Something old, something new in the Ocean`s Blue

Whilst the uni­cel­lu­lar al­gae, also known as phyto­plank­ton, con­vert CO₂ into bio­mass, other mi­croor­gan­isms come onto ac­tion when the al­gae ex­crete the fixed car­bon - either dur­ing their life, or when they die - some­times in mass, as after the so-called al­gae bloom. Even in sur­face wa­ter, single-cell or­gan­isms pro­cess many thou­sands of tons of al­gae bio­mass: a cent­ral pro­cess in the mar­ine life cycle. One of the most im­port­ant com­pounds in the ocean is glycolic acid, a dir­ect by-product of pho­to­syn­thesis that is partly con­ver­ted back into CO₂ by mar­ine bac­teria. But here, the pic­ture be­comes blurred - the ex­act fate of the car­bon in glycolic acid was un­known so far.

IIn or­der to come to gain a use­ful as­sess­ment of the global car­bon cycle, however, the equa­tion must not have too many un­knowns.  As we know today, too much CO₂ in­flu­ences life in the ocean. In­creased con­cen­tra­tions of CO₂ in sea­wa­ter acid­ify the oceans, dis­turb the bal­ance between phyto­plank­ton and mi­croor­gan­isms and ul­ti­mately in­flu­ence global cli­mate. In or­der to un­der­stand the con­sequences for cli­mate change on a global scale, a pre­cise know­ledge of the bac­terial de­grad­a­tion of al­gae bio­mass is in­dis­pens­able. For this, however, we need pre­cise ba­sic know­ledge of the loc­a­tion, rate and ex­tent of nu­tri­ent net­works in the ocean. So what ex­actly is the fate of the glycolic acid`s car­bon, which glob­ally means sub­stance quant­it­ies in the range of one bil­lion tons per year?

The forgotten pathway

Re­search­ers do not al­ways have to start from scratch - some­times there are already known puzzle pieces, they just have to be re­cog­nized and placed cor­rectly. One such piece is the β-hy­droxy­as­part­ate cycle. It was dis­covered more than 50 years ago in the soil bac­terium Paracoccus. At that time, the meta­bolic path­way re­ceived little at­ten­tion and its ex­act bio­chem­ical pro­cesses re­mained un­ex­plored. Dr. Len­nart Schada von Borzyskowski, first au­thor of the cur­rent Nature pub­lic­a­tion, is a postdoc­toral fel­low in To­bias Er­b's de­part­ment at the Max Planck In­sti­tute for Ter­restrial Mi­cro­bi­o­logy in Mar­burg, dis­covered this meta­bolic path­way in the course of lit­er­at­ure re­search. "Look­ing at this meta­bolic path­way, I no­ticed that it should be more ef­fi­cient than the pro­cess pre­vi­ously as­sumed for the de­grad­a­tion of glycolic acid, and I wondered whether it might be more im­port­ant than ori­gin­ally as­sumed," the sci­ent­ist re­ports.

Globally distributed, ecologically significant

A co­oper­a­tion with sci­ent­ists from the Uni­versity of Mar­burg made it pos­sible to study the glycolic acid meta­bol­ism and its reg­u­la­tion in liv­ing mi­croor­gan­isms. "Now our task was to look for the pres­ence and activ­ity of these genes in mar­ine hab­it­ats and their eco­lo­gical sig­ni­fic­ance," To­bias Erb ex­plains. The co­oper­a­tion between the Mar­burg bio­chem­ists and the mar­ine re­search­ers at the Max Planck In­sti­tute in Bre­men proved to be highly fruit­ful, as the lat­ter have been study­ing the mar­ine com­munit­ies near Hel­go­land for years, in par­tic­u­lar the bac­terial pop­u­la­tions dur­ing and after algal blooms. In sev­eral ex­cur­sions on the high seas, the sci­ent­ists from Mar­burg and Bre­men meas­ured form­a­tion and con­sump­tion of glycolic acid dur­ing algal bloom in spring 2018. In­deed: the meta­bolic cycle was act­ively in­volved in the meta­bol­ism of glycolic acid.

The blue­prints of the meta­bolic cycle also were found re­peatedly in the bac­terial gen­ome se­quences that the TARA Oceans expedition had col­lec­ted from the world's oceans over a dis­tance of 10,000 kilo­met­ers, with a on av­er­age 20 times higher pre­val­ence than all other pos­tu­lated de­grad­a­tion routes for glycolic acid.