The gut bacterium Escherichia coli has, for a variety of reasons, become a model organism for studying many of life's essential processes. Due to its rapid growth rate, simple nutritional requirements, well established genetics and completed genomes sequence, more is now known about E. coli than any other living organism.
The preferred source of nitrogen for E. coli, as for many bacteria, is ammonium from which the primary nitrogen donor molecules glutamate and glutamine are synthesised. The movement of ammonium into the cell across the cytoplasmic membrane is consequently a key process in nitrogen metabolism and this is achieved by the ammonium transport (Amt) proteins. Amt proteins are found in virtually all living organisms and in the lab of Prof. Mike Merrick the E. coli AmtB protein has been developed as a model system to gain insight into this fundamental biological process.
E. coli, like many enteric bacteria, is able to couple periplasmic nitrate ammonification to energy conserving electron transport in order to colonise anaerobic environments. Nitrate ammonification occurs in two steps catalysed by two distinct classes of enzyme. Nitrate reductases reduce nitrate to nitrite while nitrite reductase reduces nitrite to ammonium and homologs of these enzymes are found in a wide range of proteobacteria with medical, environmental and biotechnological importance. In addition to the cellular significance of nitrate ammonification, the mechanism by which nitrite is reduced to ammonium by a single enzyme is of considerable interest since it occurs without the release of intermediates such as nitric oxide or nitrous oxide that may be harmful to the atmosphere. Prof. David Richardson, Dr Tom Clarke, Dr Andrew Hemmings, Dr Myles Cheesman and Prof. Julea Butt study cellular, structural and biochemical aspects of nitrate ammonification in E. coli. This has informed not only the mechanisms for processing nitrate and nitrite but also those for handling the widely encountered cytotoxins nitric oxide and sulphite.
E.coli is the model organism of choice for investigations of many fundamental biological processes and another such example is in the study of DNA topoisomerases. These are a vitally important class of proteins involved in the control of the topological state of DNA and their major biological functions are in DNA replication, recombination and the control of gene expression. One of the best characterised DNA topoisomerases is DNA gyrase from E. coli which is studied by Prof. Tony Maxwell. E. coli is also being used to investigate genome stability by Dr. Richard Bowater. The role of long triplet repeats in DNA stability is being investigated along with the biochemical mechanisms which generate these instabilities.