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Applied and Environmental Microbiology, June 2007, p. 3909-3915, Vol. 73, No. 12
0099-2240/07/$08.00+0     doi:10.1128/AEM.02834-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Diversity and Mechanisms of Alkali Tolerance in Lactobacilli{triangledown}

Yuki Sawatari and Atsushi Yokota*

Laboratory of Microbial Physiology, Research Faculty of Agriculture, Hokkaido University, Kita 9 Nishi 9, Kita-ku, Sapporo, Hokkaido 060-8589, Japan

Received 6 December 2006/ Accepted 8 April 2007

We determined the maximum pH that allows growth (pHmax) for 34 strains of lactobacilli. High alkali tolerance was exhibited by strains of Lactobacillus casei, L. paracasei subsp. tolerans, L. paracasei subsp. paracasei, L. curvatus, L. pentosus, and L. plantarum that originated from plant material, with pHmax values between 8.5 and 8.9. Among these, L. casei NRIC 1917 and L. paracasei subsp. tolerans NRIC 1940 showed the highest pHmax, at 8.9. Digestive tract isolates of L. gasseri, L. johnsonii, L. reuteri, L. salivarius subsp. salicinius, and L. salivarius subsp. salivarius exhibited moderate alkali tolerance, with pHmax values between 8.1 and 8.5. Dairy isolates of L. delbrueckii subsp. bulgaricus, L. delbrueckii subsp. lactis, and L. helveticus exhibited no alkali tolerance, with pHmax values between 6.7 and 7.1. Measurement of the internal pH of representative strains revealed the formation of transmembrane proton gradients ({Delta}pH) in a reversed direction (i.e., acidic interior) at alkaline external-pH ranges, regardless of their degrees of alkali tolerance. Thus, the reversed {Delta}pH did not determine alkali tolerance diversity. However, the {Delta}pH contributed to alkali tolerance, as the pHmax values of several strains decreased with the addition of nigericin, which dissipates {Delta}pH. Although neutral external-pH values resulted in the highest glycolysis activity in the presence of nigericin regardless of alkali tolerance, substantial glucose utilization was still detected in the alkali-tolerant strains, even in a pH range of between 8.0 and 8.5, at which the remaining strains lost most activity. Therefore, the alkali tolerance of glycolysis reactions contributes greatly to the determination of alkali tolerance diversity.

* Corresponding author. Mailing address: Laboratory of Microbial Physiology, Division of Applied Bioscience, Research Faculty of Agriculture, Hokkaido University, Kita 9 Nishi 9, Kita-ku, Sapporo, Hokkaido 060-8589, Japan. Phone: 81-11-706-2501. Fax: 81-11-706-4961. E-mail: yokota{at}chem.agr.hokudai.ac.jp

{triangledown} Published ahead of print on 20 April 2007.

Applied and Environmental Microbiology, June 2007, p. 3909-3915, Vol. 73, No. 12
0099-2240/07/$08.00+0     doi:10.1128/AEM.02834-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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