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Journal of Bacteriology, February 2000, p. 898-904, Vol. 182, No. 4
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Function of a Principal Na+/H+ Antiporter, ShaA, Is Required for Initiation of Sporulation in Bacillus subtilis

Saori Kosono,1,* Yoshiaki Ohashi,2,dagger Fujio Kawamura,2 Makio Kitada,1 and Toshiaki Kudo1

Microbiology Laboratory, Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-0198,1 and Laboratory of Molecular Genetics, College of Science, Rikkyo (St. Paul's) University, Toshima-ku, Tokyo 171-8501,2 Japan

Received 19 August 1999/Accepted 30 November 1999

ShaA (sodium/hydrogen antiporter, previously termed YufT [or NtrA]), which is responsible for Na+/H+ antiporter activity, is considered to be the major Na+ excretion system in Bacillus subtilis. We found that a shaA-disrupted mutant of B. subtilis shows impaired sporulation but normal vegetative growth when the external Na+ concentration was increased in a low range. In the shaA mutant, sigma H-dependent expression of spo0A (PS) and spoVG at an early stage of sporulation was sensitive to external NaCl. The level of sigma H protein was reduced by the addition of NaCl, while the expression of spo0H, which encodes sigma H, was little affected, indicating that posttranscriptional control of sigma H rather than spo0H transcription is affected by the addition of NaCl in the shaA mutant. Since this mutant is considered to have a diminished ability to maintain a low internal Na+ concentration, an increased level of internal Na+ may affect posttranscriptional control of sigma H. Bypassing the phosphorelay by introducing the sof-1 mutation into this mutant did not restore spo0A (PS) expression, suggesting that disruption of shaA affects sigma H accumulation, but does not interfere with the phosphorylation and phosphotransfer reactions of the phosphorelay. These results suggest that ShaA plays a significant role at an early stage of sporulation and not only during vegetative growth. Our findings raise the possibility that fine control of cytoplasmic ion levels, including control of the internal Na+ concentration, may be important for the progression of the sporulation process.

* Corresponding author. Mailing address: Microbiology Laboratory, Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama 351-0198, Japan. Phone: 81-48-467-9545. Fax: 81-48-462-4672. E-mail: kosono{at}postman.riken.go.jp.

dagger Present address: National Food Research Institute, Tsukuba, Ibaraki 305-8642, Japan.

Journal of Bacteriology, February 2000, p. 898-904, Vol. 182, No. 4
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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