Rahman MM, Kim WS, Ito T, Kumura H, Shimazaki K
Lactoferrin, a major whey protein of human milk, is considered as growth promoter for bifidobacteria, the predominant microorganisms of human intestine. In the present study, in vitro growth promotion and cell binding ability of bovine lactoferrin to several strains of Bifidobacterium longum have been demonstrated. A dose-dependent as well as strain-dependent growth promotion effect by lactoferrin was observed. Cell binding ability of lactoferrin was inspected under an inverted confocal laser scanning microscope by incubation bacterial cells with biotinylated bovine lactoferrin and FITC-conjugated avidin. Fluorescence staining showed bovine lactoferrin binding to all tested strains. A lactoferrin-binding protein with a molecular weight of approximately 67 kDa was also detected in the extracted membrane and cytosolic fraction of each B. longum strain by far-Western blot technique using biotinylated lactoferrin and horseradish peroxidase-conjugated streptavidin. Based on these results, we suggest that existence of lactoferrin-binding protein could be a common characteristic in bifidobacteria. It can also be hypothesized that lactoferrin-binding protein in bifidobacteria is not only involved in growth stimulation mechanism but also could play different roles.