Sym­bi­oses from hy­dro­thermal vents and cold seeps

Rimicaris shrimp

K. van der Heijden, C. Borowski

The aim of this study is to shed light on the evol­u­tion­ary his­tory of Bathymodiolus mus­sels at the Mid-At­lantic Ridge. Previous phylogenetic analyses of the mussels showed that the clas­sical marker gene for phylo­gen­etic as­sess­ment, the mi­to­chon­drial mt­COI, does not provide enough res­ol­u­tion to cla­rify the re­la­tion­ship within this group.
To in­vest­ig­ate the geo­graphic struc­ture, gene gene­a­lo­gies, and the ma­jor dir­ec­tions and re­l­at­ive amounts of his­tor­ical gene flow between the four mus­sel pop­u­la­tions at the Mid-At­lantic Ridge, we are us­ing a multi-locus ap­proach for this pop­u­la­tion ge­netic study. The res­ults of our ana­lyses are used to re­con­struct the evol­u­tion­ary his­tory of the mus­sel pop­u­la­tions which also provides us with in­sight on the col­on­iz­a­tion his­tory of the Mid-At­lantic Ridge.

M. Ücker

In the Bathymodiolus sym­bi­osis, little is known about the in­flu­ence of the sym­bionts on the evol­u­tion of the host des­pite many stud­ies that have been per­formed on the sym­bionts‘ physiology. Our study aims to un­der­stand the pop­u­la­tion struc­ture and dy­nam­ics of Bathymodiolus mus­sels and the role of sym­bi­oses in an­imal hy­brid­isa­tion. We ana­lyse mus­sel samples from a vent field at the Mid-At­lantic Ridge where two mus­sel spe­cies, B. azoricus and B. puteoserpentis, have been de­scribed to form vi­able hy­brids. We use dia­gnostic mark­ers and meta­ge­n­omic tech­niques to as­sess the hy­brid status of each mus­sel in­di­vidual and to in­vest­ig­ate the phylo­geny of host mi­to­chon­dria and the sym­bionts. We hope to shed new light on the sym­bi­osis in hy­brid Bathymodiolus mus­sels and in­vest­ig­ate ques­tions of sym­biont spe­cificity and re­cog­ni­tion. Un­der­stand­ing hy­brid­isa­tion in sym­bi­otic an­im­als al­lows us to study spe­cies form­a­tion and evol­u­tion in nat­ural com­munit­ies and the role of bac­terial sym­bionts in these pro­cesses.

M. Franke, N. Leisch

Adult Bathymodiolus mus­sels har­bour their primary sym­bionts in the gill tis­sue. In ju­ven­ile mus­sels however, the sym­bionts col­on­ize not only the gills but also all other epi­thelial tis­sues within the mantle cav­ity. Only little is known about how and when sym­bionts first col­on­ize the mus­sels. To un­der­stand the pro­cesses and pref­er­ences of sym­biont col­on­iz­a­tion, we ex­am­ine early de­vel­op­mental stages of Bathymodiolus mus­sels. Us­ing a cor­rel­at­ive ima­ging ap­proach, which unites light- and elec­tron mi­cro­scopy with syn­chro­tron ra­di­ation-based X-ray mi­cro tomo­graphy, we are able to gen­er­ate a de­tailed three-di­men­sional mor­pho­lo­gical data­set. This data­set can be com­bined with sym­biont loc­al­iz­a­tion us­ing 16S rRNA FISH and al­lows us to de­term­ine the time of sym­biont col­on­iz­a­tion re­vealed by dis­tinct mor­pho­lo­gical ad­apt­a­tions dur­ing the de­vel­op­ment of the host. Our work serves as a start­ing point for fur­ther func­tional ana­lyses to elu­cid­ate how bac­teria can in­flu­ence and shape early eu­k­a­ryotic de­vel­op­ment.

B. Geier, M. Franke, E. So­gin, D. Michel­lod, M. Á. Gón­za­lez-Por­ras, A. Gruhl, N. Leisch, M. Liebeke

En­dosym­bi­oses such as in Bathymodiolus mus­sels are char­ac­ter­ized by in­tim­ate meta­bolic in­ter­ac­tions among the sym­bi­otic part­ners. Yet, we know very little about the nature of these in­ter­ac­tions in sym­bi­oses, par­tic­u­larly in their en­vir­on­mental con­text. There­fore, we cre­ated a spa­tial meta­bolo­m­ics pipeline (metaFISH) that links sym­biont gen­o­types with meta­bolic phen­o­types to al­low a spa­tial as­sign­ment of host and sym­biont meta­bol­ites at the scale of in­di­vidual host cells. We could ob­serve how the spa­tial chem­istry of host cells dif­fers with the pres­ence of in­tra­cel­lu­lar sym­bionts, found vari­ations in meta­bolic phen­o­types in a single sym­biont type and de­tec­ted novel meta­bol­ites. To gain a broader un­der­stand­ing of meta­bol­ite dis­tri­bu­tion at the scale of whole an­im­als, we also de­veloped a cor­rel­at­ive work­flow that al­lows ima­ging the 3D ana­tomy and mo­lecu­lar com­pos­i­tion of an­imal-mi­crobe sys­tems. The high spa­tial res­ol­u­tion gained be these ima­ging ap­proaches al­lows us to tackle some of the fun­da­mental ques­tion in sym­bi­osis re­search such as how do the sym­bi­otic part­ners in­ter­act.

