Sialic Acids: An Important Family of Carbohydrates Overlooked in Environmental Biofilms

Abstract

Sialic acids in the structural matrix of biofilms developing in engineered water systems constitute a potential target in the battle against biofouling. This report focuses specifically on the presence of sialic acids as part of the extracellular polymeric substances (EPS) of biofilms forming in cooling towers and the potential effect of nutrient starvation on sialic acid presence and abundance. Two cooling water compositions were compared in parallel pilot-scale cooling towers, one poor in nutrients and one enriched in nutrients. Fresh deposits from the two cooling towers were collected after a five-week operation period. EPS extractions and analyses by Fourier transform infrared spectroscopy (FTIR) and high-resolution mass spectrometry (MS), along with 16S rRNA gene amplicon sequencing were performed. The results of MS analyses showed the presence of pseudaminic/legionaminic acids (Pse/Leg) and 2-keto-3-deoxy-d-glycero-d-galacto-nononic acid (KDN) in both biofilm EPS samples. FTIR measurements showed the characteristic vibration of sialic acid-like compounds ν(C=O)OH in the nutrient poor sample exclusively. Our findings, combined with other recent studies, suggest that bacterial sialic acids are common compounds in environmental biofilms. Additionally, the conservation of sialic acid production pathways under nutrient starvation highlights their importance as constituents of the EPS. Further in-depth studies are necessary to understand the role of sialic acids in the structural cohesion and protection of environmental biofilm layer.

Sialylation and Sulfation of Anionic Glycoconjugates Are Common in the Extracellular Polymeric Substances of Both Aerobic and Anaerobic Granular Sludges

“…The extraction of EPS from both aerobic and anaerobic granules was based on the alkaline heat extraction method described in the previous work. − Aerobic granular sludge was collected from two full-scale wastewater treatment plants (Epe and Zutphen) in the Netherlands, which are operated with the Nereda Technology. EPS was extracted by alkaline extraction as explained in detail by Bahgat et al for the demonstration plants of Epe (sewage) and Zutphen (dairy).…”

“…Anaerobic granular sludge was collected from two full-scale anaerobic granular sludge wastewater treatment systems (treating papermill and brewery wastewaters). The EPS was extracted with alkaline extraction as previously described by Pinel et al 17 In short, the EPS was extracted by adding dried biomass to 0.1 M NaOH at 80 °C (10 g/L). The sample was stirred vigorously for 30 min, after which it was cooled and centrifuged at 3300 g for 30 minutes.…”

Enrichment and application of extracellular nonulosonic acids containing polymers of Accumulibacter

“…Very recently, a mass spectrometry based survey revealed an unexpectedly wide distribution of NulOs among non-pathogenic environmental bacteria (Kleikamp et al 2020). Pinel et al (2020) described the presence of Kdn and bacterial sialic acids in biofilms forming in cooling towers. In wastewater environments, Boleij et al (2020) detected NeuAc, Kdn, and bacterial sialic acids in the extracellular polymeric substances (EPS) of anammox granular sludge.…”