Fusarium moniliforme Sheld. A fungus producing a broad spectrum of bioactive metabolites

The phytotoxicity ofFusarium metabolites: An update since 1989

The present article summarises the published phytotoxic effects of severalFusarium metabolites (mycotoxins, phytotoxins, antibiotics and pigments) since 1989. The phytotoxicity of many of the commonly isolated metabolites cannot be disputed, but their role in pathogenesis ofFusarium-induced plant diseases is uncertain. Plant species/varieties differ in their susceptibililty resistance to these toxinsin vitro, as well as toFusarium pathogens under field conditions. Such variations in plant response may reflect resistance mechanisms that operate at several levels, including an initial ability to prevent fungal invasion; prevention of fungal spread and toxin tolerance or degradation. Little is known about the mode of action of most of these metabolites on either animal or plant cells. Several novelFusarium metabolites have been isolated in the past few years. Many are toxic to animals and cell lines, but assessment of their phytotoxicity has largely been neglected. Since many plant pathogenic Fusaria produce a plethora of metabolites, the additive or synergistic actions of toxins in combination must be considered in plant pathology.

Leishmaniasis phytotherapy. Nature's leadership against an ancient disease

The use of phytotherapy to treat human diseases has its roots in pre-historical times. Despite the modern advances achieved in the field of synthetic chemistry, the most efficient drugs available have their genesis directly or indirectly related with the vegetal kingdom. Indigenous communities have long used plant extracts to treat illnesses. Many of these extracts have shown effective action, with new bioactive compounds being extracted and screened every year. These extracts have also proven to be good sources of therapeutic agents to the treatment of Leishmaniasis. This work highlights some of these agents, while trying to emphasize the importance of plants as a source of new and powerful drugs against this widespread disease.

Fumonisins, mycotoxins of increasing importance: their nature and their effects

The fumonisins (FBs) are a group of closely related mycotoxins that are prevalent in maize. They were isolated from strains of Fusarium moniliforme (Sheldon), which were implicated in the aetiology of human oesophageal cancer in the Transkei, South Africa. Their discovery explained the cause of equine encephalomalacia, or "hole in the head" syndrome, when it was found by feeding trials in horses that they elicited the disease. Subsequently, they were found to cause hepatic cancer in rats and pulmonary oedema in pigs, with most animal species tested showing liver and kidney damage. FB1 is the most important of the group and, although poorly absorbed from the gastrointestinal tract, its action is at the cellular level, affecting sphingolipid metabolism. Ceramides derived from sphingosine metabolism are cell regulatory factors affecting, among other things, DNA synthesis. Because FB1 has a close molecular resemblance to sphinganine, it interferes with ceramide biosynthesis and, hence, the processes that it regulates, which is thought to explain its carcinogenic properties. Studies on the FBs are still at a relatively early stage, but it is already clear that they play an important role in animal mycotoxicoses and, by implication, in human disease. A more positive aspect is that they will be used in elucidating the role of sphingolipids in cellular regulation.

Genetic variability in Gibberella fujikuroi and some related species of the genus Fusarium based on random amplification of polymorphic DNA (RAPD)

One of the most important rice pathogens is Fusarium moniliforme (perfect stage: Gibberella fujikuroi), the causal agent of the super-elongation ("bakanae") disease. Thirty-seven strains of this species from different geographical regions were analyzed for their ability to produce gibberellins (GA) and for genetic relatedness by random amplified polymorphic DNA (RAPD). All GA-producing isolates showed nearly identical RAPD patterns using 51 oligonucleotide nona- and deca-mers as arbitrary primers. On the other hand, large differences between GA-nonproducing isolates were obtained. Comparison of the RAPD patterns with those of the tester strains of the six known mating populations (A, B, C, D, E, F) of G. fujikuroi showed that all producer strains belong to mating population C and all nonproducer isolates to other mating populations. Evidence for the usefulness of the RAPD technique to distinguish between mating populations was provided by sexual crossings. Consensus phylogenetic trees based on RAPDs were constructed by the Phylogenetic Analysis Using Parsimony (PAUP) system. In combination with morphological analysis, RAPD can distinguish between different species of the genus Fusarium. These investigations may find an application in the diagnosis of unknown Fusarium spp. and in distinguishing isolates of G. fujikuroi within the section Liseola.

Fumonisins

Fusarium moniliforme Sheldon is a common fungal contaminant of corn and produces a variety of mycotoxins. Among these are the recently discovered fumonisins, which are now known to cause certain animal diseases, namely leukoencephalomalacia in horses and pulmonary edema in swine. There is a significant association between their presence in corn and human esophageal cancer in southern Africa. Fumonisin B1 causes liver cancer in rats. Five other fumonisins--B2, B3, B4, A1 and A2, have been isolated; the last two are N-acetates of fumonisins B1 and B2 and do not appear to be toxic. Several other Fusarium species are now known to produce fumonisins. Procedures for detection and determination of fumonisins include thin layer chromatography, liquid chromatography (with fluorescence derivatization), post-hydrolysis gas chromatography, immunochemical assay, and mass spectrometry. In addition to their natural occurrence in corn-based animal feeds and in home-grown African corn used for food, fumonisins are frequently found in commercial corn-based foods. Fumonisins are moderately heat-stable. No effective detoxification process has yet been developed for use with fumonisin-contaminated feeds.

Obtaining mutants for protoplast fusion of gibberellin-forming Gibberella fujikuroi strains

Auxotrophic, drug-resistant, nitrate-nonutilizing, and albino mutants have been isolated in Gibberella fujikuroi following UV mutagenesis. Protoplasts of complementing auxotrophic strains, mutants with resistance markers, or mutants blocked in different steps of the nitrate assimilatory pathway have been fused to form heterokaryons, diploids, or recombinant haploids. The properties of fusant strains, including gibberellic acid productivity, have been examined and compared to parent strains.

Differential cytotoxicity and mycotoxin content among isolates of Fusarium moniliforme

Ten different isolates of the common corn fungus, Fusarium moniliforme, were cultured on corn, and the production by the isolates of two important mycotoxins, fusarin C and fumonisin B1, was compared. Additionally, both aqueous and organic extracts of the cultures were tested for cytotoxicity to rat primary hepatocytes by measuring the effects of three dose levels on the ability of the cells to take up valine and to cause the release of the cytoplasmic enzyme, lactate dehydrogenase. The fungal isolates differed drastically in their ability to produce the two mycotoxins and in their cytotoxicity. However the toxic effects could not be accounted for by the content of the two toxins measured. Therefore it appears that there are other toxins, both organic and aqueous soluble compounds, that are toxic to liver cells.