Abstract
Newly designed primers targeting rbcL (CO2 fixation), psbA (photosystem II) and rnpB (reference) genes were used in qRT-PCR assays to assess the photosynthetic capability of natural communities of Prochlorococcus, the most abundant photosynthetic organism on Earth and a major contributor to primary production in oligotrophic oceans. After optimizing sample collection methodology, we analyzed a total of 62 stations from the Malaspina 2010 circumnavigation (including Atlantic, Pacific and Indian Oceans) at three different depths. Sequence and quantitative analyses of the corresponding amplicons showed the presence of high-light (HL) and low-light (LL) Prochlorococcus clades in essentially all 182 samples, with a largely uniform stratification of LL and HL sequences. Synechococcus cross-amplifications were detected by the taxon-specific melting temperatures of the amplicons. Laboratory exposure of Prochlorococcus MED4 (HL) and MIT9313 (LL) strains to organic pollutants (PAHs and organochlorine compounds) showed a decrease of rbcL transcript abundances, and of the rbcL to psbA ratios for both strains. We propose this technique as a convenient assay to evaluate effects of environmental stressors, including pollution, on the oceanic Prochlorococcus photosynthetic function.
Highlights
Oceanic phytoplankton are responsible for almost a half of the global net primary production (NPP) [1], whereas marine picocyanobacteria account for 32 to 80% of primary production in the oligotrophic oceans [2,3,4,5]
Prochlorococcus is the smallest and most abundant photosynthetic organism known on Earth, ubiquitously found throughout the euphotic zone in tropical and subtropical oligotrophic oceans from 40° S to 40° N [6], with population abundances of about 105 cells/mL [7,8,9,10,11,12,13]
We focus on the photosynthetic activity of Prochlorococcus given its relevance as a primary producer in the global oceans
Summary
Oceanic phytoplankton are responsible for almost a half of the global net primary production (NPP) [1], whereas marine picocyanobacteria account for 32 to 80% of primary production in the oligotrophic oceans [2,3,4,5]. Prochlorococcus contributes significantly to the NPP in this latitudinal band [8, 14, 15], playing a relevant role in the global carbon cycle. There are two clades of Prochlorococcus, adapted to either high-light (HL) and low-light (LL) conditions [16]. They differ in a number of genetic and ecophysiological characteristics, including their divinyl-.
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