Presence and function of a thick mucous layer rich in polysaccharides around Bacillus subtilis spores

Abstract

This study was designed to establish the presence and function of the mucous layer surrounding spores of Bacillus subtilis. First, an external layer of variable thickness and regularity was often observed on B. subtilis spores. Further analyses were performed on B. subtilis 98/7 spores surrounded by a thick layer. The mechanical removal of the layer did not affect their resistance to heat or their ability to germinate but rendered the spore less hydrophilic, more adherent to stainless steel, and more resistant to cleaning. This layer was mainly composed of 6-deoxyhexoses, ie rhamnose, 3-O-methyl-rhamnose and quinovose, but also of glucosamine and muramic lactam, known also to be a part of the bacterial peptidoglycan. The specific hydrolysis of the peptidoglycan using lysozyme altered the structure of the required mucous layer and affected the physico-chemical properties of the spores. Such an outermost mucous layer has also been seen on spores of B. licheniformis and B. clausii isolated from food environments.

Keywords:

• Bacillus subtilis spore
• mucous layer
• physico-chemistry
• adhesion
• saccharidic composition

Acknowledgements

This work was financed by the Agence Nationale de la Recherche under the Programme National de Recherche en Alimentation et Nutrition Humaine project ANR-07-PNRA-009, InterSpore. The authors are grateful to Jean-François Migdal and Martine Clarisse, from INRA UR638, for technical assistance.