Analysis of marine sugars

Coscinodiscus wailesii is a microalgae belonging to the diatoms, which form algal blooms and produce substantial amounts of polysaccharides in energy stores, cell walls and as exudates. The research group Marine Glycobiology studies the turnover and role of these glycans in the carbon cycle. (© Max Planck Institute for Marine Microbiology/ C. Robb)
Coscinodiscus wailesii is a microalgae belonging to the diatoms, which form algal blooms and produce substantial amounts of polysaccharides in energy stores, cell walls and as exudates. The research group Marine Glycobiology studies the turnover and role of these glycans in the carbon cycle. (© Max Planck Institute for Marine Microbiology/ C. Robb)

Why do we analyse sugars in marine research?

A ma­jor path­way for car­bon se­quest­ra­tion in the ocean is the growth, ag­greg­a­tion and sink­ing of phyto­plank­ton – uni­cel­lu­lar mi­croal­gae like di­at­oms. Just like plants on land, phyto­plank­ton se­quester car­bon from at­mo­spheric car­bon di­ox­ide. When al­gae cells ag­greg­ate, they sink and take the se­questered car­bon with them to the ocean floor. This so called bio­lo­gical car­bon pump ac­counts for about 70 per cent of the an­nual global car­bon ex­port to the deep ocean. Es­tim­ated 25 to 40 per cent of car­bon di­ox­ide from fossil fuel burn­ing emit­ted by hu­mans may have been trans­por­ted by this pro­cess from the at­mo­sphere to depths be­low 1000 meter, where car­bon can be stored for mil­len­nia.

Yet, even it is very im­port­ant, it is still poorly un­der­stood how the car­bon pump pro­cess works at the mo­lecu­lar level. Sci­ent­ists of the re­search group Mar­ine Gly­cobi­o­logy, which is loc­ated at the Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy and the MARUM – Cen­ter for Mar­ine En­vir­on­mental Sci­ences at the Uni­versity of Bre­men, in­vest­ig­ate in this con­text mar­ine poly­sac­char­ides – mean­ing com­pounds made of mul­tiple sugar units – which are pro­duced by mi­croal­gae. These mar­ine sug­ars are very dif­fer­ent on a struc­tural level and be­long to the most com­plex bio­molecules found in nature. In the ocean microalgae produce a lot of sugar during algae blooms. These enormous quantities of algal biomass are normally recycled rapidly by marine bacteria. Especially sugars have been considered as easily digestible and therefore poor candidates for natural carbon sequestration. Now, new research results show: There exists a sugar in algae that resists rapid microbial degradation.

Thus – ac­cord­ing to the hy­po­thesis of the research group – poly­sac­char­ides could also be re­spons­ible for a more rapid move­ment of car­bon-rich ma­ter­ial in the ocean, much like the move­ment of food in hu­mans. There­fore, they could help with the stor­age of car­bon in the depths of the ocean and in the mar­ine sed­i­ment.

How are algal sugars analysed?

These mar­ine sug­ars are very dif­fer­ent on a struc­tural level and be­long to the most com­plex bio­molecules found in nature. One single bac­terium is not cap­able to pro­cess this com­plex sugar-mix. There­fore a whole bunch of meta­bolic path­ways and en­zymes is needed. In nature, this is achieved by a com­munity of dif­fer­ent bac­teria that work closely and very ef­fi­ciently to­gether – a per­fect co­ordin­ated team. 

In order to find microbially resistant sugars, the Bremen scientists have sought out a competent teacher: The sugar-degrading bacteria. These bac­teria have found ways of find­ing poly­sac­char­ides and us­ing them as food. They im­ple­ment pro­teins to cap­ture poly­sac­char­ides and en­zymes to di­gest them. We are in­vest­ig­at­ing how bac­teria re­cog­nize poly­sac­char­ides and how their en­zymes work. Every bac­terium has its very own en­zymes – its own tools – in or­der to cut poly­sac­char­ides. The bac­terial en­zymes are re­spons­ible for the break­ing down of sugar com­pounds – they break the large, com­plex poly­sac­char­ides into small, simple mono­sac­char­ide units. These simple sug­ars are easier to meas­ure than poly­sac­char­ides.

