Metabolism of Melamine by Klebsiella terragena

Abstract

Experiments were conducted to determine the pathway of melamine metabolism by Klebsiella terragena (strain DRS-1) and the effect of added NH 4 ؉ on the rates and extent of melamine metabolism. In the absence of added NH 4 ؉ , 1 mM melamine was metabolized concomitantly with growth. Ammeline, ammelide, cyanuric acid, and NH 4 ؉ accumulated transiently in the culture medium to maximal concentrations of 0.012 mM, 0.39 mM, trace levels, and 0.61 mM, respectively. In separate incubations, in which cells were grown on either ammeline or ammelide (in the absence of NH 4 ؉), ammeline was metabolized without a lag while ammelide metabolism was observed only after 3 h. In the presence of 6 mM added NH 4 ؉ (enriched with 5% 15 N), ammeline, ammelide, and cyanuric acid accumulated transiently to maximal concentrations of 0.002 mM, 0.47 mM, and trace levels, respectively, indicating that the added NH 4 ؉ had little effect on the relative rates of triazine metabolism. These data suggest that the primary mode of melamine metabolism by K. terragena is hydrolytic, resulting in successive deaminations of the triazine ring. Use of 15 N-enriched NH 4 ؉ allowed estimates of rates of triazine-N mineralization and assimilation of NH 4 ؉-N versus triazine-N into biomass. A decrease in the percent 15 N in the external NH 4 ؉ pool, in conjunction with the accumulation of ammelide and/or triazine-derived NH 4 ؉ in the culture medium, suggests that the initial reactions in the melamine metabolic pathway may occur outside the cytoplasmic membrane.

Scientific Opinion on Melamine in Food and Feed

“…Various strains of both species were able to deaminate melamine to ammeline, ammelide and cyanuric acid. Following hydrolytic ring cleavage cyanuric acid was converted into NH 4 + and carbon dioxide; probably via biuret and urea (Jutzi et al, 1982;Shelton et al,1997). Deamination is a common pathway of rumen bacteria and protozoa and hence ruminal biotransformation of melamine can be expected.…”

Effect of Short‐term Exposure of Selected Aromatic Nitrogen Compounds on Wastewater Treatment

“…Bacteria such as Klebsiella terragena strain DRS-1 and Micrococcus sp. strain MF-1 are capable of deaminating melamine successively (Shelton et al, 1997;El-Sayed et al, 2006). Cyanuric acid is further subject to hydrolytic ring cleavage to CO 2 and NH 4 þ via hydrolysis of biuret and allophanate (Cook, 1987;Cheng et al, 2005).…”

Biodegradation of Melamine and Cyanuric Acid by a Newly-Isolated <i>Microbacterium</i> Strain

“…Some melamine-degrading bacterial strains, such as Klebsiella terragena DRS-1 [8], Norcadioides sp. ATD6 [9], Pseudomonas sp.…”