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Appl. Environ. Microbiol. doi:10.1128/AEM.02834-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Diversity and mechanisms of alkali tolerance in lactobacilli

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

^* To whom correspondence should be addressed. Email: yokota{at}chem.agr.hokudai.ac.jp.

	Abstract

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