Abstract
BackgroundMaltose 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 β-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.ResultsA 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 β-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.ConclusionAccording 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 β-phosphoglucomutase, MalR of L. lactis is considered rather as an activator than a repressor.
Highlights
Maltose metabolism is initiated by an ATP-dependent permease system in Lactococcus lactis
The b-PGM encoding gene, pgmB, is located in a putative trehalose operon, including the genes likely to encode a regulatory protein and the trehalose-specific components of the phosphotransferase system as well as the gene encoding the newly characterised trehalose 6-phosphate phosphorylase [5,6]. malP, encoding the maltose phosphorylase (MP) has been localised in an operon including the genes likely to be involved in poly, oligo
maltose operon regulator (MalR) does not regulate the activity of MP and b-PGM in L. lactis L. lactis mutants harbouring pTMB5003 were screened for impaired maltose catabolism by testing their inability to ferment maltose in liquid medium containing maltose and erythromycin
Summary
Maltose metabolism is initiated by an ATP-dependent permease system in Lactococcus lactis. The purpose of this study was to investigate the physiological role of the MalR protein in maltose metabolism in L. lactis. The subsequent degradation of intracellular maltose is performed by the concerted action of Pi-dependent maltose phosphorylase (MP) and b-phosphoglucomutase (b-PGM) [2,3]. A gene possibly coding for a transcriptional regulator, called MalR, belonging to the LacI-GalR family has been observed downstream of malP[3,5]. In both Staphylococcus xylosus and Streptococcus pneumoniae, maltose metabolism has been shown to be dependent on a maltose operon regulator, MalR [7,8]. By investigating the activities of maltose uptake, MP and b-PGM, the influence of MalR on maltose and trehalose catabolic operons could be assessed
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