Physiological function of the maltose operon regulator, MalR, in Lactococcus lactis

Area of Science:

• Microbiology
• Molecular Biology
• Biochemistry

Background:

• Maltose metabolism in Lactococcus lactis involves an ATP-dependent permease and intracellular enzymes like maltose phosphorylase and beta-phosphoglucomutase.
• The maltose operon regulator (MalR) family, including LacI-GalR transcriptional regulators, is known to control maltose metabolism in some Gram-positive bacteria.
• A gene potentially encoding MalR was identified downstream of the malP gene in L. lactis.

Purpose of the Study:

• To investigate the physiological role of the MalR protein in maltose metabolism within Lactococcus lactis.
• To determine if MalR influences maltose uptake or the activity of key metabolic enzymes.

Main Methods:

• Construction and physiological characterization of a L. lactis mutant deficient in the MalR protein (TMB5004).
• Assessment of maltose fermentation capabilities in wild-type and mutant strains.
• Enzyme activity assays for maltose phosphorylase and beta-phosphoglucomutase.
• Measurement of specific maltose uptake rates at varying maltose concentrations.

Main Results:

• The MalR-deficient mutant (TMB5004) exhibited impaired maltose fermentation but retained growth on glucose and trehalose.
• Enzyme activities of maltose phosphorylase and beta-phosphoglucomutase were unaffected in the mutant.
• The specific maltose uptake rate was significantly lower in the mutant compared to the wild type, with the difference increasing at higher substrate concentrations.

Conclusions:

• The MalR protein in L. lactis belongs to the LacI-GalR family of transcriptional regulators based on amino acid sequence similarity.
• MalR appears to function as an activator of maltose transport, rather than a repressor.
• The study indicates MalR's crucial role in facilitating efficient maltose uptake in L. lactis.