Analysis of linear respiratory chain mutant strains of
Escherichia coli.
Stelder, S.K., Nouse, N., Ter Beek, A.S., Teixeira de Mattos, M.J.
Molecular Microbial Physiology Group, Swammerdam Institute for Life Sciences, University of Amsterdam
Three mutants have successfully been created and have been used in growth experiments to
determine why the respiratory chain of Escherichia coli is branched. The growth rates as well
as which fermentation products are formed have been determined under aerobic conditions at
acidic pH 5.5, optimal pH 6.9 and basic pH 7.9. The mutants are a Cyt bd-II mutant
(∆cydB∆nuoB∆cyoB::kan) with a linear respiratory chain through Cytochrome bd-II, a Cyt bo
mutant (∆cydB∆nuoB∆appB::kan) with a linear respiratory chain through Cytochrome bo and
an fnr arcA mutant (∆fnr∆arcA) which lacks the regulatory proteins of the FNR and ArcAB
system required for transcriptional control of the complexes involved in the respiratory chain
under an- & microaerboic conditions. Several distinguishing characteristics have been
determined for each mutant. For instance the Cyt bd-II mutant grows much slower than the
wild type and is incapable of growth at pH 5.5, it also produces lactate in addition to a larger
acetate production indicating serious problems concerning its ATP production. The Cyt bo
mutant grows at the same rate as the wild type except at pH 7.9 when it appears to grow
slower and has a prolonged lag phase. The fnr arcA mutant shows little or no difference
compared to the wild type as is expected under aerobic conditions when these regulators are
normally not active. The results provide a clue to which cytochrome is used at which pH and
provide the answer that the respiratory chain is branched in order to be able to respond to
changes in the pH of the cells environment. More specifically Cyt bo is responsible for most
of the cells proton translocation in the respiratory chain at pH 5.5 and 6.9 under aerobic
conditions and Cyt bd-II appears not functional at pH 5.5. However, development of a third
linear respiratory chain mutant and a repeat of the experiments in chemostat cultures are
required to confirm this.