Glucan common to the microcyst walls of cyst-forming bacteria

Abstract

Chemical analysis indicated that D-glucose is tha major neutral monosaccharide present in the microcysts of a range of gram-negative bacteria. Varying amounts of other neutral sugars were found. The glucose was mainly present as a glucan that could be extracted from microcysts of representative strains with alkali or mild acid treatment. The glucan could be identified as an alpha-1,3-linked polymer on the basis of (i) periodate resistance of the extracted polymer and the material present in microcysts; (ii) lectin agglutination of the microcysts; (iii) lectin precipitation of the extracted glucans; and (iv) susceptibility of the glucan either in the walls or after extraction to a specific alpha-1,3-glucanase from Aspergillus nidulans, yielding glucose as the sole hydrolysis product. The galactosamine found in microcysts of Myxococcus xanthus by other workers is clearly a component of another polymer, distinct from the glucan. The presence of an alpha 1,3-linked glucan, common to microcyst walls of various bacterial genera, probably contributes to the rigidity of the walls of these forms and, inter alia, to their resistance to ultrasonic treatment. Preliminary experiments indicate that the gulcan is discarded on germination of the microcysts rather than being broken down by specific enzymes.