High dark CO2 fixation rates by active chemolithoautotrophic microbes along the water column (100-5000m) off Galicia (NW Iberian margin)

High da k CO2 ixa ion a es by ac i e chemoli hoau o ophic mic obes along he wa e column (100 – 5000 m) o Galicia (NW Ibe ian ma gin) Ma a M Va ela1, Elisa Gue e o-Feijóo1, E a Sin es2 and Ge ha d J He ndl2, 3 1Ins i u o Español de Oceanog a ía (IEO), A Co uña, Spain. 2Uni e si y o Vienna, Depa men o Ma ine Biology, Facul y Cen e o Ecology, Aus ia. 3Royal Ne he lands Ins i u e o Sea Resea ch (NIOZ), Depa men o Biological Oceanog aphy, The Ne he lands. P e ious s udies ha e p o ided e idences ha mic obial chemoli hoau o ophic ac i i y u ns o be subs an ially la ge han hi he o assumed, which could ep esen a signi ican sou ce o au och honous ca bon supply in he da k ocean. By using iso opic labeling, we quan i ied DIC (dissol ed ino ganic ca bon) ixa ion a es (14C-bica bona e) and compa ed i wi h mic obial he e o ophic p oduc ion (3H-Leucine) in he subsu ace, meso- and ba hypelagic wa e s o he no hwes e n coas o he Ibe ian Peninsula. Ou esul s e ealed ha mic obial DIC ixa ion, anging om 0.05 o 67.07 µmol C m-3 d-1, was sligh ly highe han he e o ophic ac i i y pa icula ly in he meso-pelagic wa e s. Combining mic oau o adiog aphy and luo escence in si u hyb idiza ion (MICRO-CARD-FISH), we con i med ha bo h Thauma chaeo a and some bac e ial g oups, such as SAR 202, SAR 324, SAR 406 and Al e omonas ac i ely up ake DIC. Quan i a i e PCR (QPCR) da a e ealed ha Thauma chaeo a, inhabi ing he da k wa e s o he Galician ecosys em, con ain he gene o ammonia oxida ion and hus a e likely chemoau o ophics. QPCR esul s showed a highe abundance o he hauma chaeal 16S RNA and he low ammonia concen a ion (LAC)-amoA eco ype genes in meso- and lowe ba hypelagic wa e s han in su ace wa e s. In con as , high ammonia concen a ion (HAC)-amoA eco ype domina ed he subsu ace samples. Redundancy analysis (RDA) displayed ha en i onmen al and biological a iables, such as ni i e and oxygen concen a ion and he a io be ween LAC and HAC-amoA gene, co ela ed signi ican ly wi h he single-cell iden i ica ion o ac i e da k bica bona e ixe s and i s e ical dis ibu ion. Ou esul s p o ide e idence o he signi ican con ibu ion o chemoli ho ophy by speci ic a chaeal and bac e ial g oups in he da k ocean.