Revealing Function of Amino Acids in Nitrifying and Anammox Systems Through Chromatography and Metagenomic Analyses

Extracellular polymeric substances (EPS) in nitrifying batch biofilm reactors (SBBRs) and anammox reactors are important for aggregation of autotrophic nitrifying and anammox bacteria. In addition, soluble microbial products (SMP) also play very important roles in biological degradation in these processes. Therefore, more comprehensive analytical methods are required for better characterization of EPS and SMP. Chromatography and metagenomic analyses can help to accelerate the EPS/SMP characterization. Amino acids, esters, dipeptides, and fatty acids are the widespread compounds in both EPS and SMP of all nitrifying and anammox reactors. Heterotrophs of Chlorobi bacterium_OLB7 proliferated in SBBRs and Lautropia sp. SCN_69-89 in the anammox reactors. The metagenomic-based analysis showed that these heterotrophs might grow by assimilating amino acids or peptides in EPS and SMP by possessing amino acids degradation genes. The organics utilization pattern was affected by the addition of organics in SBBRs. Heterotrophs in the SBBR with the addition of organics merely possessed amino acids degradation genes, whereas those in the SBBR without the addition of organics had both amino acids synthesizing and degrading genes. Heterotrophs in the anammox reactors could utilize amino acids or peptides produced by anammox bacteria and other heterotrophs. The clarification of amino acids function can be useful for accelerating the application of autotrophic nitrogen removal systems to better understand microbial aggregation and interactions.