Submitted to: American Dairy Science Association Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 3/1/2011
Publication Date: N/A
Technical Abstract: GABA (gamma-aminobutyric acid) is generated from glutamate by the action of glutamic acid decarboxylase (GAD) and characterized by hypotensive, diuretic and tranquilizing effects in humans and animals. The production of GABA by lactic acid starter bacteria would enhance the functionality of fermented dairy foods including cheeses and yogurt. The survey of 42 strains of the yogurt starter culture Streptococcus thermophilus by PCR techniques indicated the presence of a glutamate decarboxylase gene (gad) in 15 strains. DNA sequencing data indicated that in the genome of GAD+ S. thermophilus strains the gad as a rule is flanked by a transposase (5’) and a HD-superfamily hydrolase gene (3’). Specific primers were designed to amplify a 1.75-kb genomic fragment in S. thermophilus to include gad and its putative promoter region. The resulting PCR product was inserted into the 5.48-kb pMEU5a shuttle vector which was used to transform Escherichia coli DH5a. Subsequently, the recombinant plasmid pMEU5a-1/gad (7.24 kb) was transferred by electroporation into the GAD-negative strain S. thermophilus ST128. The ST128 transformants carrying the plasmid-encoded gad produced fully functional GAD enzyme as evidenced by the conversion of glutamate to GABA at a rate similar to strains with gad located on the chromosome. The results demonstrated the potential to equip non-GABA producing strains S. thermophilus and possibly other lactic acid bacteria with the capacity to produce GAD to improve culture performance in the development of functional foods.