Essential role of the cytoplasmic chemoreceptor TlpT in the de novo formation of chemosensory complexes in Rhodobacter sphaeroides.
Jones CW., Armitage JP.
Bacterial chemosensory proteins form large hexagonal arrays. Several key feature of chemotactic signalling depend on these large arrays, namely cooperativity between receptors, sensitivity, integration of different signals and adaptation. The best studied arrays are the membrane associated arrays found in most bacteria. Rhodobacter sphaeroides has two spatially distinct chemosensory arrays, one transmembrane and the other cytoplasmic. These two arrays work together to control a single flagellum. Deletion of one of the soluble chemoreceptors, TlpT, results in the loss of formation of the cytoplasmic array. Here we show the expression of TlpT in a tlpT deletion background results in the reformation of the cytoplasmic array. The number of arrays formed is dependent on the cell length, indicating spatial limitations on the number of arrays in a cell, and stochastic assembly. Deletion of PpfA, a protein required for the positioning and segregation on the cytoplasmic array, results in slower array formation upon TlpT expression and fewer arrays, suggesting it accelerates cluster assembly.Importance Bacterial chemosensory arrays are usually membrane associated and consist of thousands of copies of receptors, adaptor proteins, kinases and adaptation enzymes packed into large hexagonal structures. Rhodobacter sphaeroides also has cytoplasmic arrays, which divide and segregate using a chromosome associated ATPase PpfA. Expression of the soluble chemoreceptor TlpT is shown to drive the formation of the arrays, accelerated by PpfA. The positioning of these de novo arrays suggests their position is the result of stochastic assembly, rather than active positioning.