Background Research

Bacteria used for research

Bacteria Shewanella are extensively used in research because of their unique metabolic characteristics. They are facultative anaerobes that can reduce insoluble Mn+4 and Fe+3 oxides if they are in need of a final electron acceptor. When fumarate is added to growth media under anaerobic conditions, a periplasmic flavocytochrome c3 is made that catalyzes the reduction of fumarate to succinate. This is exactly the reverse reaction to that catalyzed by SDH. Fumarate is a favorable electron acceptor because it is easily synthesized in the organism and has an appropriate redox potential (Leys et al 1999).

Figure 7. Bacteria similar in shape and growth pattern to Shewella (ARS Image Gallery, Image Number K7970-4)

Shewanella Flavocytochrome 3 Facts

The flavocytochrome was studied because it is both a single polypeptide chain and soluble, which makes it easier to work with than SDH. It is considered a tetraheme Fcc3 because it contains four covalently bound heme groups at the N-terminal cytochrome domain. Although this enzyme shows little three-dimensional similarity to other cytochromes, the sequence of the FAD binding domain is similar to membrane-bound flavoproteins (SDH and fumarate reductase). The majority of the work accomplished by the flavocytochrome occurs in the FAD binding domain. FAD accepts and donates electrons to bound substrates (Taylor et al 1999).