Distribution of Roseobacter RCA and SAR11 lineagesand distinct bacterial communities from the subtropicsto the Southern Ocean

摘要

We assessed the composition of the bacterioplanktonin the Atlantic sector of the Southern Ocean in australfall and winter and in New Zealand coastal watersin summer. The various water masses between thesubtropics/Agulhas–Benguela boundary region andthe Antarctic coastal current exhibited distinct bacte-rioplankton communities with the highest richness inthe polar frontal region, as shown by denaturinggradient gel electrophoresis of 16S rRNA gene frag-ments. The SAR11 Glade and the Roseobacter clade-affiliated (RCA) cluster were quantified by real-timequantitative PCR. SAR11 was detected in all samplesanalysed from subtropical waters to the coastalcurrent and to depths of > 1000 m. In fall and winter,this Glade constituted < 3% to 48% and 4-28% of totalbacterial 16S rRNA genes respectively, with highestfractions in subtropical to polar frontal regions. TheRCA cluster was only present in New Zealand coastalsurface waters not exceeding 17°C, in the Agulhas-Benguela boundary region (visited only during thewinter cruise), in subantarctic waters and in theSouthern Ocean. In fall, this cluster constituted up to36% of total bacterial 16S rRNA genes with highestfractions in the Antarctic coastal current and outnum-bered the SAR11 Glade at most stations in the polarfrontal region and further south. In winter, the RCAcluster constituted lower proportions than the SAR11Glade and did not exceed 8% of total bacterial 16SrRNA genes. In fall, the RCA cluster exhibited signifi-cant positive correlations with latitude and ammo-nium concentrations and negative correlations withconcentrations of nitrate, phosphate, and for near-surface samples also with chlorophyll a, biomass