title: Role of cystathionine beta-lyase in catabolism of amino acids to sulfur volatiles by genetic variants of Lactobacillus helveticus CNRZ 32.
abstract: Catabolism of sulfur-containing amino acids plays an important role in the development of cheese flavor. During ripening, cystathionine beta-lyase (CBL) is believed to contribute to the formation of volatile sulfur compounds (VSCs) such as methanethiol and dimethyl disulfide. However, the role of CBL in the generation of VSCs from the catabolism of specific sulfur-containing amino acids is not well characterized. The objective of this study was to investigate the role of CBL in VSC formation by Lactobacillus helveticus CNRZ 32 using genetic variants of L. helveticus CNRZ 32 including the CBL-null mutant, complementation of the CBL-null mutant, and the CBL overexpression mutant. The formation of VSCs from methionine, cystathionine, and cysteine was determined in a model system using gas chromatography-mass spectrometry with solid-phase microextraction. With methionine as a substrate, CBL overexpression resulted in higher VSC production than that of wild-type L. helveticus CNRZ 32 or the CBL-null mutant. However, there were no differences in VSC production between the wild type and the CBL-null mutant. With cystathionine, methanethiol production was detected from the CBL overexpression variant and complementation of the CBL-null mutant, implying that CBL may be involved in the conversion of cystathionine to methanethiol. With cysteine, no differences in VSC formation were observed between the wild type and genetic variants, indicating that CBL does not contribute to the conversion of cysteine.
authors.affiliation: Division of Animal Science and Technology, Gyeongsang National University, Jinju, South Korea.
authors.forename: Won-Jae
authors.initials: WJ
authors.lastname: Lee
authors.forename: Dattatreya S
authors.initials: DS
authors.lastname: Banavara
authors.forename: Joanne E
authors.initials: JE
authors.lastname: Hughes
authors.forename: Jason K
authors.initials: JK
authors.lastname: Christiansen
authors.forename: James L
authors.initials: JL
authors.lastname: Steele
authors.forename: Jeffery R
authors.initials: JR
authors.lastname: Broadbent
authors.forename: Scott A
authors.initials: SA
authors.lastname: Rankin
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D002611:Cheese; D002849:Chromatography, Gas; D002851:Chromatography, High Pressure Liquid; D017931:DNA Primers; D005524:Food Technology / Q000379:methods; D014644:Genetic Variation; D052198:Lactobacillus helveticus / Q000201:enzymology* / Q000235:genetics; D008190:Lyases / Q000378:metabolism*; D013058:Mass Spectrometry; D015394:Molecular Structure; D009154:Mutation / Q000235:genetics; D013455:Sulfur / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D017931:DNA Primers; D013455:Sulfur; D008190:Lyases; C019965:cystathionine beta-lyase