Characterization of surface properties of bacterial spores using optical tweezers

The electric charge and the hydrodynamic coefficient and of bacterial spores are key parameters in protein binding to spores and in the adhesion of spores onto surfaces. Using Optical Tweezers, it is possible to simultaneously measure the charge and the hydrodynamic coefficient of a trapped object. From an accurate analysis of the motion of a single spore confined by an optical trap when external electric or drag forces are applied, we measured the charge of Bacillus subtilis spores. These were purified from a wild type strain and from two isogenic mutants characterized by an altered spore surface. Our technique is able to discriminate the three spore types used and to give important information on the hydrophobic properties of their surface

The sps gene products affect germination, hydrophobicity and protein adsorption of Bacillus subtilis spores

The multilayered surface of the Bacillus subtilis spore is composed of proteins and glycans. While over seventy different proteins have been identified as surface components, carbohydrates associated to the spore surface have not been characterized in details yet. Bioinformatic data suggest that the eleven products of the sps operon are involved in the synthesis of polysaccharides present on the spore surface but an experimental validation is available only for the four distal genes of the operon. Here we report a transcriptional analysis of the sps operon and a functional study performed by constructing and analyzing two null mutants lacking either all or only the promoter proximal gene of the operon. Our results show that both sps mutant spores have apparently normal coat and crust but have a small germination defect and are more hydrophobic than wild type spores. We also show that spores lacking all Sps proteins are highly adhesive and form extensive clumps. In addition, sps mutant spores have an increased efficiency in adsorbing a heterologous enzyme, suggesting the hydrophobic force as a major determinant of spore adsorption and indicating that a deep understanding of the surface properties of the spore is essential for its full development as a surface display platform