Nonconventional hydrolytic dehalogenation of 1-chlorobutane by dehydrated bacteria in a continuous solid-gas biofilter

Nonconventional hydrolytic dehalogenation of 1-chlorobutane by dehydrated bacteria in a continuous solid-gas biofilter
May 31, 2005
Benjamin Erable, Isabelle Goubet, Sylvain Lamare, Amira Seltana, Marie Dominique Legoy, Thierry Maugard *
Laboratoire de Biotechnologies et de Chimie Bio-organique CNRS FRE 2766, B?timent Marie Curie, Universit? de La Rochelle, Avenue Michel Cr?peau, 17042 La Rochelle cedex 1, France; telephone: + 33 5 4645 82 77; fax: + 33 5 4645 8265
Biotechnology and Bioengineering
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Abstract
Rhodococcus erythropolis NCIMB 13064 and Xanthobacter autotrophicus GJ10 are able to catalyze the conversion of halogenated hydrocarbons to their corresponding alcohols. These strains are attractive biocatalysts for gas phase remediation of polluted gaseous effluents because of their complementary specificity for short or medium and for mono-, di-, or trisubstituted halogenated hydrocarbons (C2-C8 for Rhodococcus erythropolis and C1-C4 for Xanthobacter autotrophicus).
After dehydration, these bacteria can catalyze the hydrolytic dehalogenation of 1-chlorobutane in a nonconventional gas phase system under a controlled water thermodynamic activity (aw). This process makes it possible to avoid the problems of solubility and bacterial development due to the presence of water in the traditional biofilters.
In the aqueous phase, the dehalogenase activity of Rhodococcus erythropolis is less sensitive to thermal denaturation and the apparent Michaelis-Menten constants at 30?C were 0.4 mM and 2.40 mol min-1 g-1 for Km and Vmax, respectively. For Xanthobacter autotrophicus they were 2.8 mM and 0.35 mol min-1 g-1.
In the gas phase, the behavior of dehydrated Xanthobacter autotrophicus cells is different from that observed with Rhododcoccus erythropolis cells. The stability of the dehalogenase activity is markedly lower. It is shown that the HCl produced during the reaction is responsible for this low stability. Contrary to Rhodococcus erythropolis cells, disruption of cell walls does not increase the stability of the dehalogenase activity.
The activity and stability of lyophilized Xanthobacter autotrophicus GJ10 cells are dependant on various parameters. Optimal dehalogenase activity was determined for water thermodynamic activity (aw) of 0.85. A temperature of 30?C offers the best compromise between activity and stability. The pH control before dehydration plays a role in the ionization state of the dehalogenase in the cells. The apparent Michaelis-Menten constants Km and Vmax for the dehydrated Xanthobacter autotrophicus cells were 0.07 (1-chlorobutane thermodynamic activity) and 0.08 mol min-1 g-1 of cells, respectively.
A maximal transformation capacity of 1.4 g of 1-chlorobutane per day was finally obtained using 1g of lyophilized Xanthobacter autotrophicus GJ10 cells. ? 2005 Wiley Periodicals, Inc.