Lectin binding on surfaces of Frankia strains

Abstract

As a prerequisite for the formation of symbiotic association the two partners must come in contact at their cell surfaces, where the phenomena of specificity and recognition are believed to take place. Therefore, in the case of actinorhizal symbioses, probing of Frankia cell surfaces was investigated with fluorescein-labelled lectins as specific markers for sugar residues. Eleven Frankia isolates grown in vitro and originating from Alnus and Elaeagnus host-plant specificity groups were tested with lectins of different carbohydrate-binding specificities. The N-acetylglucosamine and sialic acid binding lectin groups were able to bind to cell surfaces of both type-N and type-P strains of the Alnus group but not to any Frankia strains of the Elaeagnus group. Sugar residues recognized by these lectin groups on colonies of Frankia strains of the Alnus group were detected on hyphae, vesicles, and sporangia but not on mature spores. The present lectin binding study demonstrates that the use of lectins as bioprobes can be a valid tool in the awaited species definition in the genus Frankia.