title: Dissolution of xylose metabolism in Lactococcus lactis.
abstract: Xylose metabolism, a variable phenotype in strains of Lactococcus lactis, was studied and evidence was obtained for the accumulation of mutations that inactivate the xyl operon. The xylose metabolism operon (xylRAB) was sequenced from three strains of lactococci. Fragments of 4.2, 4.2, and 5.4 kb that included the xyl locus were sequenced from L. lactis subsp. lactis B-4449 (formerly Lactobacillus xylosus), L. lactis subsp. lactis IO-1, and L. lactis subsp. lactis 210, respectively. The two environmental isolates, L. lactis B-4449 and L. lactis IO-1, produce active xylose isomerases and xylulokinases and can metabolize xylose. L. lactis 210, a dairy starter culture strain, has neither xylose isomerase nor xylulokinase activity and is Xyl(-). Xylose isomerase and xylulokinase activities are induced by xylose and repressed by glucose in the two Xyl(+) strains. Sequence comparisons revealed a number of point mutations in the xylA, xylB, and xylR genes in L. lactis 210, IO-1, and B-4449. None of these mutations, with the exception of a premature stop codon in xylB, are obviously lethal, since they lie outside of regions recognized as critical for activity. Nevertheless, either cumulatively or because of indirect affects on the structures of catalytic sites, these mutations render some strains of L. lactis unable to metabolize xylose.
authors.affiliation: Department of Food Science, Cornell University, Ithaca, New York 14853, USA.
authors.forename: K A
authors.initials: KA
authors.lastname: Erlandson
authors.forename: J H
authors.initials: JH
authors.lastname: Park
authors.lastname: Wissam
authors.lastname: El Khal
authors.forename: H H
authors.initials: HH
authors.lastname: Kao
authors.forename: P
authors.initials: P
authors.lastname: Basaran
authors.forename: S
authors.initials: S
authors.lastname: Brydges
authors.forename: C A
authors.initials: CA
authors.lastname: Batt
mesh_terms: D019747:Aldose-Ketose Isomerases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013294:Lactococcus lactis / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009876:Operon; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014994:Xylose / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D014157:Transcription Factors; C074322:XylR protein, Pseudomonas; D014994:Xylose; D017853:Phosphotransferases (Alcohol Group Acceptor); C032700:xylulokinase; D019747:Aldose-Ketose Isomerases; C023298:xylose isomerase