Human transferrin as a source of iron for Streptococcus intermedius

Area of Science:

• Microbiology
• Infectious Diseases
• Bacterial Pathogenesis

Background:

• Streptococcus intermedius is a known pathogen causing severe infections.
• Understanding how bacteria acquire essential nutrients like iron is crucial for explaining pathogenesis.

Purpose of the Study:

• To investigate the mechanism by which Streptococcus intermedius utilizes human transferrin as an iron source.
• To identify the specific pathways involved in iron acquisition from transferrin by S. intermedius.

Main Methods:

• Cultivating S. intermedius in iron-deficient media supplemented with iron sources (ferrous sulfate, holotransferrin).
• Analyzing bacterial growth and gene expression under iron-limited conditions.
• Assessing siderophore, reductase, transferrin-binding, and proteolytic activities.
• Monitoring and manipulating the pH of the culture medium.

Main Results:

• S. intermedius growth was supported by ferrous sulfate and holotransferrin in iron-deficient media.
• Iron-poor conditions led to the overexpression of a 58 kDa cell surface protein.
• No siderophore, reductase, transferrin-binding, or proteolytic activity was detected.
• S. intermedius rapidly lowered the medium pH, releasing iron from holotransferrin.
• Increased buffering capacity inhibited growth, indicating pH-dependent iron release.

Conclusions:

• Streptococcus intermedius acquires iron from transferrin primarily by acidifying the surrounding environment.
• This pH-lowering mechanism facilitates iron release from holotransferrin, supporting bacterial growth.
• The findings suggest a novel mechanism for S. intermedius pathogenesis, involving localized environmental modification.