M. Tietjen

To un­der­stand the cel­lu­lar in­ter­ac­tions between Bathymodiolus mus­sels and their in­tra­cel­lu­lar sym­bionts, we make use of ad­vanced next-gen­er­a­tion se­quen­cing tech­niques and in­vest­ig­ate gene ex­pres­sion pat­terns of both part­ners. In par­tic­u­lar, we are in­vest­ig­at­ing which gene (groups) are re­spons­ible for the main­ten­ance of the sym­bi­osis in the light of chan­ging en­vir­on­mental con­di­tions. One ex­ample for such con­di­tions is the lim­ited ac­cess to hy­dro­thermal flu­ids that carry es­sen­tial en­ergy sources for the sym­bionts such as sul­fur or meth­ane. Such vary­ing con­di­tions are ex­pec­ted to oc­cur reg­u­larly in hy­dro­thermal sys­tems. We sim­u­late such con­di­tions with in situ and labor­at­ory ex­per­i­ments, and com­pare the physiolo­gical re­sponses of both host and sym­bionts on the tran­scrip­tome and pro­teome level.

M. Á. Gónzalez-Porras, N. Leisch

Ca. En­do­nuc­leo­bac­ter is a gammapro­teo­bac­terial para­site that in­fects the nuc­lei of Bathymodiolus mus­sels. After a single Ca. En­do­nuc­leo­bac­ter cell in­vades the host nuc­leus, it pro­lif­er­ates massively (up to 80,000 bac­teria per nuc­leus) and the volume of the nuc­leus in­creases up to 50 fold. We in­vest­ig­ate how Ca. En­do­nuc­leo­bac­ter thrives in the nuc­leus, how it af­fects host cells and how it pre­vents the shut­down of the eu­k­a­ryotic cell (e.g. ap­op­tosis). To do so, we have se­quenced the gen­ome of the para­site and coupled laser cap­ture mi­cro­dissec­tion of in­fec­ted nuc­lei with ul­tra-low-in­put RNA-se­quen­cing. We are now in­vest­ig­at­ing how the tran­scrip­tional pro­files of para­site and host change along the in­fec­tious cycle. By tar­get­ing the tran­scrip­tomic pro­files of spe­cific life stages of an in­tra­nuc­lear para­site in situ, our pipeline closes the gap between the visual, mo­lecu­lar and tem­poral char­ac­ter­iz­a­tion of a para­site-host in­ter­ac­tion.

R. Ansorge, M. Á. Gón­za­lez-Por­ras

Bey­ond spe­cies bound­ar­ies, small ge­n­omic changes can strongly im­pact the life­style of a bac­terial strain. However, cur­rently it is not well un­der­stood how strain-level di­versity in sym­bi­oses emerges, per­sists and if or how it im­pacts mu­tu­al­istic as­so­ci­ations. We de­veloped a meta­ge­n­om­ics ap­proach to tease apart strain-level differences in Bathymodiolus symbionts and dis­covered strik­ing func­tional dif­fer­ences among co-oc­cur­ring sym­biont strains. This high res­ol­u­tion al­lows us to study sym­biont pop­u­la­tion struc­ture that helps us un­der­stand sym­biont col­on­iz­a­tion dy­nam­ics. Us­ing cul­tiv­a­tion-in­de­pend­ent meth­ods our re­search provides a snap­shot of the sym­bi­osis in its nat­ural con­text, al­low­ing us to in­vest­ig­ate how such strain di­versity evolved, per­sists and how it com­pares to free-liv­ing re­l­at­ives of the sym­bionts.

P. Bourceau

Over the last years, our omic ap­proaches have given us in­sights into the in­tric­ate re­la­tion­ship and meta­bolic in­ter­ac­tion between the Bathymodiolus hosts and their sym­bionts. To fully show that par­tic­u­lar pro­cesses take place, we ap­ply ma­nip­u­lat­ive ex­per­i­ments with sym­biont re­l­at­ives such as Methyloprofundus sedimenti, as cul­tur­ing Bathymodiolus sym­bionts re­mains chal­len­ging. By us­ing con­trolled in­cub­a­tion ex­per­i­ments and mass-spec­tro­metry based ana­lyses of the meta­bolome, we can meas­ure traits of the M. sedimenti gen­ome that are shared with the meth­ane-ox­id­ising sym­biont of Bathymodiolus mus­sels. Not only can we identify pos­sible sub­strates but also ex­creted meta­bol­ites, which could po­ten­tially be avail­able to the host. Our over­all aim is to char­ac­ter­ize meta­bolic mark­ers linked to en­vir­on­mental con­di­tions to con­clude the re­cent his­tory of a spe­ci­men from the deep-sea with meta­bolo­m­ics data.

Expedition Blog of Research Cruise SO253

One of the most abund­ant an­im­als at hy­dro­thermal vent sys­tems of the West­ern Pa­cific is the snail Ifremeria nautilei. These hosts har­bor at least 4 bac­terial sym­bionts in their gills, sulf­ide- and meth­ane-ox­id­iz­ing gammapro­teo­bac­teria and at least 2 al­phapro­teo­bac­terial phylo­types of un­known func­tion. We are cur­rently us­ing com­par­at­ive se­quence ana­lysis of phylo­gen­etic and func­tional genes to gain a bet­ter un­der­stand­ing of these sym­bi­oses (Borowski et al. in prep.).