Glucosylation and other biotransformations of T-2 toxin by yeasts of the trichomonascus clade

Abstract

Trichothecenes are sesquiterpenoid toxins produced by Fusarium species. Since these mycotoxins are very stable, there is interest in microbial transformations that can remove toxins from contaminated grain or cereal products. Twenty-three yeast species assigned to the Trichomonascus clade (Saccharomycotina, Ascomycota), including four Trichomonascus species and 19 anamorphic species presently classified in Blastobotrys, were tested for their ability to convert the trichothecene T-2 toxin to less-toxic products. These species gave three types of biotransformations: acetylation to 3-acetyl T-2 toxin, glycosylation to T-2 toxin 3-glucoside, and removal of the isovaleryl group to form neosolaniol. Some species gave more than one type of biotransformation. Three Blastobotrys species converted T-2 toxin into T-2 toxin 3-glucoside, a compound that has been identified as a masked mycotoxin in Fusarium-infected grain. This is the first report of a microbial whole-cell method for producing trichothecene glycosides, and the potential large-scale availability of T-2 toxin 3-glucoside will facilitate toxicity testing and development of methods for detection of this compound in agricultural and other products.

Fig 1

Chemical structures of T-2 toxin, 3-acetyl T-2 toxin, neosolaniol, T-2 toxin 3-glucoside, HT-2 toxin, T-2 triol, 4-deoxy T-2 toxin, and T-2 tetraol.

Fig 2

Representative GC/MS traces of culture extracts from feeding experiments on G-YNB. Time (in minutes) is shown on the x axes, and total ion current intensity is shown on the y axes of the graphs. (A) B. muscicola culture immediately after T-2 toxin was added, (B) B. capitulata culture 6 days after the culture was fed T-2 toxin; (C) B. parvus culture 6 days after the culture was fed T-2 toxin; (D) B. muscicola culture 6 days after the culture was fed T-2 toxin. 8-Bu, 8-butyryl.

Fig 3

Time course (in days) of T-2 toxin metabolism by cultures of B. muscicola (diamonds), B. robertii (triangles), and B. peoriensis (squares) grown on G-YNB and cultures of B. muscicola grown on YNB (glucose-free medium) (circles) as measured by GC/MS. The graph shows average T-2 toxin concentrations ± standard deviations (error bars) from three cultures.

Fig 4

MALDI-TOF MS analysis. (A) T-2 toxin; (B) T-2 toxin 3-glucoside in B. muscicola culture extracted 6 days after the culture was fed T-2 toxin.

Fig 5

Analysis of sugar residues from T-2 toxin 3-glucoside.

Fig 6

Structure of T-2 toxin 3-glucoside with the carbons numbered.

Fig 7

Phylogenetic relationships among species of Trichomonascus and its anamorphic genus Blastobotrys on the basis of maximum parsimony analysis of D1/D2 large-subunit (LSU) rRNA gene sequences; the phylogenetic tree was modified from that of Kurtzman and Robnett (27). Bootstrap values are for 1,000 replicates. The NRRL strain designations are shown. Type strains and isotype strains are indicated by superscript letters T and I, respectively, after the strain designation. GenBank accession numbers for the sequences analyzed are shown after slashes after the strains. Bioconversion of T-2 toxin is shown as follows: acetylation (black circle); glucosylation (black triangle); removal of isovaleryl (black square); no conversion (white square).