The Exosporium of Bacillus megaterium QM B1551 Is Permeable to the Red Fluorescence Protein of the Coral Discosoma sp.

Abstract

Bacterial spores spontaneously interact and tightly bind heterologous proteins. A variety of antigens and enzymes have been efficiently displayed on spores of <i>Bacillus subtilis</i>, the model system for spore formers. Adsorption on <i>B. subtilis</i> spores has then been proposed as a non-recombinant approach for the development of mucosal vaccine/drug delivery vehicles, biocatalysts, bioremediation, and diagnostic tools. We used spores of <i>B. megaterium</i> QM B1551 to evaluate their efficiency as an adsorption platform. Spores of <i>B. megaterium</i> are significantly larger than those of <i>B. subtilis</i> and of other <i>Bacillus</i> species and are surrounded by the exosporium, an outermost surface layer present only in some <i>Bacillus</i> species and lacking in <i>B. subtilis.</i> Strain QM B1551 of <i>B. megaterium</i> and a derivative strain totally lacking the exosporium were used to localize the adsorbed monomeric Red Fluorescent Protein (mRFP) of the coral <i>Discosoma</i> sp., used as a model heterologous protein. Our results indicate that spores of <i>B. megaterium</i> adsorb mRFP more efficiently than <i>B. subtilis</i> spores, that the exosporium is essential for mRFP adsorption, and that most of the adsorbed mRFP molecules are not exposed on the spore surface but rather localized in the space between the outer coat and the exosporium.