## 5 Biological Properties and Applications  
Many SMs possess useful biological properties or have biotechnological applications [101], while others are detrimental or have disadvantageous effects [102; 103]. SMs useful for humans include a large diversity of antibiotics. In addition to the historical example of penicillin, there are numerous SMs with a very varied spectrum of antibiosis. Among them are other antibacterial, such as cephalospororin obtained from _Acemonium chrysogenum_[104], antifungals, such as griseofulvin produced by _Penicillium_ or other fungi [105], or antiprotozoals, such as bikaverin synthesized by _Fusarium_ species [14]. Other compounds have medical or pharmaceutical applications, such as immunosuppressant cyclospor A, produced by _Tolypocladium inflatum_[16]; cholesterol-lowering statins, withlovastatin from _Aspergillus terreus_ as the best known example [12]; vitamin-A precursor \(\beta\)-carotene, industrially obtained from _Blakeslea trispora_[106]; and anticancer drugs, such as the indole alkaloid camptothecin and taxol, produced by the endophytic fungus _Entrophospora inftequens_[107] and _Taxonyces andreanae_[108], respectively. An outstanding case in biotechnological applications is the aforementioned gibberellins, growth-regulating plant hormones with agricultural applications, which are mostly represented by gibberellic acid obtained from _F. fujikuroi_[27]. Frequently, secondary metabolites absorb visible light and have striking colors, ranging across all ranges of the spectrum: e.g., bikaverin and fusarubin have a reddish pigmentation [28]. In some cases, although it is not related to their biological function, different SMs are used commercially as pigments. Among them some carotenoids stand out, such as astaxanthin. This pigment, produced by the yeast _Xhantophyllomyces dendrohous_[109] and some algae, is used in aquaculture as feed additive to provide an orange color to certain fish and crustaceans. Other well-known fungal pigments are polyketides produced by _Moniscus purpurea_[110], a fungus used in rice fermentation since ancient times in Chinese and Japanese cuisine. These polyketides include monascorubramine as well as rubropunctatin and its derivatives, which are of various yellowish, orange, or reddish colors, and to which numerous healthy properties are attributed, such as anticancer, antidiabetic, or antiobesity properties. Regardless of their real roles in nature, many SMs are toxic to humans, and their presence in plant foods, due to contamination by producing fungi before or after the harvest, constitutes an important public health problem [102; 103; 111]. These harmful SMs are known generically as mycotoxins. One specially studied for its high toxicity is aflatoxin B1, produced by various species of _Aspergillus_[112]. Its consumption is associated with a syndrome known as acute aflatoxicosis, as well as with liver cancer or other damaging effects [103]. Many well-known mycotoxins are produced by the _Fusarium_ species [113], among them fumonisins, zearalenones, trichothecenes, and fusarins. Fumonisins inhibit sphingolipid metabolism and also have carcinogenic properties. A correlation between their consumption and esophageal cancer is well documented [102]. Trichothecenes inhibit protein synthesis and produce toxic syndromes in humans and animals. A well-known trichothecene is deoxynivalenol, which produces alimentary toxic alekuka, acute gastroenteritis, and growth impairment, among other effects [103]. Fusarins, especially fusarin C, are mutagenic in the Ames test, presumably due to their transformation into more toxic derivatives in the body [114]. Another mutagenic mycotoxin is ochratoxin A, which provokes renal cancer [102]. Zearalenones have lower toxicity, but produce an estrogenic syndrome in pigs, presumably due to their resemblance to this family of hormones [103]. An interesting consequence of the large metabolic diversity of fungi is that different species produce specific patterns of SMs, which allow for their use in taxonomic studies.