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.