Some Important Concepts about Microorganisms

The H2 produced by this second bacterium is subsequently used by the first microorganism, as well as by organisms that use it to make methane from C02. Finally, another species utilizes the acetate and releases methane  

Second, organisms may invest metabolic energy to synthesize reactive species. For example, before it is used to oxidize hydrocarbons, 02 is converted to a much more reactive oxidant by complexation and reducing it with a compound the organisms had to spend energy to make (see Section 17.3). This scheme is similar to one previously discussed in photochemical transformations where, by absorption of light, activated species are formed that are much more reactive (Chapter 16). 

This imperfect binding specificity principle also helps us to understand why chemicals called competitive inhibitors may block the active sites of enzymes. These inhibitors are structurally like the enzyme s appropriate substrate, enabling them to bind. But these compounds may be somewhat, or even completely, unreactive. Such enzyme inhibition appears to explain the limited microbial dehalogenation of 3-chlorobenzoate in the presence of 3,5-dichlorobenzoate (Suflita et al., 1983). In this case, 3,5-dichlorobenzoate is initially transformed to 3-chlorobenzoate  

Subsequent degradation of the 3-chlorobenzoate does not proceed until most of the 3,5-dichlorobenzoate is transformed. The explanation for this finding is that the dichloro aromatic substrate competes with the monochloro compound for the same enzyme active site. As a result, 3,5-dichlorobenzoate acts as a competitive inhibitor of the biochemical removal of 3-chlorobenzoate. Once nearly all the dichloro 

This type of substrate-substrate interaction may be especially important for contaminants introduced as mixtures in the environment. One example is the mix of polycyclic aromatic hydrocarbons co-introduced in oil spills or in coal tar wastes. Laboratory observations of the biodegradation of such hydrocarbons show that some of these components can inhibit the removal of other compounds in the mix (Guha et al., 1999). Such results indicate that the rate of a particular chemical s biotransformation may be a function of factors such as the presence of competing substrates interacting with the same enzyme systems. 

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