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Sweet mar­ine particles res­ist hungry bac­teria

Feb 19, 2021

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.   

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)

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.

Fast bac­terial com­munity

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. 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. This bac­terial com­munity works so well that the ma­jor part of mi­croalgal sug­ars are de­graded be­fore they ag­greg­ate and start to sink. A large amount of the se­questered car­bon there­fore is re­leased back into the at­mo­sphere.

But, how is it pos­sible that nev­er­the­less a lot of car­bon is still trans­por­ted to the deep-sea? The sci­ent­ists of the group Mar­ine Gly­cobi­o­logy now re­vealed a com­pon­ent that may be in­volved in this pro­cess and pub­lished their res­ults in the journal Nature Communications. “We found a mi­croalgal fucose-con­tain­ing sulph­ated poly­sac­char­ide, in short FCSP, that is res­ist­ant to mi­cro­bial de­grad­a­tion,” says Silvia Vidal-Mel­gosa, first au­thor of the pa­per. “This dis­cov­ery chal­lenges the ex­ist­ing paradigm that poly­sac­char­ides are rap­idly de­graded by bac­teria.” This as­sump­tion is the reason why sug­ars are over­looked as a car­bon sink – un­til now. Ana­lyses of the bac­terial com­munity, which were per­formed by sci­ent­ists from the de­part­ment of Mo­lecu­lar Eco­logy at the MPI in Bre­men and the Uni­versity of Gre­if­swald, showed bac­teria had a low abund­ance of en­zymes for the de­grad­a­tion of this sugar.  

A cru­cial part of the find­ing is that this mi­cro­bial res­ist­ant sugar formed particles. Dur­ing growth and upon death uni­cel­lu­lar di­at­oms re­lease a large amount of un­known, sticky long-chained sug­ars. With in­creas­ing con­cen­tra­tion, these sugar chains stick to­gether and form mo­lecu­lar net­works. Other com­pon­ents at­tach to these small sugar flakes, such as other sugar pieces, di­atom cells or min­er­als. This makes the ag­greg­ates lar­ger and heav­ier and thus they sink faster than single di­atom cells. These particles need about ten days to reach a depth of 1000 meters – of­ten much longer. This means that the sticky sugar core has to res­ist bio­de­grad­a­tion for at least so long to hold the particle to­gether. But this is very dif­fi­cult as the sugar-eat­ing bac­teria are very act­ive and al­ways hungry.

Silvia Vidal-Melgosa at the set up used for the sampling of particulate organic matter by sequential filtration of 100 litre of seawater at Helgoland. The picture shows the collection of one filter where organic matter (in this case matter with molecular sizes between 10 and 3 micrometre) has been retained. (© Max Planck Institute for Marine Microbiology/V. Solanki)
Silvia Vidal-Melgosa at the set up used for the sampling of particulate organic matter by sequential filtration of 100 litre of seawater at Helgoland. The picture shows the collection of one filter where organic matter (in this case matter with molecular sizes between 10 and 3 micrometre) has been retained. (© Max Planck Institute for Marine Microbiology/V. Solanki)
Detail of a filter covered by particulate organic matter (in this case organic matter with molecular sizes greater than 0.7 micrometre) during the phytoplankton spring bloom at Helgoland. (© Max Planck Institute for Marine Microbiology/S. Vidal-Melgosa)
Detail of a filter covered by particulate organic matter (in this case organic matter with molecular sizes greater than 0.7 micrometre) during the phytoplankton spring bloom at Helgoland. (© Max Planck Institute for Marine Microbiology/S. Vidal-Melgosa)

New method to ana­lyse mar­ine sug­ars

In the arrayjet robot, the microarrays were "printed" with the sugar molecules. (© Max Planck Institute for Marine Microbiology/K. Matthes)
In the Arrayjet robot, the microarrays were "printed" with the sugar molecules. (© Max Planck Institute for Marine Microbiology/K. Matthes)

