Aplication of mathematical models for the interaction between S. cerevisiae and zearalenone

PEREYRA C.M.; CAVAGLIERI L.R.; GONZÁLEZ PEREYRA M.L.; DALCERO A.M.; CHIACCHIERA S.M.

Carlos Paz, Córdoba, Argentina

Congreso; Congreso de la Sociedad Argentina de Microbiologia General; 2009

Sociedad Argentina de Microbiologia General

In the latter years, mycotoxin contamination of animal feeds has turned an issue of global concern. Zearalenone (ZEA) is a toxin frequently detected in feedstuffs and cereals. The use of biological sorbents such as yeast cell walls (YCW) added to feed is an option to diminish bioavailability of the toxin in the gastrointestinal tract and the detrimental effects of ZEA mycotoxicosis on productive parameters (CAST, 2003). The aim of this study was to apply 3 mathematical models (Hill, Langmuir y Frumkin-Fowler-Guggenheim) to explain the interaction between ZEA and a commercial preparation of S. cerevisiae YCW by using adsorption isotherms. Interaction assays between ZEA and YCW were performed at pH 2 and pH 6 at 37°C. An aliquot of 500 µL (10 µg/mL) YCW was added to each Eppendorf tube containing 500 µL of 0.5; 5; 10; 20 and 50 µg/mL ZEA solution. Tubes were centrifuged for 30 min at low rpm and 10 min at 1400 rpm to obtain a pellet composed by the toxin which was bound to YCW and a supernatant where free (not bound) toxin was present. The supernatant was separated, evaporated to dryness under N2 stream and analyzed by HPLC using the methodology described by Cerveró et al. (2007). Assays were done in duplicates. At pH 2 the interaction could be explained using the Hill model with an N value of approximately 1. In these conditions, since there was no cooperativity, Langmuir model could also be applied. The adsorption ability of S. cerevisiae YCW according to Hill model (R2=0.998) was 0.18 and the adsorption constant was 0.40 x 10-6 M-1. For Langmuir model (R2=0.997) adsorption ability was 0.14 (g/g) and the adsorption constant was 0.74 x 10-6 M-1. Since the isotherm showed cooperative effect at pH 6, Hill (R2=0.997) and Frumkin-Fowler-Guggenheim (R2=0.996) models were applied. Both models showed identical adsorption ability (0.09 g/g) while ZEA affinity measured by the association constant (b) was higher when using Hill model (2.00 x 10-6 M-1) than when Frumkin-Fowler-Guggenheim model (0.29 x 10-6 M-1) was applied. The adjustment of the 3 methods is comparable (R2). However, Hill model seemed to represent best the adsorption at both pH 2 and 6. Hill model can be applied to sigmoid-shaped as well as to L type isotherms. Its mathematical expression includes the dissociation constant KD, the maximum adsorption ability Gmax and the minimum number of binding sites necessary for cooperative adsorption. The inverse of KD is precisely the adsorption constant we have stated as b. The application of this model is the most useful to explain the interaction between ZEA and YCW, since more information on the mechanisms involved in the interaction can be obtained.