Analysis of marine sugars

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.

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.

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