Study on characteristic and mechanism involved in the formation of N- nitrosodimethylamine precursors during microbial metabolism of amino acids

Amino acid metabolism by microorganisms is a new but important pathway for the formation of NDMA precursors in water. We investigated the properties of nitrosamine precursors produced through microbial metabolism of amino acids by polarity rapid assessment method and molecular weight fractionation by ultrafiltration method. The PRAM results showed that the positively charged fraction and the non-polar fraction accounted for most (45 %-79 % and 6 %-82 %, respectively) of the NDMA precursors. The MW fractionation results also indicate the dominant precursors had MWs <1 kDa or over 10 kDa. NDMA precursors produced through amino acid metabolism were identified and quantified. Dimethylamine, N-methyl-alanine and alanine methyl ester were produced during the metabolism of ala-nine and peptone. Together, N-methyl-alanine and dimethylamine averagely contributed 24 % (12 %-44 %) of the NDMA precursors in the alanine medium. The NDMA precursor formation pathway during alanine metabolism in-volves the methylation of alanine to form N-methyl-alanine and the decomposition of alanine anabolism products to form dimethylamine. Nitrosamine precursors are generally formed through anabolism or methylation, but biogenic amines or NH3 can be produced through catabolism before nitrosamine precursor synthesis. Microbial community analysis was performed and Ralstonia was found to be a likely key genus contributing to NDMA precursor formation during alanine metabolism.

Automated summary

Amino acid metabolism by microorganisms is an important pathway for the formation of nitrosamine (NDMA) precursors in water. Through rapid assessment and molecular weight fractionation methods, it was found that positively charged and non-polar fractions were the main contributors to NDMA precursor formation. The dominant precursors had molecular weights below 1 kDa or over 10 kDa. Specific NDMA precursors, such as dimethylamine, N-methyl-alanine, and alanine methyl ester, were produced during alanine and peptone metabolism. The formation of NDMA precursors during alanine metabolism involved methylation of alanine to form N-methyl-alanine and decomposition of alanine metabolites to form dimethylamine. Ralstonia was identified as a key genus contributing to NDMA precursor formation during alanine metabolism.