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Re­search Pro­jects

>The impact of anaerobic ammonium oxidation on the oceanic nitrogen cycle
>The role of large nitrate storing bacteria in the marine nitrogen cycling

Scientist

Biogeochemistry Group

Dr. Gaute Lavik

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

Room: 

3136

Phone: 

+49 421 2028-6510

Dr. Gaute Lavik

The impact of anaerobic ammonium oxidation on the oceanic nitrogen cycle

The avail­ab­il­ity of fixed in­or­ganic ni­tro­gen (ni­trate, ni­trite and am­monium) lim­its primary pro­ductiv­ity in many oceanic re­gions and con­trols at­mo­spheric car­bon di­ox­ide con­cen­tra­tions on geo­lo­gical time scales. The con­ver­sion of ni­trate to N2 by het­ero­trophic bac­teria (de­ni­tri­fic­a­tion) is be­lieved to be the only im­port­ant sink for fixed in­or­ganic ni­tro­gen in the ocean. Re­cently, we provided evid­ence for the abund­ance and activ­ity of auto­trophic bac­teria that an­aer­obic­ally ox­id­ize am­monium with ni­trite to N2 in the world's largest an­oxic basin, the Black Sea (Kuypers et al., in press). Phylo­gen­etic ana­lysis of 16S ri­bosomal RNA gene se­quences shows that the bac­teria are re­lated to deep-branch­ing mem­bers of the or­der Planc­to­my­cetales per­form­ing the Anam­mox (an­aer­obic am­monium ox­id­a­tion) pro­cess in am­monium-re­mov­ing biore­act­ors. Nu­tri­ent pro­files, fluor­es­cently la­belled RNA probes, 15N tracer ex­per­i­ments, and the dis­tri­bu­tion of spe­cific lad­der­ane mem­brane lip­ids in­dic­ate that am­monium dif­fus­ing up­wards from the an­oxic deep wa­ter is ef­fect­ively con­sumed by anam­mox bac­teria in the sub­oxic zone of the Black Sea. These res­ults demon­strate that anam­mox bac­teria are abund­ant and play an im­port­ant role in the ni­tro­gen cycle of the Black Sea. In fact, the wide­spread oc­cur­rence of am­monium con­sump­tion in sub­oxic mar­ine wa­ters as well as in sed­i­ments sug­gests that anam­mox bac­teria could play an im­port­ant but as yet neg­lected role in the oceanic loss of fixed ni­tro­gen. It is pro­posed to study this po­ten­tially im­port­ant pro­cess in the mar­ine ni­tro­gen cycle in a col­lab­or­at­ive pro­ject with the In­sti­tute of Baltic Sea Re­search-Warnemünde (IOW), University of Nijmegen and Royal Neth­er­lands In­sti­tute for Sea Re­search (NIOZ) in dif­fer­ent mar­ine set­tings by (1) de­term­in­ing high res­ol­u­tion nu­tri­ent and (2) lipid pro­files, (3) DNA/​RNA ana­lyses, (4) de­term­in­a­tion of anam­mox rates us­ing 15N and 13C la­belled sub­strates and (5) cul­tiv­a­tion. This com­bined ef­fort will provide a highly needed in­sight into the role of anam­mox bac­teria for the loss of fixed in­or­ganic ni­tro­gen in the ocean.

 

The role of large nitrate storing bacteria in the marine nitrogen cycling

Ni­trate is one of the main lim­it­ing nu­tri­ents in the ocean and its avail­ab­il­ity is of ma­jor im­port­ance to the mar­ine primary pro­duc­tion. Coastal wa­ters are of­ten char­ac­ter­ized by high nu­tri­ents (for dif­fer­ent reas­ons) lead­ing to high pro­ductiv­ity. The de­cay of or­ganic mat­ter con­sumes oxy­gen and res­ult in sub­oxic to an­oxic con­di­tions where there is a high flux of or­ganic mat­ter to the sed­i­ment and/​or low sup­ply of oxic bot­tom wa­ter. Un­der such con­di­tions ni­trate (NO3) is not only a nu­tri­ent source but also a source of oxy­gen (elec­tron ac­ceptor), and this is the do­main of the large ni­trate stor­ing sul­fur bac­teria; Beg­gia­toa, Thioploca and Thio­mar­gar­ita.
Our main fo­cus is on the im­plic­a­tions that the ap­pear­ance of these bac­teria have for the mar­ine ni­tro­gen cycle un­der dif­fer­ent con­di­tions. To what de­gree do they de­ni­trify (NO3 to N2 gas) which means a loss of ni­tro­gen from the mar­ine en­vir­on­ment? If they solely re­duce ni­trate to am­monium, do this in­crease eu­troph­ic­a­tion by keep­ing dis­solved ni­tro­gen in the wa­ter, or do they "leak out" ni­trate in an­oxic sed­i­ments and thus fuel the de­ni­tri­fi­ers and thus en­hance the loss of dis­solved ni­tro­gen?

Methods
We are both study­ing and mon­it­or­ing the an­nual changes in nat­ural en­vir­on­ments dur­ing ex­ped­i­tions to our field areas and grow­ing them in aquar­i­ums at our labor­at­ory. We are also aim­ing to de­velop pure cul­tures.
Both nat­ural and labeled ni­tro­gen iso­tope tech­niques to trace the faith of the ni­trate as well as nu­tri­ent meas­ure­ments (G. Lavik).
Mi­cro­scope stud­ies, like di­versity and bio­mass de­term­in­a­tion (A. Pre­isler), along with in­form­a­tion about the sed­i­ment­ary con­di­tions like pore wa­ter con­tent and grain-size dis­tri­bu­tion gives us in­form­a­tion about their pre­ferred and lim­it­ing con­di­tions.
Mi­cro elec­trode meas­ure­ments (E. Wi­eringa), among oth­ers, makes us able to mon­itor changes in the sed­i­ments (aquar­ium) un­der changed frame con­di­tions.
At the mo­ment our main study area is Eck­ern­förde near Kiel in the Baltic sea (Ger­many), but we have also ana­lysed sed­i­ments from the Wad­den Sea, Lim­f­jorden (Den­mark) and the Chilean and Nam­i­bian coast.
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