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Significant N? fixation by heterotrophs, photoheterotrophs and heterocystous cyanobacteria in two temperate estuaries.

ABSTRACT: Nitrogen (N) fixation is fueling planktonic production in a multitude of aquatic environments. In meso- and poly-haline estuaries, however, the contribution of N by pelagic N? fixation is believed to be insignificant due to the high input of N from land and the presumed absence of active N?-fixing organisms. Here we report N? fixation rates, nifH gene composition and nifH gene transcript abundance for key diazotrophic groups over 1 year in two contrasting, temperate, estuarine systems: Roskilde Fjord (RF) and the Great Belt (GB) strait. Annual pelagic N? fixation rates averaged 17 and 61?mmol N?m(-2) per year at the two sites, respectively. In RF, N? fixation was mainly accompanied by transcripts related to heterotrophic (for example, Pseudomonas sp.) and photoheterotrophic bacteria (for example, unicellular diazotrophic cyanobacteria group A). In the GB, the first of two N? fixation peaks coincided with a similar nifH-expressing community as in RF, whereas the second peak was synchronous with increased nifH expression by an array of diazotrophs, including heterotrophic organisms as well as the heterocystous cyanobacterium Anabaena. Thus, we show for the first time that significant planktonic N? fixation takes place in mesohaline, temperate estuaries and that the importance of heterotrophic, photoheterotrophic and photosynthetic diazotrophs is clearly variable in space and time.

SUBMITTER: Bentzon-Tilia M

PROVIDER: S-EPMC4303622 | biostudies-literature | 2015 Feb

REPOSITORIES: biostudies-literature

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Significant N₂ fixation by heterotrophs, photoheterotrophs and heterocystous cyanobacteria in two temperate estuaries.

Bentzon-Tilia Mikkel M Traving Sachia J SJ Mantikci Mustafa M Knudsen-Leerbeck Helle H Hansen Jørgen L S JL Markager Stiig S Riemann Lasse L

The ISME journal 20140715 2

Nitrogen (N) fixation is fueling planktonic production in a multitude of aquatic environments. In meso- and poly-haline estuaries, however, the contribution of N by pelagic N₂ fixation is believed to be insignificant due to the high input of N from land and the presumed absence of active N₂-fixing organisms. Here we report N₂ fixation rates, nifH gene composition and nifH gene transcript abundance for key diazotrophic groups over 1 year in two contrasting, temperate, estuarine systems: Roskilde ...[more]

PMID: 25026373

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Project description:Small RNAs (sRNAs) are a growing class of non-protein-coding transcripts that participate in the regulation of virtually every aspect of bacterial physiology. Heterocystous cyanobacteria are a group of photosynthetic organisms that exhibit multicellular behavior and developmental alternatives involving specific transcriptomes exclusive of a given physiological condition or even a cell type. In the context of our ongoing effort to understand developmental decisions in these organisms we have undertaken an approach to the global identification of sRNAs. Using differential RNA-Seq we have previously identified transcriptional start sites for the model heterocystous cyanobacterium Nostoc sp. PCC 7120. Here we combine this dataset with a prediction of Rho-independent transcriptional terminators and an analysis of phylogenetic conservation of potential sRNAs among 89 available cyanobacterial genomes. In contrast to predictive genome-wide approaches, the use of an experimental dataset comprising all active transcriptional start sites (differential RNA-Seq) facilitates the identification of bona fide sRNAs. The output of our approach is a dataset of predicted potential sRNAs in Nostoc sp. PCC 7120, with different degrees of phylogenetic conservation across the 89 cyanobacterial genomes analyzed. Previously described sRNAs appear among the predicted sRNAs, demonstrating the performance of the algorithm. In addition, new predicted sRNAs are now identified that can be involved in regulation of different aspects of cyanobacterial physiology, including adaptation to nitrogen stress, the condition that triggers differentiation of heterocysts (specialized nitrogen-fixing cells). Transcription of several predicted sRNAs that appear exclusively in the genomes of heterocystous cyanobacteria is experimentally verified by Northern blot. Cell-specific transcription of one of these sRNAs, NsiR8 (nitrogen stress-induced RNA 8), in developing heterocysts is also demonstrated.

Dataset Information

Significant N? fixation by heterotrophs, photoheterotrophs and heterocystous cyanobacteria in two temperate estuaries.

Publications

Significant N₂ fixation by heterotrophs, photoheterotrophs and heterocystous cyanobacteria in two temperate estuaries.

Similar Datasets

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