Characterization of spore surfaces from a Geobacillus sp. isolate by pH dependence of surface charge and infrared...

The surfaces of spores from a Geobacillus sp. isolated from a milk powder production line were examined to obtain fundamental information relevant to bacterial spore adhesion to materials.

The surfaces of spores were characterized using transmission electron microscopy and infrared spectroscopy. Thin sections of spores stained with ruthenium red revealed an exosporium with a hair-like nap around the spores. Attenuated total reflection infrared spectra of the spores exposed to different pH solutions on a ZnSe prism revealed that pH-sensitive carboxyl and phosphodiester groups associated with proteins and polysaccharides contributed to the spore's negative charge which was revealed by our previous zeta potential measurements on the spores. Lowering the pH to the isoelectric point of spores resulted in an increase in intensity of all spectral bands, indicating that the spores moved closer to the zinc selenide (ZnSe) surface as the charged surface groups were neutralized and the spore surface polymers compressed. The attachment of spores to stainless steel was threefold higher at pH 3 compared with pH 7.

This research showed that spore attachment to surfaces is influenced by electrostatic interactions, surface polymer conformation and associated steric interactions.

The adhesion of thermophilic spores is largely controlled by functional groups of surface polymers and polymer conformation.