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Functional Characterization and Mutagenesis of the Proposed Behavioral Sensor TlpD of Helicobacter pylori

Tobias Schweinitzer,^1, Tomoko Mizote,^2, Naohiro Ishikawa,² Alexey Dudnik,¹ Sakiko Inatsu,² Sören Schreiber,³ Sebastian Suerbaum,¹ Shin-Ichi Aizawa,⁴ and Christine Josenhans^1*,

Institute for Medical Microbiology, Hannover Medical School, 30625 Hannover, Germany,¹ Department of Physiology, Ruhr-University Bochum, 44780 Bochum, Germany,³ Department of Human Science, Yamaguchi Prefectural University, Yamaguchi 753-8502, Japan,² Department of Life Sciences, Prefectural University of Hiroshima, Shobara 727-0023, Japan⁴

Received 13 December 2007/ Accepted 23 January 2008

Helicobacter pylori requires flagellar motility and chemotaxis to establish and maintain chronic infection of the human stomach. The pH gradient in the stomach mucus is essential for bacterial orientation and guides the bacterium toward a narrow layer of the mucus, suggesting that H. pylori is capable of energy sensing or taxis. In the present study, H. pylori wild-type behavior in a temporal swimming assay could be altered by electron transport inhibitors, indicating that a connection between metabolism and behavior exists. In order to elucidate mechanisms of behavioral responses of H. pylori related to energy sensing, we investigated the phenotypes of single and multiple mutants of the four proposed chemotaxis sensor proteins. All sensor mutants were motile, but they diverged in their behavior in media supporting different energy yields. One proposed intracellular sensor, TlpD, was crucial for behavioral responses of H. pylori in defined media which did not permit growth and led to reduced bacterial energy levels. Suboptimal energetic conditions and inhibition of electron transport induced an increased frequency of stops and direction changes in the wild type but not in tlpD mutants. Loss of metabolism-dependent behavior in tlpD mutants could be reversed by complementation but not by electron donors bypassing the activity of the electron transport chain, in contrast to the case for the wild type. TlpD, which apparently lacks transmembrane domains, was detected both in the bacterial cytoplasm and at the bacterial periphery. The proposed energy sensor TlpD was found to mediate a repellent tactic response away from conditions of reduced electron transport.

Published ahead of print on 1 February 2008.

T.S. and T.M. share first authorship; T.M., T.S., and C.J. contributed equally to this study.

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