Seasonal dynamics of prokaryotes and their associations with diatoms in the Southern Ocean as revealed by an autonomous sampler

Abstract

The Southern Ocean remains one of the least explored marine environments. The investigation of temporal microbial dynamics has thus far been hampered by the limited access to this remote ocean. We present here high-resolution seasonal observations of the prokaryotic community composition during phytoplankton blooms induced by natural iron fertilization. A total of 18 seawater samples were collected by a moored remote autonomous sampler over 4 months at 5-11 day intervals in offshore surface waters (central Kerguelen Plateau). Illumina sequencing of the 16S rRNA gene revealed that among the most abundant amplicon sequence variants, SAR92 and Aurantivirga were the first bloom responders, Pseudomonadaceae, Nitrincolaceae and Polaribacter had successive peaks during the spring bloom decline, and Amylibacter increased in relative abundance later in the season. SAR11 and SUP05 were abundant prior to and after the blooms. Using network analysis, we identified two groups of diatoms representative of the spring and summer bloom that had opposite correlation patterns with prokaryotic taxa. Our study provides the first seasonal picture of microbial community dynamics in the open Southern Ocean and thereby offers biological insights to the cycling of carbon and iron, and to an important puzzling issue that is the modest nitrate decrease associated to iron fertilization.

Bacterioplankton Diversity and Distribution in Relation to Phytoplankton Community Structure in the Ross Sea surface waters

“…Previous studies have reported that Polaribacter species thrive during diatom-bloom (Teeling et al, 2012;Williams et al, 2012), potentially suggesting that their presence in the TNB area might be linked with the higher presence of diatom species we have identified. Similarly, a recent analysis revealed that species of the Aurantivirga genus are among the firsts prokaryotic taxa responding to diatom bloom in the Southern Ocean (Liu et al, 2020). Sequences related to the genus Aurantivirga are highly abundant in our TNB stations, suggesting once again a possible relationship with the high abundance of diatoms (Figure 9B).…”

The Polar Night Shift: Annual Dynamics and Drivers of Microbial Community Structure in the Arctic Ocean

“…5) matched microscopic cell counts in the Fram Strait 55 , corroborating our ampliconbased results. Similar autumn patterns in the Southern Ocean indicate bi-polar seasonal preferences of Coscinodiscophyceae diatoms, likely facilitated by their ability to overcome silicate limitation 56 , use ammonium instead of nitrate 22 , and resist grazing 57 . Appearance of chytrid fungi and fungi-like Labyrinthulaceae at maximal nutrient depletion in October (Extended Data Fig.…”

“…Coscinodiscophyceae in autumn, Aurantivirga and SAR92 as first bacterial responders, and Amylibacter at the summer-autumn transition 22 . This suggests fundamental "bi-polar" patterns of microbial seasonality, only discernable by autonomous sampling.…”

“…Due to the extreme winter conditions, year-round sampling in polar waters requires autonomous observations, recently providing the first comprehensive annual records in the Arctic and Antarctic 22,23 . Such approaches can identify transition phases in the interplay between ocean physics and the ecosystem, for instance the onset of the spring bloom or the end of net-growth.…”

North Sea spring bloom-associated Gammaproteobacteria fill diverse heterotrophic niches

“…These species are fewer in number, most likely reflecting the lower complexity of the low molecular weight fractions. They nonetheless are significant, given, for example, the reports for example of high abundances of the Nitrincolaceae (and in particular the genus ASP10-02a) from locations in both Northern and Southern Hemispheres [ 8 , 33 , 34 , 83 ].…”