Molds, polysaccharides

In this group we place mainly the neutral bacterial slimes and reserve carbohydrates. They are better defined products than those previously dealt with and as such may of course be regarded as true polysaccharides. Invariably, however, saponification methods are required to rid them of protein residues and to make them water-soluble. The more soluble mold polysaccharides appear to lose their protein constituents by autolytic processes during the longer periods required for mold metabolism. Mold slime production can, however, readily be demonstrated on a solid medium. It is proposed here to give briefly some of the types of structure known in the group. 

Stacey has written an excellent review on the subject of mucopolysaccharides, which he classified on the basis of their containing both hexosamine and hexuronic acid residues, one or the other of these sugar derivatives, or neither. Hyaluronic acid, chondroitinsulfuric acid. Type I pneumococcal polysaccharides, and heparin are members of the first class. Types II, III, and VIII pneumococcal polysaccharides are examples containing hexuronic acid but no hexosamine. Chi tin and Types IV and XIV pneiuno-coccal polysaccharides contain hexosamine but no hexuronic acid and bacterial dextrans, mold polysaccharides, and levans contain neither hexosamine nor hexuronic acid. 

Agar, which is low in metabolizable or inhibitory substances, debris, and thermoduric spores, is ideal for the propagation and pure culture of yeasts, molds, and bacteria. Agar also meets the other requirements of ready solubiUty, good gel firmness and clarity, and a gelation temperature of 35—40°C and a gel melting temperature of 75—85°C. A clarified and purified form of the bacterial polysaccharide, geUan gum, is the only known satisfactory substitute. 

Finally, animal, plant and microbial tissues have been shown to contain the iron storage protein ferritin. The animal protein has been extensively studied, but the mechanism of iron binding has not been completely resolved (29). Animal tissues contain, in addition, a type of granule comprised of iron hydroxide, polysaccharide and protein. The latter, called hemosiderin, may represent a depository of excess iron (30). Interestingly, a protein with properties parallel to those of ferritin has been found in a mold. Here the function of the molecule can be examined with the powerful tools of biochemical genetics (31). 

This review deals with bacterial and related polysaccharides, such as those of molds and yeasts. The bacteriological nomenclature is that of Bergey10 non-systematic nomenclature is indicated by ( ). 

Although polysaccharide metabolic products of molds and yeasts are not strictly bacterial polysaccharides, they are considered briefly here because of similarities in chemical structure (see also page 191). 

The nuclei of the acellular, slime mold Physarium polycephalum contains a /3-D-gaIactan (d.p. 560) bearing phosphate (2.5%) and sulfate (9.6%) groups. One unit in every 13 is branched, but the main structural-feature is 4-O-substituted D-galactopyranosyl units.121 It resembles the exocellular polysaccharide.122... 

Cellulose is the most abundant naturally oeeurring polysaccharide formed out of glucose-based repeat imits, connected by 1,4-beta-glucosidic linkages. Cellulose and its derivatives are widely used as tough versatile materials. Cellulose nitrate, cellulose acetate (CA) and cellulose xanthate (rayon) can be easily molded or drawn into fibers for textile applications, for designing composite materials (safety glass), as thermoplastics etc [80]. 

It is difficult to state whether formation of exocellular polysaccharides is more prevalent among the bacteria, the yeasts, or the molds. However, with bacteria, polysaccharide formation has been studied the most thoroughly. Several yeasts are known to elaborate exopolysaccharides and are excellent sources thereof. Polysaccharide formation by fungi is less frequently observed. However, species of... 

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