In vitro ruminal degradation of ricin and its effect on microbial growth

• Autor(a) principal: Oliveira, M. R. C.
• Data de Publicação: 2010
• Outros Autores: Oliveira, A. S. de, Campos, J. M. S., Lana, R. P., Machado, O. L. T., Retamal, C. A., Detmann, E., Valadares Filho, S. C.
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: https://doi.org/10.1016/j.anifeedsci.2010.01.006; http://www.locus.ufv.br/handle/123456789/21917
• topic: Castorseed; Detoxification; Electrophoresis; Toxin

Ricin is a toxic protein found in castorseed (Ricinus communis L.). We hypothesized that ruminal microbiota are capable of degrading ricin, and that the toxin inhibits ruminal microbial growth. Therefore, first we evaluated the in vitro ruminal degradation of ricin from solvent castorseed meal (SCM) by SDS-PAGE and densitometry analysis of culture medium (Experiment 1). Culture medium (three replicates) were collected after 0, 3, 6, 12, 24 and 48 h of incubation content initially 0, 61, 122 and 244 μg of ricin/mL or 122 μg of ricin/mL (without ruminal inoculum). No protein compounds were detected by SDS-PAGE in the culture medium without ricin, indicating an absence of interference from the ruminal inoculum. Ricin chains remained intact in the absence of rumen inoculum, but they were degraded at rates of 0.2725, 0.1504 and 0.0648 h^−1 with ruminal inoculum, at initial ricin concentrations of 61, 122 and 244 μg/mL. Next, the effect of ricin denaturation on rumen microbial specific growth rate (SGR) (OD-600 nm) and the average ammonia concentration at the same time of incubation were investigated (Experiment 2). This experiment had a completely randomized design in a 3 × 3 factorial (three replicates) arrangement, with three sources of protein (trypticase-control; crude extract of soluble protein at pH 3.8 buffer of solvent castorseed meal (CEP) intact, containing 1.46 mg of ricin/mL; and denatured CEP with calcium oxide, containing 0.04 mg of ricin/mL) and three protein levels (0.42, 0.84, and 1.68 mg/mL). There was interaction (P=0.021) between protein level and protein source for SGR. A linear increase (P<0.001) of SGR was observed with increase of trypticase level, but there was a quadratic effect (P=0.023) with increase of intact CEP level, with a minimum value of SGR of −0.004 h^−1 at a protein level of 1.45 mg/mL (210 μg of ricin/mL) of intact CEP. There was no effect (P=0.099) of denatured CEP level, but SGR increased (P<0.001) 3.2 times with denaturation of intact CEP. Ruminal microbial growth was inhibited by 50% with 89 μg of ricin/mL. Ammonia concentration was 91% lower (P<0.001) for the CEP source when compared to trypticase, but the denaturation of intact CEP had no effect (P=0.9560) on the ammonia concentration. Although ruminal microbiota was able to degrade ricin in in vitro conditions, the toxin inhibits ruminal microbial growth. Therefore, complete detoxification of CSM before using it to feed ruminants is recommended. The denatured CEP presents potential of use as modifier of rumen microbial fermentation.