Binding of Fe(OH)3 to Lactobacillus delbrueckii ssp. bulgaricus and Lactobacillus acidophilus: Apparent Role of Hydrogen Peroxide and Free Radicals

Abstract

Lactobacillus delbrueckii ssp. bulgaricus and Lactobacillus acidophilus, both used extensively as probiotics and to produce fermented milk products, were investigated for their ability to bind Fe(OH)3 as a function of time in the presence and absence of approximately 200 μM H2O2 and in the presence and absence of glucose. There was a very rapid initial phase, followed by a second slow phase, and, when fermentable sugar was absent, a third rapid phase. Thermodynamic parameters were determined for the initial rapid binding phase using Scatchard plots. The binding process was entropy driven against an enthalpy barrier, indicating that hydrophobic-type bonding was involved. Results were similar for both species of lactobacilli, and in the presence or absence of glucose and/or H2O2. In the later phases, binding of Fe(OH)3 was decreased if carried out without H2O2 in the medium. Free radicals, apparently produced from H2O2 and iron, were able to alter cell surfaces to allow for greater binding of Fe(OH)3. The ability of probiotics to bind Fe(OH)3 may serve to limit the availability of iron to pathogenic microorganisms. Keywords: Iron; Fe(OH)3; lactobacilli; hydrogen peroxide; free radicals; probiotics