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Applied and Environmental Microbiology, January 2005, p. 303-311, Vol. 71, No. 1
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.1.303-311.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Identification, Cloning, and Characterization of a Lactococcus lactis Branched-Chain {alpha}-Keto Acid Decarboxylase Involved in Flavor Formation

Bart A. Smit,1 Johan E. T. van Hylckama Vlieg,1 Wim J. M. Engels,1* Laura Meijer,1 Jan T. M. Wouters,2 and Gerrit Smit1,2

Department of Flavor, Nutrition and Ingredients, NIZO food research, Ede,1 Department of Agrotechnology and Food Sciences, Wageningen University, Wageningen, The Netherlands2

Received 8 February 2004/ Accepted 29 August 2004

The biochemical pathway for formation of branched-chain aldehydes, which are important flavor compounds derived from proteins in fermented dairy products, consists of a protease, peptidases, a transaminase, and a branched-chain {alpha}-keto acid decarboxylase (KdcA). The activity of the latter enzyme has been found only in a limited number of Lactococcus lactis strains. By using a random mutagenesis approach, the gene encoding KdcA in L. lactis B1157 was identified. The gene for this enzyme is highly homologous to the gene annotated ipd, which encodes a putative indole pyruvate decarboxylase, in L. lactis IL1403. Strain IL1403 does not produce KdcA, which could be explained by a 270-nucleotide deletion at the 3' terminus of the ipd gene encoding a truncated nonfunctional decarboxylase. The kdcA gene was overexpressed in L. lactis for further characterization of the decarboxylase enzyme. Of all of the potential substrates tested, the highest activity was observed with branched-chain {alpha}-keto acids. Moreover, the enzyme activity was hardly affected by high salinity, and optimal activity was found at pH 6.3, indicating that the enzyme might be active under cheese ripening conditions.

* Corresponding author. Mailing address: NIZO food research, Department of Flavor, Nutrition and Ingredients, P.O. Box 20, 6710 BA Ede, The Netherlands. Phone: 31 318659532. Fax: 31 318650400. E-mail: Wim.Engels{at}nizo.nl.

Applied and Environmental Microbiology, January 2005, p. 303-311, Vol. 71, No. 1
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.1.303-311.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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