By meas­ur­ing simple sug­ars, much like in a dia­betes blood sugar test, it is possible to quantify poly­sac­char­ides. Thanks to this ap­proach, it is now pos­sible to meas­ure which sug­ars are most com­mon, which sink into the depths and thus act as a fiber in the ocean. This, in turn, al­lows con­clu­sions to be drawn about the role of poly­sac­char­ides in the car­bon cycle.

Which devices are needed for the analysis of marine sugars?

Because sugar analysis involves complex procedures, several different devices and techniques are used. Here we present the most important ones.

Algal cultivation

To analyse the sugars of microalgae, the algal bloom off the coast of Helgoland is regularly sampled. We also cultivate microalgae at the Institute in order to find out which species of algae produce which polysaccharides.

High performance liquid chromatography

High performance liquid chromatography (HPLC) plays an important role in the analysis of algal sugars. Liquid chromatography is a technique used to separate a mixture of substances based on interactions with the solid stationary phase and the mobile phase, which contains the liquid to be separated. The principle of this form of analysis or separation is explained here. In sugar analysis, either enzymes or hydrochloric acid are first used to break the marine polysaccharides into smaller fragments. These fragments can then be separated by HPLC based on their size and structure and identified with the respective standards.

This process uses the enzymes of sugar-eating bacteria, which are produced in large quantities in genetically modified bacteria. Once the exact functioning of the enzymes is determined using enzyme assays and X-ray structure analysis (see below), they can be used to break down the polysaccharides into monosaccharides, which are much easier to analyse. In contrast to hydrochloric acid, the enzymes allow very specific fragments to be produced. This procedure can be used to determine how the individual monosaccharides are linked (because enzymes can usually recognize and cleave only certain compounds) and in which proportions the different monosaccharides are present in the original sample.

3D structure of an enzyme with its sugar substrate - enzyme substrate manno-oligosaccharide captured in the active site of the mutant alpha-mannanase GH76. (©Max Planck Institute for Marine Microbiology, V. Solanki)
3D structure of an enzyme with its sugar substrate - enzyme substrate manno-oligosaccharide captured in the active site of the mutant alpha-mannanase GH76. (©Max Planck Institute for Marine Microbiology, V. Solanki)

Micro-Arrays

This method originally comes from medical and plant research. It combines the high throughput capacity of micro-arrays with the accuracy of monoclonal antibodies. The scientists first extract the sugar molecules from the seawater samples and then feed them into a machine that works a bit like a printer. This “printer” essentially “prints” the polysaccharides onto nitrocellulose paper, the micro-array. A micro-array is similar to a microchip; even though it is only the size of a fingernail, it can contain hundreds of samples. Monoclonal antibodies are added to the sugar molecules on the micro-array. Because the individual antibodies react with only one specific sugar, the researchers can see which monosaccharides are present in the sample.

X-ray structure analysis

The enzymes produced in large quantities are extracted from the bacteria and separated using several liquid chromatography techniques (e.g. IEX, IMAC) until only minimal quantities of other enzymes and salts are present. The enzymes are then mixed with liquids that slowly strip the water from the enzymes, forcing them into a crystalline form. The crystals formed are then removed from the liquid, flash-frozen with liquid nitrogen, and sent to a partner laboratory, where they irradiated with X-rays. This method allows the scientists to look deep inside the enzymes and gain insights into the structure and function.

They can find not only enzymes that cut up the polysaccharides but also those that only bind and hold on to these polysaccharides and function similar to antibodies.

