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Stu­dio apart­ment: small-space niche form­a­tion at hy­dro­thermal vents

May 10, 2017

From burning hot to ice cold, from energy-rich to an exhausted desert - environmental conditions at deep-sea hot vents change dramatically at very small scales. Nevertheless, resident bacteria know exactly what they like best. Each one has their own ecological niche.

 

Liv­ing or­gan­isms in­hab­it­ing deep-sea hy­dro­thermal vents face quite some chal­lenges.

At such vents, wa­ter heated in the Earth’s in­terior exits the sea­floor at tem­per­at­ures of more than 300 de­grees Celsius. These high tem­per­at­ures be­come pos­sible due to enorm­ous pres­sure in the deep sea, which in­creases the boil­ing point of the wa­ter. Moreover, not the smal­lest sparkle of sun­light reaches these depths. Thus, the con­ver­sion of car­bon di­ox­ide into bio­mass through pho­to­syn­thesis, as done by plants, is im­possible. Other sources of en­ergy are re­quired. Mi­croor­gan­isms in the deep sea there­fore use chem­ical com­pounds such as meth­ane or sulf­ide, which stream from the hot vents, to grow. This way, they form the basis of the local food chain.

In this ex­treme hab­itat, the liv­ing con­di­tions for the local fauna change drastic­ally at very small scales. After emer­gence, the hot vent wa­ter mixes with the sur­round­ing, four de­grees cold sea­wa­ter and rap­idly cools. The same ap­plies to the con­tent of, for ex­ample, sulf­ide: Just a few cen­ti­metres from the vent open­ing, con­cen­tra­tions di­min­ish to only a frac­tion of their ori­ginal mag­nitude.

How do the res­id­ent mi­croor­gan­isms man­age to ad­apt to such a small-scale en­vir­on­ment?

Probenahme mit Quest
By dint of ROV Quest, Meier and his colleagues sampled fluids and water as well as different surfaces at hydrothermal vents in the Manus Basin (Source: MARUM – Center for Marine Environmental Sciences, University of Bremen)
Probenahme Dimitri Meier mit Quest
Probenahme Dimitri Meier mit Quest
Sampling sites (Source: MARUM – Center for Marine Environmental Sciences, University of Bremen)
Meier Bild Grafik
The bacteria inhabit tiny ecological niches – epsilonproteobacteria in the immediate vicinity of the vents, SUP05-bacteria further off. (Source: The ISME Journal)

Are there eco­lo­gical niches, as we know them from other hab­it­ats? The bio­lo­gist Di­mitri Meier and col­leagues from the Max Planck In­sti­tute for Mar­ine Mi­cro­bi­o­logy in Bre­men, to­gether with mar­ine re­search­ers from MARUM in Bre­men and Har­vard Uni­versity in Cam­bridge, USA, are in­vest­ig­at­ing these ques­tions in a new pub­lic­a­tion in The ISME Journal.

Who lives where is clearly regulated

On a re­search cruise to hy­dro­thermal vents in the Manus Basin off Papua New Guinea, the re­search­ers col­lec­ted gas and wa­ter samples as well as samples of dif­fer­ent sur­faces in the im­me­di­ate vi­cin­ity of the vents. In the labor­at­ory in Bre­men, they then ex­amined the mi­croor­gan­isms liv­ing there. The ex­am­in­a­tion showed that “who lives where” at the hot vents is clearly defined.

"Hy­dro­thermal vents around the world are mainly pop­u­lated by two groups of bac­teria", ex­plains Meier. "The so-called SUP05 gammapro­teo­bac­teria and ep­si­lon­pro­teo­bac­teria of the gen­era Sulfurovum and Sulfurimonas. We found clear evid­ence that the wide­spread SUP05 bac­teria are ad­ap­ted to low sulf­ide con­cen­tra­tions. The ep­si­lon­pro­teo­bac­teria, on the other hand, live much closer to the vent open­ing at much higher sulf­ide val­ues."

The ep­si­lon­pro­teo­bac­teria have some spe­cial skills to live in this in­fernal high-en­ergy hab­itat. "Our ana­lyses of their genes re­vealed that they pos­sess en­hanced sur­face at­tach­ment and stress res­ist­ance mech­an­isms", says Meier. "The SUP05 bac­teria lack these cap­ab­il­it­ies and thus can­not hold them­selves in tur­bu­lent and toxic mix­ing areas."

New insights into species formation in microorganisms

The study also sheds a new light on spe­cies form­a­tion in mi­croor­gan­isms. The re­search­ers found evid­ence that a bac­terial group can di­ver­sify into many dif­fer­ent gen­era and spe­cies if it is ex­posed to en­vir­on­mental con­di­tions vary­ing strongly at very small scales. The SUP05 bac­teria oc­cur­ring in con­stantly cold and mea­gre con­di­tions were rep­res­en­ted by few, very closely re­lated spe­cies. Within the ep­si­lon­pro­teo­bac­teria, on the other hand, there was a very high di­versity of spe­cies. This di­versity, however, does not mean that the dif­fer­ent spe­cies also take on dif­fer­ent func­tions in their hab­itat. The ge­netic make-up of the vari­ous spe­cies was com­par­able.

Yet, one thing stood out, the re­search­ers re­port: Cer­tain key genes en­cod­ing the sul­fur ox­id­a­tion were as di­verse as the marker genes used for spe­cies iden­ti­fic­a­tion. "Ap­par­ently, there are a lot of dif­fer­ent types of ep­si­lon­pro­teo­bac­teria that all ox­id­ise sulf­ide and bind car­bon di­ox­ide, but have spe­cial­ised on very spe­cific con­di­tions, such as dif­fer­ent sulf­ide con­cen­tra­tions," says Meier. "That is what we want to in­vest­ig­ate next."

 

Original publication

Di­mitri V. Meier, Petra Pje­vac, Wolfgang Bach, Stephane Hourdez, Peter R Gir­guis, Charles Vidoudez, Rudolf Amann and Anke Meyerdierks (2017): Niche par­ti­tion­ing of di­verse sul­fur-ox­id­iz­ing bac­teria at hy­dro­thermal vents. ISME Journal.

doi:10.1038/ismej.2017.37

 

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Dr. Fanni Aspetsberger
 
 
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