Dynamic localization of chemotaxis proteins in Bacillus subtilis

Understanding the subcellular localization of a protein or protein clusters is helpful to conceive the function of the proteins or the mechanism of the pathway involving these proteins. Bacteria, although small and single-celled, have been shown to have delicate subcellular locations for most of its components. The modified two-component chemotaxis system employed by bacteria has a core where the receptors form ternary complexes with CheA histidine kinases and CheW adaptor proteins. These complexes are arranged in semi-ordered arrays clustered predominantly at the cell poles. The prevailing models assume that these arrays are static and reorganize only locally in response to attractant binding. Recent studies have shown, however, that these structures are in fact much more fluid. Previous study on localization of the chemotaxis proteins is mostly in Escherichia coli, which is relatively simple in terms of chemotaxis proteins it has and the mechanism it utilizes. In contrast, the gram-positive soil bacterium Bacillus subtilis has at least one copy of all the chemotaxis proteins found up to now and represents a general model for chemotaxis in bacteria. In this work, we investigated the dynamic localization of the chemotaxis signaling arrays in B. subtilis using immunofluorescence. We found that the receptors were localized in clusters at the poles in most cells. However, when the cells were exposed to attractant, the number exhibiting polar clusters was reduced roughly two-fold whereas the number exhibiting lateral clusters distinct from the poles increased significantly. The redistribution of the receptors was reversible, as polar localization was reestablished in adapted cells. We also investigated the dynamic localization of CheV, a hybrid protein consisting of an N-terminal CheW-like adaptor domain and a C-terminal response regulator domain that is known to phosphorylated by CheA. Interestingly, we found that CheV was localized predominantly at lateral clusters in unstimulated cells. However, upon exposure to attractant, CheV transiently relocalized to the cell poles. Moreover, CheV relocalization was phosphorylation dependent. Collectively, these results demonstrate that the chemotaxis signaling arrays in B. subtilis are dynamic structures and that feedback loops involving phosphorylation may regulate the positioning of individual proteins