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Applied and Environmental Microbiology, September 2004, p. 5315-5322, Vol. 70, No. 9
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.9.5315-5322.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Identification and Inactivation of Genetic Loci Involved with Lactobacillus acidophilus Acid Tolerance

M. Andrea Azcarate-Peril,1 Eric Altermann,1 Rebecca L. Hoover-Fitzula,1 Raul J. Cano,2 and Todd R. Klaenhammer1*

Department of Food Science, North Carolina State University, Raleigh, North Carolina,1 Environmental Biotechnology Institute, California Polytechnic State University, San Luis Obispo, California2

Received 17 February 2004/ Accepted 14 May 2004

Amino acid decarboxylation-antiporter reactions are one of the most important systems for maintaining intracellular pH between physiological limits under acid stress. We analyzed the Lactobacillus acidophilus NCFM complete genome sequence and selected four open reading frames with similarities to genes involved with decarboxylation reactions involved in acid tolerance in several microorganisms. Putative genes encoding an ornithine decarboxylase, an amino acid permease, a glutamate {gamma}-aminobutyrate antiporter, and a transcriptional regulator were disrupted by insertional inactivation. The ability of L. acidophilus to survive low-pH conditions, such as those encountered in the stomach or fermented dairy foods, was investigated and compared to the abilities of early- and late-stationary-phase cells of the mutants by challenging them with a variety of acidic conditions. All of the integrants were more sensitive to low pH than the parental strain. Interestingly, each integrant also exhibited an adaptive acid response during logarithmic growth, indicating that multiple mechanisms are present and orchestrated in L. acidophilus in response to acid challenge.

* Corresponding author. Mailing address: Department of Food Science, North Carolina State University, Box 7624, Raleigh, NC 27695. Phone: (919) 515-2972. Fax: (919) 515-7124. E-mail: klaenhammer{at}ncsu.edu.

Applied and Environmental Microbiology, September 2004, p. 5315-5322, Vol. 70, No. 9
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.9.5315-5322.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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