Effect of Al(III) on surface properties of Bifidobacterium thermophilum as a function of temperature

The effects of Al(III) on surface properties and lactate accumulation by Bifidobacterium thermophilum were investigated. Bacteria were treated with Al(III) at 37 degrees C and 4 degrees C, then exposed to free radicals or nisin. When exposed to Al(III) at 37 degrees C, the organism exhibited spreading on hydrophobic surfaces and showed high susceptibility to free-radical alteration as indicated by Fe(III) binding, but showed little effect on lactate production in the presence or absence of nisin, even after washing with 2 mM EDTA. At 4 degrees C, there was no increased surface spreading or binding of Fe(III), but protection against nisin action was present. This, however, was abolished after washing with EDTA. It was concluded that membrane fluidity is required to affect membrane lipid rearrangement, resulting in surface spreading and increased susceptibility to peroxidation, whereas only loose binding of Al(III) to membrane surfaces is sufficient to prevent transmembrane channel formation by nisin.