Saturday, 9 February 2019

Toxins of Fusarium

Toxins of Fusarium

Antibiotic Y
Antibiotic Y has significant antibiotic properties towards phytopathogenic bacteria but low cell toxicity (Golinski et al., 1986). However, this compound, which originally was named lateropyrone (Bushnell et al., 1984), has not been studied in detail. Producers of antibiotic Y are widespread and common in agricultural products, so the natural occurrence of antibiotic Y may be of importance. Natural occurrence in cherries, apples and wheat grains has been reported (Andersen and Thrane, 2005).

Major sources. The main producer is Fusarium avenaceum which occurs frequently in cereal grain, fruit and vegetables. Another consistent producer is F. tricinctum, which also is very frequently found on cereal grains in temperate climates.

Minor sources. F. lateritium is known as a plant pathogen, but also causes spoilage in fruits and has been reported from apples and cherries in which antibiotic Y was detected (Andersen and Thrane, 2006). In warmer climates F. chlamydosporum is a potential producer of antibiotic Y in cereal grain and other seeds.

Butenolide is a collective name for compounds with a given ring structure; however in Fusarium mycotoxicology butenolide is a synonym for 4-acetamido-2-buten-4-olide, which has been associated with cattle diseases (fescue foot) since the mid 1960s (Yates et al., 1969). The toxicology has been thoroughly discussed by Marasas et al. (1984). There have been no reports of butenolide in foods, but it may be an important toxin due to the reported synergistic effect with enniatin B (Hershenhorn et al., 1992).

Major sources. The original reported producer of butenolide is F. sporotrichioides [reported as F. nivale, see Marasas et al. (1984) for details] and other frequent producers of butenolide in cereals are F. graminearum and F. culmorum.

Minor sources. Other potential producers of butenolide are F. avenaceum, F. poae and F. tricinctum which are frequently found in cereal grains together with F. crookwellense, F. sambucinum and F. venenatum. The latter three species also can be found in potatoes and other root vegetables.

Culmorin has a low toxicity in several biological assays (Pedersen and Miller, 1999) but a synergistic effect with deoxynivalenol towards caterpillars has been demonstrated (Dowd et al., 1989). Culmorin and hydroxyculmorins have been detected in cereals (Ghebremeskel and Langseth, 2000). These samples also contained deoxynivalenol and acetyl-deoxynivalenol.

Major sources. F. culmorum and F. graminearum, found in cereals, are the major producers of culmorin. The less widely distributed species F. poae and F. langsethiae are also consistent producers of culmorin and derivatives (Thrane et al., 2004).

Minor sources. Other species producing culmorin are F. crookwellense and F. sporotrichioides, also found in cereals.

Cyclic Peptides
The two groups of cyclic peptides, beauvericin and enniatins, are structurally related and they show antibiotic and ionophoric activities (Kamyar et al., 2004). Both groups of cyclic peptides have been
detected in agricultural products (Jestoi et al., 2004).

Beauvericin was originally found in entomopathogenic fungi such as Beauveria bassiana and Isaria fumosorosea (formerly Paecilomyces fumosoroseus; Luangsa-Ard et al., 2005) but has also been detected in several Fusarium species occurring on food (Logrieco et al., 1998). Major sources. Fusarium subglutinans, F. proliferatum and F. oxysporum are consistent producers of beauvericin and have often been found to produce high quantities under laboratory conditions. These species are often found on maize and fruits. Minor sources. Several species of the Gibberella fujikuroi complex have been reported to produce beauvericin in low amounts, including F. nygamai, F. dlaminii and F. verticillioides from cereals and fruits. The systematics of these Fusaria has developed dramatically during the last years, so a lot of species specific information of toxin production is not available.

Enniatins are a group of more than 15 related compounds produced by several Fusarium species, but also from Halosarpeia sp. and Verticillium hemipterigenum; however these are not of food origin. Major sources. Fusarium avenaceum is the most important enniatin producer in cereals and other agricultural food plants, because this species is a very frequent and consistent producer of enniatin B (Morrison et al., 2002). Fusarium sambucinum is a consistent producer of enniatin B and diacetoxyscirpenol and causes dry rot in potatoes; however the role of these toxins has not been examined. Minor sources. F. langsethiae, F. poae and F. sporotrichioides, mainly occur on cereal grain, F. lateritium from fruits and F. acuminatum from herbs.

Since the discovery of fumonisins in the late 1980s much attention has been paid to these highly toxic compounds. Several reviews on the chemistry, toxicology and mycology have been published (Marasas et al., 2001; Weidenb├Ârner, 2001).

Major sources. F. verticillioides (formerly known as F. moniliforme; Seifert et al., 2003) and F. proliferatum are the main sources of fumonisins in maize. These species and fumonisins in maize and to a lesser extent other cereal crops have been reported from all over the world in numerous papers and book chapters. Minor sources. Other fumonisin producing species are Fusarium nygamai, F. napiforme, F. thapsinum, F. anthophilum and F. dlamini from millet, sorghum and rice. Some strains of these species have also been isolated from soil debris.

Fusaproliferin is a recent discovered mycotoxin which shows teratogenic and pathological effects in cell assays (Bryden et al., 2001).Fusaproliferin has been detected in natural samples together with beauvericin and fumonisin (Munkvold et al., 1998). Nothing is known about a possible synergistic effect in such toxin combinations. Major sources. Fusarium proliferatum and F. subglutinans are themajor sources in maize and other cereal grains. The fungi and fusaproliferin have been detected in Europe, North America and South Africa (Wu et al., 2003).

