Irene Lazzaro

Fatty acid esters of fumonisins: first evidence of their presence in maize

Fumonisin derivatives obtained by esterification of fumonisin B1 (FB1) with palmitic, oleic and linoleic fatty acids have been recently described, but never reported in raw maize so far. In this study, the presence of oleoyl-EFB1 (EFB1OA) and linoleoyl-EFB1 (EFB1LA) in raw maize is reported by means of a suitable LC-ESI-MS/MS method. In addition, the production of EFB1 derivatives by three Fusarium verticillioides strains is described on malt extract–based media and on corn meal–based growth media. EFB1OA and EFB1LA were produced by all considered strains in corn meal medium, with EFB1LA > EFB1OA. On the contrary, EFB1OA and EFB1LA were never observed in Fusarium cultures grown on a malt extract medium, suggesting that the esterification of FB1 can occur only in a complex matrix such as maize.

Fumonisins B, A and C profile and masking in Fusarium verticillioides strains on fumonisin-inducing and maize-based media.

The production of fumonisin B, A and C and hidden and partially hydrolysed fumonisin occurrence was investigated in 3 strains of Fusarium verticillioides isolated from maize, cultured for 21-45days on malt extract medium at 25°C and 0.955-0.990 water activity (a(w)). Fumonisin A-B and C series were produced by all the strains in all conditions studied, with B-fumonisin≫C-fumonisin>A-fumonisin following a similar trend. The dynamic of fumonisin production was significantly influenced by factors considered and their interaction, with a(w)=0.990 as favourable condition in ITEM 10026 and ITEM 10027. All fumonisins were maximised at 30days incubation in ITEM 10027 and ITEM 1744 and at 45days incubation in ITEM 10026. Partially hydrolysed fumonisins were detected only for the B-group. Hidden fumonisins were never observed in Fusarium cultures grown on malt extract medium but were detected in the additional trial on maize-based medium, suggesting that the masking phenomenon can occur only in a complex matrix.

Cornmeal and starch influence the dynamic of fumonisin B, A and C production and masking in Fusarium verticillioides and F. proliferatum.

Fusarium verticillioides and F. proliferatum can infect maize ears and produce fumonisins. The fumonisin B (FB) series is the most prolifically produced, followed by fumonisin C (FC), A (FA) and P (FP); moreover hidden forms of fumonisins have been detected in maize and derivatives. There is a lack of information about which maize component may affect fumonisin pattern production. Therefore, in this work we studied the role of cornmeal and corn starch, as the sole source of nutrition, in the production dynamic of all fumonisin series, hidden forms included, in different strains of F. verticillioides and F. proliferatum incubated at 25°C for 7-45days. Both Fusarium species produced high amounts of FB, following the chemotype FB1>FB2>FB3; FC and FA were produced in lesser amounts, showing the chemotypes: FA2+FA3>FA1 and FC1>FC2+FC3>FC4, respectively; while no FP were detected. F. verticillioides was more prolific than F. proliferatum in fumonisin production (ten times more on average) in all the tested conditions. Fumonisin production was higher in cornmeal than in starch based medium in both Fusarium species; FA and FC were detected only in the former medium. An important role of amylopectin as an inducing factor for fumonisin biosynthesis was suggested, as were acid pH conditions. Fumonisin hidden forms may occur in cornmeal medium, whereas they were never found at significant levels in corn starch medium.

FUM and BIK gene expression contribute to describe fumonisin and bikaverin synthesis in Fusarium verticillioides

Fusarium verticillioides is a maize pathogen that produces toxic secondary metabolites, including fumonisins and bikaverin. The regulation of biosynthetic gene expression and the production of these metabolites are not fully understood and in this study we investigated the influence of water activity (0.955 and 0.990) on the expression of 5 genes (FUM3-FUM8-FUM13-FUM14 and BIK1) in F. verticillioides strains after 14 and 21days incubation. Fumonisin production and biosynthetic gene expression were greatest at a(w)=0.990, and the same trend was observed for bikaverin production, and BIK1 expression. FUM3 and FUM14 were the most highly expressed genes and were positively correlated with the production of FB(1), FB(2) and FB(3). When FUM14 is more highly expressed than FUM3 the amount of FB(3) quantified is higher with respect to FB(1); this could be explained by the role of FUM3 in the hydroxylation of FB(3) to FB(1).

Oleoyl and linoleoyl esters of fumonisin B1 are differently produced by Fusarium verticillioides on maize and rice based media

Fatty acid esters of fumonisins, namely oleoyl- and linoleoyl esters of fumonisin B1 (EFB1OA and EFB1LA, respectively), are modified forms of fumonisins whose formation and occurrence have been reported so far in naturally infected maize and in artificially inoculated rice. There is a lack of knowledge about the mechanism of formation, mainly in relation to the role played by the substrate. Therefore, in this work we studied the dynamics of accumulation of the toxin and its esters, together with their precursor, in maize and rice based media inoculated with different strains of F. verticillioides and incubated at 25 °C for 7-45 days. The production pattern of FB1 and its modified forms was significantly influenced by growth media, reaching a higher concentration in cornmeal compared to rice based medium. Similarly, cornmeal was more supportive for the conversion of FB1 by considering the esterification rate, with a prevalence of linoleoyl esters compared to oleoyl esters resembling the OA/LA rate in both media. The conversion of FB1 into fatty acid esters was also shown as strain-related. Results, thus, strongly support the hypothesis that fatty acid esters of FB1 are produced by the fungus itself at a late stage of growth, or at a certain point of FB1 accumulation in the medium, using fatty acids from the substrate.