General Microbiology - Schlegel, H. 1987

Decomposition of natural substances
Fructans

Plants of certain families store fructans (also referred to as polyfructosans) instead of, or In addition to, starch (glucans). The tubers of Asteraceae (e.g., dahlias) contain the fructan inulin, although in small amounts. Phlein-type fructans deserve detailed consideration, as they account for 12–15% of the dry weight in forage grasses. Fructan-degrading Enzymes have been isolated from Aspergillus niger and various Bacteria, and they appear to be widespread. However, the exact degradation process of fructans remains poorly understood.

Fructans, also known as levans, are synthesized by a wide range of bacteria when grown on sucrose-containing media. The Mechanism of levan formation is analogous to that of dextrans and is catalyzed by extracellular levansucrase:

Class="center">«Sucrose → Levan + nGlucose

On sucrose media, this exoenzymatic production of levan can be identified by the appearance of small droplets of this polysaccharide adjacent to the colonies (frequently observed in cultures of Bacillus subtilis, B. cereus, and Azotobacter chroococcum). Levan production is also characteristic of Streptococcus salivarius, S. mutans, numerous strains of fluorescent and phytopathogenic pseudomonads, Enterobacter species, and other bacteria. Some strains of levan-producing bacteria, having depleted all available sucrose in the medium, subsequently hydrolyze and reuse the previously synthesized levan.



Last update: 13/08/2026

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