Aerobic Cometabolism of Chlorinated Aliphatic Hydrocarbons by Toluene-Oxidizing Bacteria: Physiological
Consequences and Adaptive Responses
Goal
The objectives of this study are to systematically characterize the toxicity and energy costs associated with chlorinated aliphatic
hydrocarbon (CAH) cometabolism in B. cepacia G4 and other representative toluene-oxidizing bacteria, and to identify cellular mechanisms
and growth conditions that minimize these deleterious effects.
Rationale
From the biological standpoint, degradation of CAHs by aerobic cometabolism is largely dependent on two factors: 1) cellular
energy requirements and 2) the toxicity often associated with CAH oxidation. Data from previous studies have implied that loss of oxygenase
activity, cell viability, or reductant stores may ultimately limit the capacity of individual bacterial strains or consortia to oxidize CAHs.
However, the extent that these or other factors interact to limit CAH cometabolism at the cellular level is largely unknown. Furthermore,
cellular factors that ultimately limit CAH oxidation have rarely been compared among different bacteria. Certainly, it is not known what
physiological or genetic determinants distinguish the proficient CAH-degrading strains. By identifying the common biochemical and molecular
mechanisms that limit CAH cometabolism, better control and application of this important degradative process should be realized.
Approach
The effects of CAH cometabolism at the cellular level will first be examined in B. cepacia G4. The effects of short-term
incubations with trichloroethylene (TCE), 1,1-dichloroethylene (1,1-DCE), and ethylene on cell viability, oxygenase activity, and cellular
energy reserves will be assessed in G4. Growth conditions that limit toxicity or energy depletion in G4, thus maximizing its TCE-degrading
potential, will also be investigated. In addition, the pattern of gene or protein expression in B. cepacia G4 cells exposed to TCE, 1,1-DCE,
ethylene, and other general environmental stresses will be analyzed. Using the results obtained with G4 as a framework, the factors that limit
CAH cometabolism by other toluene-oxidizing bacteria will be investigated.
Status
The effects of TCE cometabolism on resting cell suspensions of B. cepacia G4 have been examined. A slow loss of toluene
2-monooxygenase activity is observed upon TCE degradation; however, the cells exhibit an exponential loss of viability, as determined by LB
plate counts. Neither oxygenase activity nor cell viability is lost upon ethylene consumption. Preliminary evidence suggests that many B.
cepacia G4 cells are sub-lethally injured while degrading TCE, and can eventually divide if incubated under suitable conditions. Also, it
appears that B. cepacia G4 suffers DNA damage during TCE cometabolism.
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Last modified on: March 16, 2000.
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