General Microbiology - Schlegel, H. 1987

Degradation of natural substances
Agar

Agar is a mixture of agarose and agaropectin. The main polysaccharide consists of alternating residues of D-galactose and 3,6-anhydrogalactose linked in a linear chain by ß-1,4 and 1,3 bonds. Agaropectin has a more complex Structure, comprising D-galactose, 3,6-anhydrogalactose, corresponding uronic acids, and sulfate. Agar is found in red Algae, but commercial production relies on species of Gelidium.

The vast majority of microorganisms are unable to degrade agar. Only a few bacterial species capable of hydrolyzing it have been isolated from seawater and algae. The hallmark of agar degradation by such Bacteria is the sinking of their colonies into the agar layer (Fig. 14.3). Agar-degrading bacteria are most commonly found in marine biotopes. In the tidal zone, their count reaches about 107 per 1 g of silt (accounting for 2-4% of the total aerobic bacteria present in these habitats). Species capable of breaking down agar are found within the genera Cytophaga, Flavobacterium, Bacillus, Pseudomonas, and Alcaligenes.



Last update: 13/08/2026

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