Identification of HtrII as a Chemotransducer in the Arachaeon Halobacterium salinarum using a Newly Developed Agarose-in-Plug Bridge Assay

Yu, Hyung
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University of Hawaii at Manoa
Signal transduction in the archaeon Halobacterium salinarum is mediated by thirteen soluble and membrane-bound transducers. Phototaxis in H. salinarum is processed via two signaling complexes: sensory rhodopsin I photoreceptor-Htrl phototransducer (SRI­ Htrl) and sensory rhodopsin II photoreceptor-Htrll phototransducer (SRll-Htrll). Unlike the Htrl phototransducer, the Htrll phototransducer contains a large periplasmic domain-a classic feature of bacterial chemotransducers. Thus the existence of a periplasmic domain in the Htrll phototransducer suggests that Htrll is not only involved in phototaxis, but also in chemotaxis. To test this hypothesis, we developed an agarose-in­ plug bridge assay to study chemotaxis in H. salinarum by detecting the density of cells around a solidified agarose plug containing chemoeffectors. The role of Htrll as a chemotransducer was studied by using this assay with overexpressed and deleted Htrll strains to all essential amino acids. The deleted Htrll strain showed little chemotactic response to the agarose plug containing 10 mM L-serine compared to the overexpressed Htrll strain. Htrll is the first example of a transducer involved in both phototaxis and chemotaxis.
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