Hy­dro­thermal ca­ter­ing

Hy­dro­thermal vents in the deep sea are well-known oases of life. Many liv­ing creatures thrive there, be­ne­fit­ing from the nu­tri­ent-rich flu­ids that are com­monly the only source of en­ergy. The oc­cur­rence of hy­dro­thermal sys­tems is not lim­ited to the deep sea, however, but they are also found in nearshore shal­low wa­ters where sub­mar­ine vol­canic activ­ity is present. As in the deep sea, hot wa­ter rises up through the sed­i­ments and into the wa­ter column here, en­rich­ing the wa­ter in ma­ter­i­als dis­solved from the Earth’s in­terior. As an ex­ample, near-coastal hy­dro­thermal sys­tems are present off the Greek is­land of Mi­los, which is the study area of the in­vest­ig­at­ing au­thors. Here the sci­ent­ists have no need of ex­pens­ive tech­no­logy like sub­mers­ible vehicles for tak­ing samples or the in­stall­a­tion of ob­ser­vat­or­ies. The study area is within snorkel­ing dis­tance of the coast.

Here, mi­crobes use the pro­cess of chemo­syn­thesis to ob­tain en­ergy from in­or­ganic chem­ical com­pounds and to trans­form car­bon di­ox­ide into bio­mass. At hy­dro­thermal vents in the deep sea this is the basis of the sym­bi­osis between bac­teria and an­im­als.

In or­der to study the mi­croor­gan­isms and their mech­an­isms of chem­ical meta­bol­ism, Sol­veig Bühring of MARUM and Stefan Siev­ert of the Woods Hole Ocean­o­graphic In­sti­tu­tion (WHOI) tried, with the help of their team, to re­cre­ate the liv­ing con­di­tions of the mi­croor­gan­isms in the labor­at­ory – with mod­er­ate suc­cess. Be­cause of the low rates of meta­bol­ism they ob­served here, the team de­cided to in­stall in­cub­at­ors dir­ectly on the sea floor in or­der to study the mi­cro­bial com­munity within the nat­ural sys­tem of hy­dro­thermal fluid cir­cu­la­tion. The in­cub­at­ors used by the sci­ent­ists are the same as those that are ac­tu­ally in­stalled by sub­mers­ible vehicles in hun­dreds of meters of wa­ter. With this method, Siev­ert, Bühring and their co-au­thors es­tab­lished a new pro­ced­ure for study­ing the mi­cro­bi­o­logy of shal­low-wa­ter sys­tems.

“In­stead of diving ro­bots, we were able to carry out our ex­per­i­ments dir­ectly in the sed­i­ment. First, we in­stalled the in­cub­at­ors, a kind of pipe that is open on both ends. These be­came the points of ex­change between the oxy­gen-rich sea­wa­ter and the sulf­ide-con­tain­ing hy­dro­thermal flu­ids that are flow­ing up­ward,” ex­plains Stefan Siev­ert.

Us­ing the in­cub­at­ors, labeled car­bon di­ox­ide in­jec­ted into the sed­i­ment and its up­take in mi­cro­bial fatty acids, in con­junc­tion with DNA and RNA meth­ods, re­veal which mem­bers of the mi­cro­bial com­munity are the primary fix­ers of car­bon. The ways in which the mi­cro­bial com­munit­ies change un­der new con­di­tions was also stud­ied, for ex­ample, when the cir­cu­la­tion of hy­dro­thermal flu­ids is cut off.

“We no­ticed that the com­munity is ex­tremely dy­namic. As soon as the cir­cu­la­tion of hy­dro­thermal flu­ids was in­ter­rup­ted, the rates of car­bon fix­a­tion de­clined and the mi­cro­bial com­pos­i­tion altered to a com­munity re­sem­bling that of a reg­u­lar, non-hy­dro­therm­ally in­flu­enced coastal sed­i­ment­ary en­vir­on­ment. We were very sur­prised that this ad­apt­a­tion oc­curred within hours,” says Bühring.

Sol­veig Bühring sum­mar­izes: “Our work is rel­ev­ant be­cause shal­low-wa­ter sys­tems im­pact the coasts and there­fore, as in Mi­los, also in­flu­ence the en­vir­on­ments in which people live.” The flu­ids con­tain ma­ter­i­als that are po­ten­tially haz­ard­ous for hu­mans, such as hy­dro­gen sulf­ide, which is trans­formed into harm­less sul­fur and sulfate by the chemo­syn­thetic activ­ity of the mi­croor­gan­isms. The res­ults ob­tained by Siev­ert and Bühring also rep­res­ent a build­ing block in our un­der­stand­ing of the chemo­syn­thetic func­tions in mar­ine sys­tems, their im­pacts on the en­vir­on­ment, and the global car­bon cycle.

In gen­eral, Bühring and her col­leagues are in­ter­ested in gain­ing a bet­ter un­der­stand­ing of mi­croor­gan­isms. The im­port­ance of this is il­lus­trated by a re­cent ex­ample in which know­ledge from mi­cro­bi­o­logy has been ap­plied. The pro­ced­ure used in PCR test­ing in the Corona pan­demic is based on heat-stable en­zymes de­rived from mi­croor­gan­isms isol­ated from shal­low-wa­ter hy­dro­thermal sys­tems.

In the com­ing year, Bühring and her col­leagues will con­tinue to work on the hy­dro­thermal sys­tems off Mi­los. An ex­ped­i­tion with the Re­search Ves­sel MET­EOR is planned for the sum­mer of 2023. Its ob­ject­ive is to identify vents at a vari­ety of dif­fer­ent wa­ter depths and to fill the gaps in un­der­stand­ing between hy­dro­thermal sys­tems near the coasts and those in the deep sea.

Original publiCation

Stefan M. Sievert*, Solveig I. Bühring*, Lara K. Gulmann, Kai-Uwe Hinrichs, Petra Pop Ristova, Gonzalo V. Gomez-Saez: Fluid flow stimulates chemoautotrophy in hydrothermally influenced coastal sediments. Communications Earth & Environment 2022. DOI: 10.1038/s43247-022-00426-5 *shared first authorship

Further Information

• MARUM
• Official Press Release

Research Associates

MARUM – Cen­ter for Mar­ine En­vir­on­mental Sci­ences at the Uni­versity
Pet­ro­logy of the Ocean Crust
Dr. Solveig I. Bühring | sbuehring@marum.de

ContaCt

MARUM – Cen­ter for Mar­ine En­vir­on­mental Sci­ences at the Uni­versity
Public and Media Relations
Medien@marum.de

Header-Image: White bac­terial mats on the sea­floor show where flu­ids seep up through the sed­i­ment. Foto: Uni­ver­si­tät Bre­men / Tho­mas Pi­ch­ler