Phototaxis Chemotaxiss

Cercignani G, Lucia S, Petracchi D (1998) Motility, chemotaxis and phototaxis measurements by image analysis. In Wilkinson MHF, Schut F (eds) Digital Image Analysis of Microbes. Wiley, New York, p 343... 

Phototaxis in Rb. sphaeroides is triggered by the effects of the photosynthetic machinery on the rate of electron transfer (9). Thus, in contrast to the situation in H. salinarum, phototaxis in Rb. sphaeroides does not involve a dedicated photosensor. The rate of electron transfer is presumably sensed by an as yet unidentified receptor, and relayed into the complex set of Che proteins in Rb. sphaeroides (Fig. 1). Thus, phototaxis responses in Rb. sphaeroides can be regarded as a form of redox taxis and are modulated by factors affecting electron transport, such as the presence or absence of oxygen (19). The Rb. sphaeroides encodes nine transmembrane chemoreceptors (MCPs) and four putative cytoplasmic MCPs, four CheA proteins, and six CheY proteins (20). A number of proteins from this Che system have been shown to be required for phototaxis in Rb. sphaeroides, showing that the signal transduction chains for phototaxis and chemotaxis converge at this level (21). A similar situation holds for phototaxis and chemotaxis in R. centenum (see later). 

Rudolph, J. and Oesterhelt, D. (1995). Chemotaxis and phototaxis require a CheA histidine kinase in the archaeon Halohacterium salinarium. EMBO J. 14, 667-673. 

HtrII (1-159) under consideration consists of the C-terminal residue protruding from the cytoplasmic membrane surface (82-159) mainly as linker (Fig. 34) that may participate in the coiled-coil form responsible for phototaxis besides the two transmembrane a-helices. by analogy with the X-ray diffraction picture of four-helical-bundle structure of the cytoplasmic domain of a serine chemotaxis receptor. Indeed, each monomer is a 70 turn a-helix folded back on itself to form two long antiparallel coiled-coil structures. 

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