Spectroscopic characterization of extracellular polymeric substances from a mixed culture dominated by ammonia-oxidizing bacteria

Extracellular polymeric substances (EPS) of aerobic (AerAOB) and anaerobic ammonium-oxidizing bacteria (AnAOB) are expected to have a significant impact on the performance of autotrophic nitrogen removal in engineered systems. However, there are a few investigations of the EPS of AerAOB and AnAOB, and the results are contradictory. In this study, photometric measurements indicated that the EPS of AerAOB- (31.74 +/- 1.48 mg/gVSS, volatile suspended solids) and AnAOB-enriched cultures (30.12 +/- 1.52 mg/g-VSS) contained more polysaccharides than did conventional activated sludge from a municipal wastewater treatment facility (10.76 +/- 0.83 mg/g-VSS). In addition, the EPS of the AnAOB-enriched culture was dominated by proteins, leading to a considerably higher protein/polysaccharide ratio (2.64 +/- 0.12) than those of the AerAOB-enriched culture (0.56 +/- 0.03) and conventional activated sludge (1.96 +/- 0.09). Characterization using Fourier transform infrared spectroscopy (FTIR) revealed the dominance of amide bands and/or polysaccharide-associated bands in the EPS of AnAOB and AerAOB. These results corroborate the data from the photometric measurements. In addition, the EPS of AnAOB (23.1% +/- 1.2%) and AerAOB (21.9% +/- 1.1%) had a higher portion of a-helices, which is the key protein secondary structure that determines flocculation or cell aggregation, in the amide I band than that of activated sludge (16.7% +/- 0.8%). X-ray photoelectron spectroscopy (XPS) characterization also revealed significantly different functionalities among the EPS of the three mixed cultures; e.g., O-(C,H), which indicates the presence of polysaccharides, was richer in the EPS of AerAOB, whereas protonated amines, which are commonly found in amino acids and amino sugars, accounted for a large portion of the EPS of AnAOB. The results of this study can potentially expand our knowledge of the microbial aggregates responsible for autotrophic nitrogen removal. (C) 2014 Elsevier Ltd. All rights reserved.