium containing 3-chloro-4-hydroxyphenylacetate as an electron acceptor, chloroform inhibited the growth of strains JW/IU-1 and DCB-2. Although chloroform did not directly inhibit dechlorination of 3-chloro-4-hydroxyphenylacetate by resting cells, cells cultivated with chloroform showed decreased dechlorination activity. Moreover, transcription of the gene encoding the reductive dehalogenase CprA decreased significantly in cells cultivated with chloroform. These results indicate that chloroform inhibits the growth and dechlorination activity of strains JW/IU-1 and DCB-2 via inhibition of cprA transcription. In contrast, cultivation of strain TCE1 in the presence of chloroform gave rise to a PceA reductive dehalogenase gene-deletion variant of strain TCE1; a similar phenomenon was observed in our previous study of chloroethene-dechlorinating D. hafniense strain Y51. Our results suggest that chloroform extensively inhibits the dechlorination activity of Desulfitobacterium strains, and that the inhibitory mechanism appears to differ between ortho-chlorophenol dechlorinators and chloroethene dechlorinators.
Highlights
Organohalide respiration is an anaerobic process in which a halogenated organic compound serves as the electron acceptor
Effect of CF on the growth of D. dehalogenans strain JW/ IU-1 and D. hafniense strain DCB-2 To evaluate the inhibitory effect of CF on the growth of strains JW/IU-1 and DCB-2, we examined growth curves for cells cultured with and without CF at a concentration of 1, 10, and 100 μM in medium containing fumarate or 3-Cl-4-OHPA as the electron acceptor (Figure 1)
Because 100 μM CF significantly inhibited the growth rate of strain JW/IU-1 and caused the extended lag phase and the reduced cell yield of strain DCB-2 in medium containing 3-Cl-4-OHPA (Figure 1), we investigated the effect of CF on dechlorination of 3-Cl-4-OHPA by resting cells prepared from strains JW/IU-1 and DCB-2 cultivated with or without 100 μM CF (Figure 2)
Summary
Organohalide respiration is an anaerobic process in which a halogenated organic compound serves as the electron acceptor. Various organohalide-respiring bacteria (OHRB) have been applied to the bioremediation of toxic chlorinated hydrocarbons in anaerobic environments (Smidt and de Vos 2004; Löffler and Edwards 2006; Maphosa et al 2010). In this process, organohalides are reductively dehalogenated. Desulfitobacterium hafniense strain DCB-2 and Desulfitobacterium dehalogenans strain JW/IU-1 respire with ortho-chlorophenols such as 3-chloro-4hydroxyphenylacete (3-Cl-4-OHPA), whereas D. hafniense strains TCE1 and Y51 respire with PCE and TCE (Madsen and Licht 1992; Utkin et al 1994; Gerritse et al 1999; Suyama et al 2001)
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