The Fusaric Acid

The genus Fusarium contains important species of mycotoxin producers which have caused a series of human diseases such as aleukia toxic food, Urov or Kashin-Beck disease, intoxication Akakabi byo-grain, itchy, and esophageal cancer. Many of these species also have caused several animal diseases, including hemorrhagic syndromes, lack of appetite, toxicosis moldy in sweet potato, bean hulls poisoned, and leucoencephalomalacia of horses.

Interest in Fusarium species are increasing worldwide due to the discovery of an increasing number of naturally occurring Fusarium of mycotoxins that has practical importance as threats to human and animal health. Mycotoxins produced by Fusarium species have variable numbers of structure. Often a number of combinations can be similar to identified in a group, such as nitrogen tricothecenos without their structures, and licomarasminas fumonisins with a lack of amine. Mycotoxins from Fusarium can lixiviate into the soil, causing damage to plants and animals even after the fungus is no longer active. Indeed, a risk which can be extrapolated for humans as well.

Mycotoxins produced by Fusarium oxysporum are many, among them: diacetoxyscirpenol, diacetilnivalenol, fumonisins, fusarenon-X, fusaric acid, 7 "-hidroxidiacetoxiscirpenol, moniliformin, neosolaniol, T-2 toxin and zearalenone.

Fusaric acid is considered the most important toxic secondary metabolite produced by the fungus Fusarium oxysporum (Marasas et al., 1984). The low molecular weight displayed by this mycotoxin favors its displacement through the transpiration stream, reaching the leaves of the host, where they act disrupting the permeability of cell membranes and the capacity of controlling water loss from perspiration (Davis, 1969; Ouchi et al, 1989; Hillocks Marley, 1993). It is important to emphasize that the fumaric acid has been reported as inhibitor of human adenocarcinoma cells(Fernandez-Pol et al., 1993).

Many economically important crops such as corn, rice, wheat, sorghum and barley are affected by Fusarium (Yasue, 1949, Reis et al., 1995; Pinto, 1996; Goulart and Fialho, 1998); also in other fruits like the yellow passion fruit (Flores et al., 2012). The incidence of these fungi usually occurs by natural infection in the field, favored by wet weather and warm in the stage of pollination, poor mulching and insect damage (Shurtleff, 1992, Reid et al.1996).

Figure 1 – Photo of corn cob (Zea mays) contaminated with Fusarium sp. (Source: Carlos Antonio Locatelli)

The biosynthesis of fusaric acid in Fusarium species is regulated by the availability of carbon and nitrogen in the medium having the optimal relationship with C: N of 5:1 (Diniz, 1999). The researcher observed morphological and anatomical changes in roots of maize promoted by fusaric acid. These changes led to acceleration in the process of cellular differentiation leading to the shortening of the root, due to the decrease of the region of elongation (Diniz and Oliveira, 2009). These cytotoxic effects of fusaric acid were decreased by the use of fitohormonais regulators, among them, indoleacetic and gibberelic acids and besides kinetin.

Nitrogen supply seems to be a factor in the biosynthesis of fusaric acid, this would explain the preference of the organisms senescent in infected tissues than in young tissue (Sarhan et al., 1982). A. napiforme, F. heterosporum, F. solani and F. proliferatum interacts with several hormones and its effect on plant development has not been completely elucidated. Certainly, the relative protection offered by the substances phytoregulators plant tissue against the cytotoxic action of fusaric acid, is the result of conditioning that this tissue was submitted. Since the growth regulators are substances that optimize cellular metabolism, they would be agents to protect the plant tissue (Diniz, 1999).

The Fusarium is the most important pathogen of maize, Zea mays, causing seed rot, stem and spike as described by MacDonald and Chapman (1997). The invasion of the pathogen is through the parenchyma of the root meristem, extending the primary vessels and trachea (Hepple, 1963; Khadr and Snyder, 1967; Penny Packer and Nelson, 1972).  Fusarium species not only produce this mycotoxin but other secondary metabolites such as fumonisin, deoxynivalenol, nivalenol and zearalenone (Turner, 1971, Abbas et al., 1995), which exert different effects on plant and animal tissues (Bacon et al., 1995).

This acid was first isolated by Yabuta and collaborators in 1934 in Japan as a metabolic product of Fusarium heterosporum Ness, infecting plants, and was subsequently identified as Fusarium verticillioides Sheld.

The presence of this toxin was confirmed by Gaumann et al.(1952), also in 1952 other species such as Fusarium lycopersici, Fusarium vasinfectum, Fusarium verticillioides and still Gibberella fujikuroi. Later in 1957, this same group of researchers reported the production of this mycotoxin fungi family called Hypocreaceae. A total of 46 strains of Fusarium oxysporum and the production of fusaric acid were obtained in 1969 by Davis.

The fungi that produce fusaric acid were divided into three classes depending on the levels of toxin synthesis, low producers: 1-100 µg g-1; moderate producers 100-500 µg g-1, and high producers above 500 µg g-1 dry weight of the grain from which they were isolated.

Bacon and collaborators in 1996 recorded the fusaric acid production were of 78 strains from Fusarium verticillioides, F. crookwellense, F. subglutinans, F. sambucinum. Also were registered the occurrence of fusaric acid and 9,10-dehydro-fusaric in isolates of Fusarium nygamai, F. semifectum, Cephalosporium spp, Alternaria, according to studies by Abbas (1995), Capasso et al.(1996), Diniz (1999). The production of secondary metabolites by Fusarium oxysporum, among which the fusaric acid was reported by Savard et al., 1997 and Eged and Srobarova in 1997.

This fungus occurs as a saprophyte or parasite non-specific scavenger in grasses, including maize, rice, wheat, sorghum, and barley (Ayers et al., 1975).

Figure 2 -  Molecular structure of fusaric acid

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Capasso, R. Evidente, A; Cutignano, A; Vurro, M.; Zonno, M.C.; Bottalico, A. 1996. Fusaric and 9,10-dehydrofusaric acids and their methyl esters from Fusarium nygamai. Phytochemistry, v.41, p.1035-1039.

Davis, D. 1969. Fusaric acid in selective pathogenicity of Fusarium oxysporum.Phytopathology, v.59, p.1391-1395.

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spssDiniz – March, 31, 2018