POSTERS - BLAST X - University of Utah

BLAST X Poster #31
THERMOSENSING FUNCTION OF Aer, A REDOX SENSOR OF E. COLI
So-ichiro Nishiyama 1 , Shinji Ohno 2 , Noriko Ohta 3 , Akihiko Ishijima 4 1, 5
and Ikuro Kawagishi
1
Department of Frontier Bioscience, Faculty of Bioscience and Applied Chemistry, Hosei
University
2
Department of Material Chemistry, Faculty of Engineering, Hosei University
3
Division of Biological Science, Graduate School of Science, Nagoya University
4
Institute of Multidisciplinary, Research for Advanced Materials, Tohoku University
5
Department of Frontier Bioscience, Faculty of Engineering, Hosei University
Some motile bacteria can sense temperature and move to temperatures best-suited to
growth. This behavior, called thermotaxis, has been extensively studied in Escherichia coli.
Our early studies revealed that E. coli thermotaxis is mediated by chemoreceptors that also
sense amino acids or sugars: Tsr (serine), Tar (aspartate and maltose) and Trg (ribose and
galactose) function as warm sensors, producing counter-clockwise or clockwise flagellar rotation
signals upon temperature upshift and downshift, respectively. Tap (dipeptides, pyrimidines)
functions as a cold sensor, producing CW and CCW signals upon temperature increases and
decreases, respectively. Unique among these temperature sensors, Tar switches from a warm
sensor to a cold sensor after adaptation to its ligand, aspartate. Intensive studies of Tar
revealed that the receptor’s transmembrane and methylation domains play important roles in
thermotactic responses, but what part of the chemoreceptor molecule actually senses
temperature, remains unknown.
In this study, we found that the aerotaxis transducer Aer also has temperature-sensing
ability. An otherwise receptor-less strain expressing only aer showed extremely smooth
swimming and did not show any thermoresponse. However, after imposing a CW rotational
bias by adding the general repellent, glycerol (up to 10% w/v) or by co-expressing a cytoplasmic
fragment of Tar that does not mediate a thermoresponse, the cells showed CCW and CW
responses to temperature upshifts and downshifts, respectively. These results suggest that Aer
functions as a warm sensor, even though, unlike the Tar, Tap, Tsr, and Trg chemoreceptors,
Aer does not have a periplasmic ligand-binding domain. Thus, temperature sensing by E. coli
chemoreceptors may be a general attribute of their highly-conserved cytoplasmic signaling
domain (or their less conserved transmembrane domain).
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