For such a link to be established, the electron transport components must be localized in the
outer membrane of the bacterial cells (in the case of gram-negative bacteria), where they can
make direct contact with either the azo dye substrate or a redox mediator at the cell surface
(Myers and Myers,1992). In addition, Gingell and Walker have shown that low molecular
weight redox mediator compounds can act as electron shuttles between the azo dye and an
NADH (nicotinamide adenine dinucleotide)-dependent azo reductase that is situated in the
outer membrane.