In or­der to un­ravel the struc­tures of mi­croal­gae poly­sac­char­ides and identify res­ist­ant sticky sug­ars, the sci­ent­ists of the re­search group Mar­ine Gly­cobi­o­logy are test­ing new meth­ods. This is ne­ces­sary be­cause mar­ine sug­ars are found within com­plex or­ganic mat­ter mix­tures. In the case of this study, they used a method which ori­gin­ates from med­ical and plant re­search. It com­bines the high-through­put ca­pa­city of mi­croar­rays with the spe­cificity of mono­clonal an­ti­body probes. This means, that the sci­ent­ists ex­trac­ted the sugar-mo­lecules out of the sea­wa­ter samples and in­ser­ted them into a ma­chine that works like a printer, which does­n’t use ink but mo­lecules. The mo­lecules are sep­ar­ately “prin­ted” onto ni­tro­cel­lu­lose pa­per, in form of a mi­croar­ray. A mi­croar­ray is like a mi­cro­chip, small like a fin­ger­nail, but can con­tain hun­dreds of samples. Once the ex­trac­ted mo­lecules are prin­ted onto the ar­ray it is pos­sible to ana­lyse the sug­ars present on them. This is achieved by us­ing the mono­clonal an­ti­body probes. Single an­ti­bod­ies are ad­ded to the ar­rays and as they re­act only with one spe­cific sugar the sci­ent­ists can see, which sug­ars are present in the samples.

“The novel ap­plic­a­tion of this tech­no­logy en­abled us to sim­ul­tan­eously mon­itor the fate of mul­tiple com­plex sugar mo­lecules dur­ing an algal bloom,” says Silvia Vidal-Mel­gosa. “It al­lowed us to find the ac­cu­mu­la­tion of the sugar FCSP, while many other de­tec­ted poly­sac­char­ides were de­graded and did not store car­bon.” This study proves the new ap­plic­a­tion of this method. “Not­ably, com­plex car­bo­hydrates have not been meas­ured in the en­vir­on­ment be­fore at this high mo­lecu­lar res­ol­u­tion,” says Jan-Hendrik Hehem­ann, leader of the group Mar­ine Gly­cobi­o­logy and senior au­thor of the study. “Con­sequently, this is the first en­vir­on­mental gly­comics data­set and there­fore the ref­er­ence for fu­ture stud­ies about mi­cro­bial car­bo­hydrate de­grad­a­tion”.

Next step: Search for particles in the deep sea

The dis­cov­ery of FCSP in di­at­oms, with demon­strated sta­bil­ity and ad­hes­ive prop­er­ties, provides a pre­vi­ously un­char­ac­ter­ised poly­sac­char­ide that con­trib­utes to particle form­a­tion and po­ten­tially there­fore to car­bon se­quest­ra­tion in the ocean. One of the next steps in the re­search is “to find out, if the particles of this sugar ex­ist in the deep ocean,” says Hehem­ann. “That would in­dic­ate that the sugar is stable and con­sti­tutes an im­port­ant player of the bio­lo­gical car­bon pump.” Fur­ther­more, the ob­served sta­bil­ity against bac­terial de­grad­a­tion, and the struc­ture and physi­co­chem­ical be­ha­viour of di­atom FCSP point to­wards spe­cific bio­lo­gical func­tions. “Given its sta­bil­ity against de­grad­a­tion, FCSP, which coats the di­atom cells, may func­tion as a bar­rier pro­tect­ing the cell wall against mi­crobes and their di­gest­ive en­zymes,” says Hehem­ann. And last but not least, an­other open ques­tion to be solved: These sugar particles were found in the North Sea near the is­land of Hel­go­land. Do they also ex­ist in the sea of other re­gions in the world?  

 

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

Par­ti­cip­at­ing in­sti­tu­tions

  • Max Planck Institute for Marine Microbiology, Bremen
  • MARUM - Center for Marine Environmental Sciences at the University of Bremen
  • University of Greifswald, Germany
  • University of Oldenburg, Germany
  • Alfred Wegener Institute for Polar and Marine Research, Germany
  • Newcastle University, United Kingdom

Fund­ing

This study was fun­ded by the Max Planck So­ci­ety and sup­por­ted by the DFG grant HE 7217/​1-1, through the Cluster of Ex­cel­lence “The Ocean Floor - Earth’s Un­charted In­ter­face” pro­ject 390741603 and the DFG re­search unit FOR2406 “POMPU - Pro­teo­ge­n­om­ics of Mar­ine Poly­sac­char­ide Util­iz­a­tion”.

Please dir­ect your quer­ies to:

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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