JU­LIE LAROCHE: Dy­nam­ics of mi­cro­bial com­munity struc­ture and ...

Primary pro­ductiv­ity is lim­ited by the avail­ab­il­ity of fixed ni­tro­gen in large re­gions of theoceans. Dinitro­gen fix­a­tion, the only bio­lo­gical in­put path­way into the mar­ine N cycle, is anen­er­get­ic­ally ex­pens­ive bio­chem­ical pro­cess that re­duces N2 gas into NH3, a form of fix­ed­nitro­gen that is read­ily in­cor­por­ated into bio­molecules. The ni­tro­gen fix­ers, or diazo­trophs,are a se­lec­ted group of proka­ryotic mi­croor­gan­isms that can carry out this bio­chem­ic­al­pro­cess. His­tor­ic­ally, mar­ine ni­tro­gen fix­a­tion was thought to be a pro­cess car­ried outprimar­ily by cy­anobac­teria and im­port­ant mainlyin the trop­ical and sub­trop­ical oli­go­troph­icwa­ters. Re­cent real­iz­a­tion con­cern­ing the wide di­versity of mar­ine mi­crobes har­bor­ing thenitro­genase en­zyme in­dic­ates that we do not­fully un­der­stand ther­oles of the di­verse­diazo­trophs that pop­u­late the ocean.

In the con­text of the Ocean Fron­tier In­sti­tute loc­ated at­Dal­housie Uni­versity, the mi­cro­bial com­munity struc­ture and func­tion in North­w­est At­lantic(NWA) have been as­sessed through next-gen­er­a­tion se­quen­cing of hy­per­vari­able re­gions of16S and 18S rRNA genes, nifH gene and meta­ge­n­om­ics at ex­ist­ing time-series sta­tions since2014. The nifH gene, a marker gene for diazo­trophy, has shown that both cy­anobac­terial andnon-cy­anobac­terial diazo­trophs are mem­bers of the mi­cro­bial com­munit­ies in our NWA­mic­ro­bial ob­ser­vat­or­ies. The lec­ture will fo­cus on the mi­cro­bial com­munity struc­ture in th­eNWA, with a spe­cific at­ten­tion to the diazo­trophs. In par­tic­u­lar, the po­ten­tial meta­bol­icpath­ways iden­ti­fied from the gen­ome an­nota­tionof a novel bac­terial isol­ate, be­long­ing to aclade of gamma-pro­teo­bac­teria widely dis­trib­uted in the Tara ex­ped­i­tion data­base, will be­dis­cussed in a global con­text.