Indiana University South Bend, South Bend, IN 46634-7111
Bifidobacterium is an anaerobic high GC actinobacterial genus with members frequently associated with human and animal intestines and considered as probiotic organisms for gastrointestinal health. B. scardovii is a rare isolate from a human blood sample but its role in the human body has not been elucidated. In the laboratory, it can be cultured with various growth media under anaerobic conditions. Intracellular granules that stained strongly to cationic dyes were observed in cells grown in commercial Lactobacilli MRS medium (MRS), which contains 2% glucose, but not in Reinforced Clostridial Medium (RCM) or on blood agar plates, which contain 0.5% or 0% glucose, respectively. Cells from RCM cultures supplemented with 2% glucose were found to form granules, indicating that carbohydrate and carbon abundance may play a role in granule formation. In order to determine possible physiological functions of intracellular granule formation in B. scardovii, acid tolerance was examined in cells grown in MRS and RCM. The MRS-grown cells showed a 2.4-fold higher survival rate than that from RCM cultures when incubated in pH3.5 RCM broth for 60 min, suggesting that intracellular granules may be linked to acid tolerance in vivo. Furthermore, we measured surface hydrophobicity of B. scardovii cells from MRS and RCM cultures. We showed that surface hydrophobicity of B. scardovii cells grown in MRS was nearly twice that of RCM-grown cells. Since previous studies suggested that cell surface hydrophobicity is positively linked to bifidobacterial adhesion to host cells, we propose that intracellular granule formation might also be involved in adhesion to host cells in vivo. Interestingly, the cell extract from recombinant E. coli containing a B. scardovii glucosidase/xylosidase construct caused a 27% reduction in surface hydrophobicity in MRS-grown B. scardovii cells when compared to cells that were treated with an E. coli cell extract from a vector control, implying that sugar moieties might contribute to surface hydrophobicity.
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