Product formation and phosphoglucomutase activities in Lactococcus lactis: cloning and characterization of a novel phosphoglucomutase gene.
Maltose metabolism in Lactococcus lactis involves the conversion of beta-glucose 1-phosphate to glucose 6-phosphate, a reaction which is reversibly catalysed by a maltose-inducible and glucose-repressible beta-phosphoglucomutase (beta-PGM). The gene encoding beta-PGM (pgmB) was cloned from a genomic library of L. lactis using antibodies. The nucleotide sequence of a 5695 bp fragment was determined and six ORFs, including the pgmB gene, were found. The gene expressed a polypeptide with a calculated molecular mass of 24210 Da, which is in agreement with the molecular mass of the purified beta-PGM (25 kDa). A short sequence at the N-terminus was found to be similar to known metal-binding domains. The expression of beta-PGM in L lactis was found to be induced also by trehalose and sucrose, and repressed by lactose in the growth medium. This indicates that beta-PGM does not serve solely to degrade maltose, but that it is also involved in the metabolism of other carbohydrates. The specific activity of beta-PGM during fermentation was dependent on the maltose concentration in the medium. The maximum specific activity of beta-PGM increased by a factor of 4.6, and the specific growth rate by a factor of 7, when the maltose concentration was raised from 0.8 to 11.0 g l-1. Furthermore, a higher amount of lactate produced relative to formate, acetate and ethanol was observed when the initial maltose concentration in the medium was increased. The specific activity of alpha-PGM responded similarly to beta-PGM, but the magnitude of the response was lower. Preferential sugar utilization and alpha- and beta-PGM suppression was observed when L. lactis was grown on the substrate combinations glucose and maltose, or lactose and maltose; maltose was the least-preferred sugar. In contrast, galactose and maltose were utilized concurrently and both PGM activities were high throughout the fermentation.
Qian
Ny
N
Department of Applied Microbiology Lund Institute of Technology Lund University PO Box 124, S-221 00 Lund Sweden.
Stanley
Grant A
GA
Department of Food Technology Victoria University PO Box 14428, MCMC Melbourne, Victoria 8001 Australia.
Bunte
Annicka
A
Department of Applied Microbiology Lund Institute of Technology Lund University PO Box 124, S-221 00 Lund Sweden.
Rdstrm
Peter
P
Department of Applied Microbiology Lund Institute of Technology Lund University PO Box 124, S-221 00 Lund Sweden.
D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D015964:Gene Expression Regulation, Bacterial; D015971:Gene Expression Regulation, Enzymologic; D005798:Genes, Bacterial; D013294:Lactococcus lactis / Q000201:enzymology / Q000235:genetics*; D008969:Molecular Sequence Data; D010733:Phosphoglucomutase / Q000235:genetics*; D016415:Sequence Alignment
D010733:Phosphoglucomutase