Insoluble polysaccharides can be degraded by a set of hydrolytic enzymes formed by catalytic modules appended to one or more non-catalytic carbohydrate-binding modules (CBM). The most recognized function of these auxiliary domains is to bind polysaccharides, bringing the biocatalyst into close and prolonged vicinity with its substrate, allowing carbohydrate hydrolysis. Examples of insoluble polysaccharides recognized by these enzymes include cellulose, chitin, beta-glucans, starch, glycogen, inulin, pullulan, and xylan. Based on their amino acid similarity, CBMs are grouped into 55 families that show notable variation in substrate specificity; as a result, their biological functions are miscellaneous. Carbohydrate or polysaccharide recognition by CBMs is an important event for processes related to metabolism, pathogen defense, polysaccharide biosynthesis, virulence, plant development, etc. Understanding of the CBMs properties and mechanisms in ligand binding is of vital significance for the development of new carbohydrate-recognition technologies and provide the basis for fine manipulation of the carbohydrate-CBM interactions.

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Microbial secondary metabolites are low molecular mass products, not essential for growth of the producing cultures, but very important for human health. They include antibiotics, antitumor agents, cholesterol-lowering drugs, and others. They have unusual structures and are usually formed during the late growth phase of the producing microorganisms. Its synthesis can be influenced greatly by manipulating the type and concentration of the nutrients formulating the culture media. Among these nutrients, the effect of the carbon sources has been the subject of continuous studies for both, industry and research groups. Different mechanisms have been described in bacteria and fungi to explain the negative carbon catabolite effects on secondary metabolite production. Their knowledge and manipulation have been useful either for setting fermentation conditions or for strain improvement. During the last years, important advances have been reported on these mechanisms at the biochemical and molecular levels. The aim of the present review is to describe these advances, giving special emphasis to those reported for the genus Streptomyces.

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A mixed culture formed by Bacillus sp. and Geotrichum sp. produced tobacco aroma compounds from the carotenoid lutein through the formation of the intermediate beta-ionone. Both microorganisms can grow independently in a medium supplemented with lutein, but only Geotrichum produces beta-ionone. This intermediate was incorporated by the bacilli, converted to aroma and this product excreted to the culture medium. Bacillus sp. did not utilize beta-ionone for growth but modified it. We conclude that, in the bioconversion of lutein to products with tobacco aroma, Geotrichum sp. is involved in carotenoid oxidation to produce beta-ionone and Bacillus sp. is responsible for the norisoprenoid reduction to produce 7,8-dihydro-beta-ionone and 7,8-dihydro-beta-ionol.