Question

What phenotypes would you predict for a bacterium with a mutation in cheA (kinase)? Explain the reasons for the expected phenotypes such as presence of chemotactic​ reactions, motility, or movement such as swimming, tumbling or both.

Answer 1

cheA (kinase) is an autophosphorylating histidine kinase protein generally found in bacteria. Its activity is regulated by transducer or receptor proteins. It plays a central role in the regulation of metabolic responses and chemotaxis. The expected phenotypes are observed because of the mutation. CheA plays a central signalling role in bacterial chemotaxis pathways. For instance, in E. coli cheA forms signalling complexes with five membrane associated chemoreceptors. These are known as methyl accepting chemotaxis proteins (MCPs). These MCPs interacts with flagellar motors by controlling cheA activity. At a histidine residue cheA gets autophosphorylated using ATP as phophodonor. It subsequently donates the phosphoryl groups to two response regulators, cheY and cheB. The phosphorylated cheY, also known as phospho-cheY, interacts with switching machinery present at the base of flagellar motors. It promotes clockwise rotation. This in turn causes random turning episodes or the tumbles observed during swimming. Now, the phospho-cheB functions in a feedback loop. The feedback circuit helps the cells ti detect temporal changes in attractant and repellent concentrations as they move through spatial concentration gradients.