Escherichia coli

One property of this bacterium is its ability to grow in the absence of oxygen. This anaerobic growth is facilitated by the synthesis of enzymes which allow E. coli to use alternative compounds as electron acceptors. A number of these enzymes contain a complex metal cofactor, often the molybdopterin guanine dinucleotide (MGD) cofactor. Synthesis of this cofactor requires a number of steps, the last of which is incorporation the the nucleotide component . The proteins which catalyse this reaction are encoded by the mobAB locus which is being studies in Tracy Palmer's group.

Additionally, many of the MGD-containing reductases which are synthesised during anaerobic growth are located in the periplasmic space of E. coli. This poses an unique problem as there is convincing evidence that the large MGD cofactor is added to the partially folded apoprotein before it is transported to the periplasm. How is this large complex then translocated across the cytoplasmic membrane? The discovery of the mtt (or tat) genes which are essential for translocating these proteins to the periplasm has been a major breakthrough in this field. The role of the tat gene products in this novel process is also being studied in Tracy Palmer's lab.

While E. coli changes its respiratory pathways to grow anaerobically, it also changes some stages of central metabolism. The most important of these is the fate of pyruvate. During anaerobic growth, pyruvate is cleaved into formate and acetyl-CoA by the enzyme pyruvate formate lyase (PFL). Formate is subsequently used as a major electron donor during anaerobic respiration. PFL uses a radical mechanism for non-oxidatively cleaving pyruvate which seems to also be used by a number of other proteins in E. coli.

Another interesting feature of E. coli is that it can synthesise all its own amino acids, purines and pyrimidines using the nitrogen donor molecules glutamate and glutamine. The source of nitrogen for both these molecules is ammonium which E. coli preferentially uses as a nitrogen source. The transport of this key metabolite across the cytoplasmic membrane is being investigated in the lab of Mike Merrick.

A number of other aspects of E.coli biology are being studied in other laboratories on the Norwich Research Park. For details see the Microbes in Norwich web site.