Abstract
Anaerobic granular sludge is composed of multispecies microbial aggregates embedded in a matrix of extracellular polymeric substances (EPS). Here we characterized the chemical fingerprint of the polysaccharide fraction of EPS in anaerobic granules obtained from full-scale reactors treating different types of wastewater. Nuclear magnetic resonance (NMR) signals of the polysaccharide region from the granules were very complex, likely as a result of the diverse microbial population in the granules. Using nonmetric multidimensional scaling (NMDS), the 1H NMR signals of reference polysaccharides (gellan, xanthan, alginate) and those of the anaerobic granules revealed that there were similarities between the polysaccharides extracted from granules and the reference polysaccharide alginate. Further analysis of the exopolysaccharides from anaerobic granules, and reference polysaccharides using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) revealed that exopolysaccharides from two of the anaerobic granular sludges studied exhibited spectra similar to that of alginate. The presence of sequences related to the synthesis of alginate was confirmed in the metagenomes of the granules. Collectively these results suggest that alginate-like exopolysaccharides are constituents of the EPS matrix in anaerobic granular sludge treating different industrial wastewater. This finding expands the engineered environments where alginate has been found as EPS constituent of microbial aggregates.
Highlights
The capacity of microorganisms to form aggregates has been the key to the development of high-rate wastewater treatment reactors such as the up-flow and expanded anaerobic granular sludge bed (UASB and EGSB) reactors
Since the phenomenon of granulation is independent of aerobic or anaerobic environments and since granulation occurs in reactors treating different types of wastewaters, the following questions were raised: i) is there a common exopolysaccharide in anaerobic granules treating industrial wastewaters, ii) whether alginate-like exopolysaccharides are present in anaerobic granules, and iii) whether the presence of certain exopolysaccharide is linked to a particular microbial community
The aim of this study was to get insight into the chemical fingerprint of the exopolysaccharide fraction of extracellular polymeric substances (EPS) in anaerobic granules obtained from various full-scale reactors using nuclear magnetic resonance (NMR) and MALDI-TOF MS approaches. 16S rRNA amplicon and metagenomic pyrosequencing were further used to characterize the microbial composition of the anaerobic granules and to investigate the presence of genes related to exopolysaccharides metabolism
Summary
The capacity of microorganisms to form aggregates (i.e., granules) has been the key to the development of high-rate wastewater treatment reactors such as the up-flow and expanded anaerobic granular sludge bed (UASB and EGSB) reactors. The main exopolysaccharide of aerobic granules cultivated in a pilot plant treating a mixture of municipal sewage and abattoir wastewater seemed to have a similar chemical structure to seaweed alginate, as revealed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS)[12]. This alginate-like exopolysaccharide was proposed to be responsible for maintaining the gel-like structure of those aerobic granules; the granules microbial community structure was not investigated though. The aim of this study was to get insight into the chemical fingerprint of the exopolysaccharide fraction of EPS in anaerobic granules obtained from various full-scale reactors using NMR and MALDI-TOF MS approaches. 16S rRNA amplicon and metagenomic pyrosequencing were further used to characterize the microbial composition of the anaerobic granules and to investigate the presence of genes related to exopolysaccharides metabolism
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