Minor sources. A few strains of F. globosum, F. guttiforme, F. pseudocircinatum, F. pseudonygamai and F. verticillioides have been found to produce fusaproliferin, however the systematics in this section of Fusarium has developed dramatically within recent years so specific information on the toxin production by recently described species is unknown.

Moniliformin is cytotoxic, inhibits protein synthesis and enzymes, causes chromosome damages and induces heart failure in mammals and poultry (Bryden et al., 2001). Moniliformin has been found world wide in cereal samples Major sources. In maize F. proliferatum and F. subglutinans are the main producers of moniliformin, whereas F. avenaceum and F. tricinctum are the key sources in cereals grown in temperate climates. Minor sources. In sorghum, millet and rice F. napiforme, F. nygamai, F. verticillioides and F. thapsinum may be responsible for moniliformin production. Some strains of F. oxysporum produce a significant amount of moniliformin under laboratory condition; however there is no detailed information on a possible production in vegetables and fruits. An overview of other minor sources has been published (Sch├╝tt et al., 1998).

More than 200 trichothecenes have been identified and the nonmacrocyclic trichothecenes are among the most important mycotoxins. Trichothecenes are haematotoxic and immunosuppressive. In animals, vomiting, feed refusal and diarrhoea are typical symptoms. Skin oedema in humans has also been observed. An EU working group on has reported on trichothecenes in food (Schothorst and van
Egmond, 2004).

Deoxynivalenol (DON) and Acetylated Derivatives
Deoxynivalenol (DON) and its acetylated derivatives (3ADON, 15ADON) are by far the most important trichothecenes. Numerous reports on world-wide occurrence have been published and several international symposia and workshops have focussed on DON (Larsen et al., 2004). Major sources. Fusarium graminearum and F. culmorum are consistent producers of DON, especially in cereals. Within both species strains have been grouped into those that produce DON and its derivatives, and those that produce nivalenol and furarenon X as their major metabolites. Intermediates have also been found (Nielsen and Thrane, 2001). Recently, F. graminearum has been divided into nine phylogenetic species (O’Donnell et al., 2004); however in the present context this species concept will not be used as a correlation to existing mycotoxicological literature is impossible at this stage.

Nivalenol (NIV) and Fusarenon X (FX, 4ANIV)
Nivalenol (NIV) and fusarenon X (FX, 4ANIV) occur in the same commodities as DON and are in many cases covered by the same surveys due to the high degree of similiarity. NIV is often detected in much lower concentrations than DON, but is considered to be more toxic. Major sources. Fusarium graminearum is a well known producer of NIV and FX in cereals. In temperate climates F. poae, which is a consistent producer of NIV (Thrane et al., 2004), may be responsible for NIV in cereals. Minor sources. Strains of F. culmorum that produce NIV are less commonly isolated than those that produce DON producers. F. equiseti and F. crookwellense found in some cereal samples and in vegetables may also produce NIV. In potatoes F. venenatum strains that produce NIV have been detected (Nielsen and Thrane, 2001).

T-2 toxin
T-2 toxin is one of the most toxic trichothecenes, whereas the derivative HT-2 toxin is less toxic. Due to structural similarity these toxins are often included in the same analytical method. Major sources. Fusarium sporotrichioides and F. langsethiae, frequently isolated from cereals in Europe, are consistent producers of T-2 and HT-2 (Thrane et al., 2004). Minor sources. Only a few T-2 and HT-2 producing strains of F. poae and F. sambucinum have been found (Nielsen and Thrane, 2001; Thrane et al., 2004).

Diacetoxyscirpenol (DAS)
Diacetoxyscirpenol (DAS) and monoacetylated derivatives (MAS) are a fourth group of important trichothecenes in food. Major sources. Fusarium venenatum isolates often produce high levels of DAS and this species is frequently isolated from cereals and potatoes (Nielsen and Thrane, 2001). F. poae isolates also often produce high levels of DAS. Minor sources. Fusarium equiseti isolates can produce DAS and MAS in high amounts, but this species is infrequently isolated from cereals and vegetables. F. sporotrichioides and F. langsethiae also produce DAS and MAS; however at lower levels (Thrane et al., 2004). F. sambucinum isolates produce DAS and MAS and are a probable cause of DAS in potatoes (Ellner, 2002).

Zearalenone causes hyperoestrogenism in swine and possible effects in humans have also been reported. Derivatives of zearalenone have been used as growth promoters in livestock; however this is now banned in European Union (Launay et al., 2004). The toxicity of zearalenone and its derivatives have been reviewed recently (Hagler et al., 2001). Major sources. Fusarium graminearum and F. culmorum are the most pronounced producers of zearalenone and several derivatives. They occur frequently in cereals all over the world. Recently, F. graminearum has been divided into nine phylogenetic species (O’Donnell et al., 2004); however in the present context this species concept will not be used as a correlation to existing mycotoxicological literature is impossible at this stage.
Minor sources. Under laboratory conditions Fusarium equiseti produces a number of zearalenone derivatives in high amounts, but little is known about production under natural conditions. F. crookwellense also produces zearalenone.

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