A hydrolase from Lactobacillus sakei moonlights as a transaminase

Enzymatic transamination of amino acids yields α-keto acids and is the initial step for the production of volatile compounds that contribute to the sensory perception of fermented foods such as salami. Lactobacillus sakei is one of the lactic acid bacterial strains commonly used in starter cultures. Although the genome sequence of L. sakei 23K lacks genes encoding typical branched-chain amino acid transaminases, transamination activity and the formation of amino acid-derived volatile metabolites could be demonstrated. A protein purified from L. sakei is held responsible for the transamination activity. By heterologous expression of the corresponding gene in Escherichia coli, we were able to characterize the transamination side activity of an enzyme annotated as a putative acylphosphatase (AcP). A transamination side activity of hen egg white lysozyme (HEWL) was also discovered. Both enzymes showed substrate specificity toward branched-chain and aromatic amino acids. AcP also accepted l-methionine. Activity was optimal at neutral pH for both enzymes, whereas AcP showed a significantly higher temperature optimum (55°C) than that of HEWL (37°C). Kinetic parameters revealed high affinity toward l-leucine for AcP (K(m) = 1.85 mM) and toward l-isoleucine for HEWL (K(m) = 3.79 mM). AcP seems to play a major role in the metabolism of amino acids in L. sakei.

Leuconostoc palmae sp. nov., a novel lactic acid bacterium isolated from palm wine

A novel lactic acid bacterium, strain TMW 2.694(T), was isolated among other lactic acid bacteria from palm wine, an alcoholic beverage produced from the sap of various palm tree species. Strain TMW 2.694(T) is a Gram-positive, facultatively anaerobic, catalase-negative, non-spore-forming coccus, occurring in long chains. Phylogenetic analysis based on 16S rRNA gene sequencing positioned strain TMW 2.694(T) in a distinct line of descent within the genus Leuconostoc, with the closest neighbours being Leuconostoc lactis JCM 6123(T) (98.7 % sequence similarity) and Leuconostoc citreum DSM 5577(T) (98.8 % sequence similarity). Comparative sequencing of the additional phylogenetic markers dnaK and recA confirmed the 16S rRNA gene tree topology. Genomic DNA-DNA similarities of strain TMW 2.694(T) to L. lactis DSM 20202(T) and L. citreum DSM 5577(T) were 45.1 and 17.7 %, respectively. The DNA G+C content is 36.4 mol%. Thus, we propose a novel species within the genus Leuconostoc, with the name Leuconostoc palmae sp. nov. and the type strain TMW 2.694(T) (=DSM 21144(T) =LMG 24510(T)).