Example projects

This Airyscan super-resolution image shows that fucose-containing sulphated polysaccharide, or FCSP, (in green) occurred around the cells of the chain-forming diatom Chaetoceros socialis and their spines. DAPI (blue) and diatom auto fluorescence (red). Sample collected during the 2016 spring diatom bloom period in Helgoland. (© Max Planck Institute for Marine Microbiology/S. Vidal-Melgosa)
This Airyscan super-resolution image shows that fucose-containing sulphated polysaccharide, or FCSP, (in green) occurred around the cells of the chain-forming diatom Chaetoceros socialis and their spines. DAPI (blue) and diatom auto fluorescence (red). Sample collected during the 2016 spring diatom bloom period in Helgoland. (© Max Planck Institute for Marine Microbiology/S. Vidal-Melgosa)

Sweet mar­ine particles res­ist hungry bac­teria

Rather sweet than salty: In the ocean microalgae produce a lot of sugar during algae blooms. These enormous quantities of algal biomass are normally recycled rapidly by marine bacteria – a degradation process that is an important part of the global carbon cycle. Especially sugars have been considered as easily digestible and therefore poor candidates for natural carbon sequestration. Now scientists from Bremen revealed: There exists a sugar in algae that resists rapid microbial degradation, accumulates, aggregates into particles and stores carbon during spring blooms. With this finding, published in the scientific journal Nature Communications, they show that this sugar can potentially act as an important carbon sink.   

Read more in the press release "Sweet marine particles resist hungry bacteria"

 

Original publication:

Silvia Vidal-Mel­gosa, An­dreas Sich­ert, T. Ben Fran­cis, Daniel Bar­tosik, Jutta Nigge­mann, Antje Wichels, Wil­liam G.T. Wil­lats, Bernhard M. Fuchs, Hanno Teel­ing, Dörte Becher, Thomas Schweder, Rudolf Amann, Jan-Hendrik Hehem­ann: Diatom fucan polysaccharide precipitates carbon during algal blooms. Nature Com­mu­nic­a­tions, Feb­ru­ary 2021

DOI: 10.1038/s41467-021-21009-6

The brown algae Fucus vesiculosus grows on stones almost everywhere along the North Sea and Baltic Sea. For the study the researchers also examined fucoidan of these algae like those at the coast of Heligoland. (© Max Planck Institute for Marine Microbiology, M. Schultz-Johansen)
The brown algae Fucus vesiculosus grows on stones almost everywhere along the North Sea and Baltic Sea. For the study the researchers also examined fucoidan of these algae like those at the coast of Heligoland. (© Max Planck Institute for Marine Microbiology, M. Schultz-Johansen)

Sugar turns brown al­gae into good car­bon stores

Brown algae are important players in the global carbon cycle by fixing large amounts of carbon dioxide and thus extracting this greenhouse gas from the atmosphere. Moreover, because microbial decomposition of dead brown algae is slower than that of other marine plants, carbon dioxide fixed by brown algae remains much longer in the sea. Scientists from the Max Planck Institute for Marine Microbiology, the MARUM – Center for Marine Environmental Sciences at the University of Bremen and other institutes therefore explored why brown algae degrade so slowly. They found that only highly specialized bacteria can carry out the degradation with the help of more than hundred enzymes.  

 

Read more in the press release "Sugar turns brown algae into good carbon stores"

 

Original Publication:

An­dreas Sich­ert#, Chris­topher H. Corz­ett#, Mat­thew S. Schechter, Frank Un­fried, Stephanie Mark­ert, Dörte Becher, Ant­o­nio Fernan­dez-Guerra, Manuel Liebeke, Thomas Schweder, Mar­tin F. Polz, Jan-Hendrik Hehem­ann: Verrucomicrobia use hundreds of enzymes to digest the algal polysaccharide fucoidan. Nature Mi­cro­bi­o­logy, May 2020

DOI: 10.1038/s41564-020-0720-2

# both au­thors con­trib­uted equally

Contact

Group leader

MARUM MPG Bridge Group Marine Glycobiology

Dr. Jan-Hendrik Hehemann

MPI for Marine Microbiology
Celsiusstr. 1
D-28359 Bremen
Germany

Room: 

2126

Phone: 

+49 421 2028-7360

Dr. Jan-Hendrik Hehemann
 
 
 
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