Biocatalytic quantification of α‐glucan in marine particulate organic matter

• Published in: MicrobiologyOpen (Weinheim) 2022-06, Vol.11 (3), p.e1289-n/a
• Main Authors: Steinke, Nicola, Vidal‐Melgosa, Silvia, Schultz‐Johansen, Mikkel, Hehemann, Jan‐Hendrik
• Format: Article
• Language: English
• Subjects: Acids; Algae; Animals; Aquatic plants; Bacteria; beta-Glucans; Carbon; Carbon cycle; Carbon dioxide; Chemical reactions; enzymatic hydrolysis; Enzymes; Glucan; Glucans; Glucose; Glycan; Hydrolysis; Laminarin; Marine microorganisms; marine particulate organic matter; Oceans; Oceans and Seas; Organic matter; Original; Particulate Matter; Particulate organic matter; Polysaccharides; quantification; Seawater; Side reactions; β-Glucan
• ISSN: 2045-8827; 2045-8827
• DOI: 10.1002/mbo3.1289

Marine algae drive the marine carbon cycle, converting carbon dioxide into organic material. A major component of this produced biomass is a variety of glycans. Marine α‐glucans include a range of storage glycans from red and green algae, bacteria, fungi, and animals. Although these compounds are likely to account for a high amount of the carbon stored in the oceans they have not been quantified in marine samples so far. Here we present a method to extract and quantify α‐glucans (and compare it with the β‐glucan laminarin) in particulate organic matter from algal cultures and environmental samples using sequential physicochemical extraction and enzymes as α‐glucan‐specific probes. This enzymatic assay is more specific and less susceptible to side reactions than chemical hydrolysis. Using HPAEC‐PAD to detect the hydrolysis products allows for a glycan quantification in particulate marine samples down to a concentration of ≈2 µg/L. We measured glucans in three cultured microalgae as well as in marine particulate organic matter from the North Sea and western North Atlantic Ocean. While the β‐glucan laminarin from diatoms and brown algae is an essential component of marine carbon turnover, our results further indicate the significant contribution of starch‐like α‐glucans to marine particulate organic matter. Henceforth, the combination of glycan‐linkage‐specific enzymes and chromatographic hydrolysis product detection can provide a powerful tool in the exploration of marine glycans and their role in the global carbon cycle. α‐Glucans can be quantified alongside laminarin in marine particulate organic matter samples using structure‐specific hydrolytic enzymes in combination with glucose detection by high‐performance anion‐exchange chromatography and pulsed amperometric detection. This enzymatic method is a new tool for the characterization and quantification of specific algal glycans in the ocean, which is important to understanding microbial carbon cycling and carbon sequestration in the marine environment.