Effect of nitroethane and nitroethanol on the production of indole and 3-methylindole (skatole) from bacteria in swine feces by gas chromatography

Authors: Beier, Ross; Anderson, Robin; Krueger, Nathan; Edrington, Thomas; Callaway, Todd; Nisbet, David

Submitted to: Journal of Environmental Science and Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2009
Publication Date: 8/1/2009
Citation: Beier, R.C., Anderson, R.C., Krueger, N.A., Edrington, T.S., Callaway, T.R., Nisbet, D.J. 2009. Effect of nitroethane and nitroethanol on the production of indole and 3-methylindole (skatole) from bacteria in swine feces by gas chromatography. Journal of Environmental Science and Health Part B. 44:613-620.

Interpretive Summary: Indole and 3-methylindole (skatole) are chemicals that cause odor pollution in livestock waste. Skatole can also cause lung damage in horses, rats, and mice, and is also toxic to human lung cells. Skatole can be produced from bacteria in swine feces from the amino acid L-tryptophan. Here, we studied the effect of the addition of two chemicals, nitroethane and nitroethanol, on the microbial production of indole and skatole in swine feces with and without added L-tryptophan. To help determine the amounts of indole and skatole, we modified an existing gas chromatographic method resulting in an improved response for indole and skatole of 236% and 207%, respectively. Nitroethane and nitroethanol addition to swine feces resulted in a decrease in production of skatole and increased the indole levels at 24 h. The elevated levels of indole most likely resulted from inhibition of skatole production. Even though the addition of these compounds did not eliminate the production of skatole in the presence of L-tryptophane, nitroethane decreased the production of skatole (P = 0.02) after 6 h incubation. The addition of the appropriate inhibitors to waste-holding reservoirs may be useful in decreasing the bacterial production of skatole, and this is important because it may be beneficial to farm workers.

Technical Abstract: Indole and 3-methylindole (skatole) are odor pollutants in livestock waste, and skatole is a major component of boar taint in meat. Skatole causes pulmonary edema and emphysema in ruminants and is an olfactory epithelial toxin in rats. Skatole causes bronchiolitis in horses, rats, and mice by damaging lung Clara cells, and is also toxic to human bronchial epithelial cells. Here, we studied the effect of the addition of nitroethane and nitroethanol at 21.8 mM in swine feces on the microbial production of indole and skatole from added L-tryptophan. To facilitate quantification of indole and skatole, we modified a gas chromatographic method that used a nitrogen–phosphorus detector resulting in an improved flame ionization detection response for indole and skatole of 236% and 207%, respectively, eliminating the need for a nitrogen–phosphorus detector. A 10 ppm spike of indole and skatole in water and swine feces resulted in recovery of 78.5 and 96% in water and 76.1 and 85.8% in feces, respectively. The nitroethanol effect on L-tryptophan metabolism after 6 and 24 h incubation resulted in –8.2 and +72.2% change in indole and –41.2 and –8.8% change in skatole production, respectively. Even though the addition of these compounds did not eliminate the production of skatole, nitroethane decreased the production of skatole (P = 0.02) after 6 h incubation. However, at 24 h there was no statistical difference in production. The addition of the appropriate inhibitors to waste-holding reservoirs may be useful in decreasing the bacterial production of skatole.