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Applied and Environmental Microbiology, April 2009, p. 2406-2413, Vol. 75, No. 8
0099-2240/09/$08.00+0     doi:10.1128/AEM.02387-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Stimulation of Expression of a Silica-Induced Protein (Sip) in Thermus thermophilus by Supersaturated Silicic Acid{triangledown}

Katsumi Doi,1* Yasuhiro Fujino,1 Fumio Inagaki,1 Ryouichi Kawatsu,1 Miki Tahara,1 Toshihisa Ohshima,1 Yoshihiro Okaue,2 Takushi Yokoyama,2 Satoru Iwai,3 and Seiya Ogata3

Department of Genetic Resources Technology, Faculty of Agriculture,1 Department of Chemistry, Faculty of Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan,2 Department of Applied Microbial Technology, Faculty of Bioscience, Sojo University, 4-22-1 Ikeda, Kumamoto 860-0082, Japan3

Received 16 October 2008/ Accepted 9 February 2009

The effects of silicic acid on the growth of Thermus thermophilus TMY, an extreme thermophile isolated from a siliceous deposit formed from geothermal water at a geothermal power plant in Japan, were examined at 75°C. At concentrations higher than the solubility of amorphous silica (400 to 700 ppm SiO2), a silica-induced protein (Sip) was isolated from the cell envelope fraction of log-phase TMY cells grown in the presence of supersaturated silicic acid. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed the molecular mass and pI of Sip to be about 35 kDa and 9.5, respectively. Induction of Sip expression occurred within 1 h after the addition of a supersaturating concentration of silicic acid to TM broth. Expression of Sip-like proteins was also observed in other thermophiles, including T. thermophilus HB8 and Thermus aquaticus YT-1. The amino acid sequence of Sip was similar to that of the predicted solute-binding protein of the Fe3+ ABC transporter in T. thermophilus HB8 (locus tag, TTHA1628; GenBank accession no. NC_006461; GeneID, 3169376). The sip gene (987-bp) product showed 87% identity with the TTHA1628 product and the presumed Fe3+-binding protein of T. thermophilus HB27 (locus tag TTC1264; GenBank accession no. NC_005835; GeneID, 2774619). Within the genome, sip is situated as a component of the Fbp-type ABC transporter operon, which contains a palindromic structure immediately downstream of sip. This structure is conserved in other T. thermophilus genomes and may function as a terminator that causes definitive Sip expression in response to silica stress.

* Corresponding author. Mailing address: Department of Genetic Resources Technology, Faculty of Agriculture, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan. Phone and fax: 81 (0)92 642 3059. E-mail: doi{at}agr.kyushu-u.ac.jp

{triangledown} Published ahead of print on 20 February 2009.

Applied and Environmental Microbiology, April 2009, p. 2406-2413, Vol. 75, No. 8
0099-2240/09/$08.00+0     doi:10.1128/AEM.02387-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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