Abundance and diveristy of Alphaproteobacteria in the Southern Ocean: the dark side of SAR11
(English)Manuscript (preprint) (Other academic)
Alphaproteobacteria represented by lineages such as SAR11 and Roseobacter are ubiquitous and often dominant in marine bacterioplankton communities. The Southern Ocean is no exception even if annual extremes in light regime and autochthonous inputs of organic substrates present an environment that are in many ways very different from other oceanic regions. Using population mapping and community analysis of bacterioplankton during the highly dynamic summer season within the Ross and Amundsen Seas, in combination with experimental incubations under contrasting light regimes, we studied the impact of solar radiation and other environmental factors on individual lineages and populations within class Alphaproteobacteria. Quantitative population tracking by fluorescence in-situ hybridization was combined with pyrosequencing-derived 16S rRNA gene inventories to resolve the community beyond class and abundant lineages. Both experiments and depth-resolved distribution patterns confirm SAR11 as a major component of the bacterial community regardless of water mass and depth. However, the experiments revealed that SAR11 as a lineage was less competitive under solar-exposed conditions whereas the opposite response was observed for Roseobacter. Resolving the SAR11 linage into subclades, clear partitioning of groups between the different water masses and light regimes was observed. Also the diversity within the SAR11 lineage varied with significantly higher richness in the deeper, permanently dark water masses. Using this abundant marine bacterial lineage as a model, we could demonstrate clear separation of closely related bacterial populations between water masses and along environmental gradients of light exposure, oxygen availability, phytoplankton and nutrients. It is evident that such ecologically coherent populations can only be tracked at high phylogenetic resolution and that ecological and evolutionary mechanisms underpinning the observed phylogeographic patterns differ between water masses in the Southern Ocean.
Southern Ocean, Alphaproteobacteria, SAR11, Roseobacter, community composition, solar radiation
Research subject Biology with specialization in Evolutionary Genetics
IdentifiersURN: urn:nbn:se:uu:diva-245066OAI: oai:DiVA.org:uu-245066DiVA: diva2:790348