Physiological function of the maltose operon regulator, MalR, in Lactococcus lactis.
BACKGROUND
Maltose metabolism is initiated by an ATP-dependent permease system in Lactococcus lactis. The subsequent degradation of intracellular maltose is performed by the concerted action of Pi-dependent maltose phosphorylase and beta-phosphoglucomutase. In some Gram-positive bacteria, maltose metabolism is regulated by a maltose operon regulator (MalR), belonging to the LacI-GalR family of transcriptional regulators. A gene presumed to encode MalR has been found directly downstream the maltose phosphorylase-encoding gene, malP in L. lactis. The purpose of this study was to investigate the physiological role of the MalR protein in maltose metabolism in L. lactis.


RESULTS
A L. lactis ssp. lactis mutant, TMB5004, deficient in the putative MalR protein, was physiologically characterised. The mutant was not able to ferment maltose, while its capability to grow on glucose as well as trehalose was not affected. The activity of maltose phosphorylase and beta-phosphoglucomutase was not affected in the mutant. However, the specific maltose uptake rate in the wild type was, at its lowest, five times higher than in the mutant. This difference in maltose uptake increased as the maltose concentration in the assay was increased.


CONCLUSIONS
According to amino acid sequence similarities, the presumed MalR is a member of the LacI-GalR family of transcriptional regulators. Due to the suggested activating effect on maltose transport and absence of effect on the activities of maltose phosphorylase and beta-phosphoglucomutase, MalR of L. lactis is considered rather as an activator than a repressor.
Andersson
Ulrika
U
Applied Microbiology, Center for Chemistry and Chemical Engineering, Lund Institute of Technology, Lund University, PO Box 124, SE-221 00 Lund, Sweden. andersson.veb@swipnet.se
Rådström
Peter
P
D001426:Bacterial Proteins; D001692:Biological Transport; D029968:Escherichia coli Proteins / Q000737:chemistry; D015964:Gene Expression Regulation, Bacterial; D005964:Glucosyltransferases / Q000378:metabolism; D056968:Lac Repressors; D013294:Lactococcus lactis / Q000235:genetics / Q000502:physiology*; D008320:Maltose / Q000378:metabolism*; D008969:Molecular Sequence Data; D010733:Phosphoglucomutase / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry / Q000502:physiology*; D014157:Transcription Factors / Q000502:physiology
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; C050993:Galactose repressor proteins; D056968:Lac Repressors; D012097:Repressor Proteins; D014157:Transcription Factors; C084528:malR protein, bacteria; D008320:Maltose; D005964:Glucosyltransferases; C021535:maltose phosphorylase; D010733:Phosphoglucomutase