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The mesopelagic anoxic Black Sea as an unexpected habitat for Synechococcus challenges our understanding of global "deep red fluorescence".

ABSTRACT: The Black Sea is the largest meromictic sea with a reservoir of anoxic water extending from 100 to 1000?m depth. These deeper layers are characterised by a poorly understood fluorescence signal called "deep red fluorescence", a chlorophyll a- (Chl a) like signal found in deep dark oceanic waters. In two cruises, we repeatedly found up to 10³ cells ml^-1 of picocyanobacteria at 750?m depth in these waters and isolated two phycoerythrin-rich Synechococcus sp. strains (BS55D and BS56D). Tests on BS56D revealed its high adaptability, involving the accumulation of Chl a in anoxic/dark conditions and its capacity to photosynthesise when re-exposed to light. Whole-genome sequencing of the two strains showed the presence of genes that confirms the putative ability of our strains to survive in harsh mesopelagic environments. This discovery provides new evidence to support early speculations associating the "deep red fluorescence" signal to viable picocyanobacteria populations in the deep oxygen-depleted oceans, suggesting a reconsideration of the ecological role of a viable stock of Synechococcus in dark deep waters.

SUBMITTER: Callieri C

PROVIDER: S-EPMC6776005 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature

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The mesopelagic anoxic Black Sea as an unexpected habitat for Synechococcus challenges our understanding of global "deep red fluorescence".

Callieri Cristiana C Slabakova Violeta V Dzhembekova Nina N Slabakova Nataliya N Peneva Elisaveta E Cabello-Yeves Pedro J PJ Di Cesare Andrea A Eckert Ester M EM Bertoni Roberto R Corno Gianluca G Salcher Michaela M MM Kamburska Lyudmila L Bertoni Filippo F Moncheva Snejana S

The ISME journal 20190228 7

The Black Sea is the largest meromictic sea with a reservoir of anoxic water extending from 100 to 1000 m depth. These deeper layers are characterised by a poorly understood fluorescence signal called "deep red fluorescence", a chlorophyll a- (Chl a) like signal found in deep dark oceanic waters. In two cruises, we repeatedly found up to 10<sup>3</sup> cells ml<sup>-1</sup> of picocyanobacteria at 750 m depth in these waters and isolated two phycoerythrin-rich Synechococcus sp. strains (BS55D an ...[more]

PMID: 30820035

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Project description:Spatial patterns of marine Synechococcus diversity across ocean domains have been reported on extensively. However, much less is known of seasonal and multiannual patterns of change in Synechococcus community composition. Here we report on the genotypic diversity of Synechococcus populations in the Gulf of Aqaba, Northern Red Sea, over seven annual cycles of deep mixing and stabile stratification, using ntcA as a phylogenetic marker. Synechococcus clone libraries were dominated by clade II and XII genotypes and a total of eight different clades were identified. Inclusion of ntcA sequences from the Global Ocean Sampling database in our analyses identified members of clade XII from beyond the Gulf of Aqaba, extending its known distribution. Most of the Synechococcus diversity was attributed to members of clade II during the spring bloom, while clade III contributed significantly to diversity during summer stratification. Clade XII diversity was most prevalent in fall and winter. Clade abundances were estimated from pyrosequencing of the V6 hypervariable region of 16S rRNA. Members of clade II dominated Synechococcus communities throughout the year, whereas the less frequent genotypes showed a pattern of seasonal succession. Based on the prevailing nutritional conditions we observed that clade I members thrive at higher nutrient concentrations during winter mixing. Clades V, VI and X became apparent during the transition periods between mixing and stratification. Clade III became prominent during sumeer stratification. We propose that members of clades V, VI, and X, and clade III are Synechococcus ecotypes that are adapted to intermediate and low nutrient levels respectively. This is the first time that molecular analyses have correlated population dynamics of Synechococcus genotypes with temporal fluctuations in nutrient regimes. Since these Synechococcus genotypes are routinely observed in the Gulf of Aqaba we suggest that seasonal fluctuations in nutrient levels create temporal niches that sustain their coexistence.

Dataset Information

The mesopelagic anoxic Black Sea as an unexpected habitat for Synechococcus challenges our understanding of global "deep red fluorescence".

Publications

The mesopelagic anoxic Black Sea as an unexpected habitat for Synechococcus challenges our understanding of global "deep red fluorescence".

Similar Datasets

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