Decorating the Anammox House: Sialic Acids and Sulfated Glycosaminoglycans in the Extracellular Polymeric Substances of Anammox Granular Sludge

Anammox (anaerobic ammonium oxidation) bacteria are important for
the nitrogen cycle in both natural environments and wastewater treatment
plants. These bacteria have a strong tendency to grow in aggregates
like biofilms and granular sludge. To understand the formation of
anammox aggregates, it is required to unravel the composition of the
extracellular polymeric substances (EPS), which are produced by the
bacteria to develop into aggregates and granules. Here, we investigated
anionic polymers in anammox granular sludge, focussing on sialic acids
and sulfated glycosaminoglycans. Quantification assays and fluorescent
stains indicated that sialic acids and sulfated glycosaminoglycans
were present in the anammox EPS (1.6% equivalents of sialic acids
and 2.4% equivalents of sulfated glycosaminoglycans). Additionally,
the potential genes for the biosynthesis of sialic acids and sulfated
glycosaminoglycans were analyzed in the anammox draft genomes. The
finding of these components in anammox granular sludge and previously
in other nonpathogenic bacteria pointed out that sialic acids and
sulfated glycosaminoglycans are worth investigating in the context
of a broader function in microbial communities and biofilm systems
in general.