| Title | The genome of a freshwater planktonic Synechococcus strain reveals the potentiality to fix nitrogen |
| Abstract | The non-heterocystous diazotrophic (N-fixing) unicellular cyanobacteria of small size have been recognized to be important in marine system and can contribute to the oceanic nitrogen fixation substantially. Certain Synechococcus strains showed nitrogenase activity only under anaerobic conditions, others are active also under microaerobic conditions, like the Synechococcus SF1, capable of photosynthesis and N fixation. The Synechococcus marine strains Miami BG43511 and BG43522 developed a kind of temporal regulation: N2 fixation is performed during dark and photosynthesis during light. Nevertheless, there are no evidences of the existence of planktonic freshwater Synechococcus with the potentiality of N2 fixation. We selected one Synechococcus strain isolated from a volcanic lake in central Italy, previously sequenced for the 16S DNA gene, we sequenced the entire genome focussing on the nifHDK operon genes. The presence of these genes indicate the potentiality to perform the nitrogen fixation. From the GC% content difference between the nif operon and the other genes it is possible to hypothesize a HGT for the gene acquisition. To evaluate if the genes could be active we carried out a laboratory experiment growing the strain in media with and without nitrogen and following its growth and RNA expression. Synechococcus LL was able to grow in both conditions but without fixing nitrogen, as nifHDK were not expressed. As the cultures without N bleached, losting their pigments, we hypothesize that Synechococcus could have used internal nitrogen reserve, instead of activating nitrogen fixation genes. |
| Source | XXIII Congresso della Associazione Italiana di Oceanologia e Limnologia "Funzionamento, alterazioni e recupero degli ecosistemi acquatici. Le scienze acquatiche per comprendere i cambiamenti e per renderne i cittadini consapevoli", Cagliari, 26-29 settembre 2017 |
| Keywords | Synechococcus; Cyanobacteria; Nitrogen fixation; Nif gene |
| Year | 2017 |
| Type | Presentazione |
| Authors | Callieri C., Di Cesare A., Cabello Yeves P. J., Cristmas N., Salcher M., Sanchez-Baracaldo P. |
| Text | 385501 2017 Synechococcus; Cyanobacteria; Nitrogen fixation; Nif gene The genome of a freshwater planktonic Synechococcus strain reveals the potentiality to fix nitrogen Callieri C., Di Cesare A., Cabello Yeves P. J., Cristmas N., Salcher M., Sanchez Baracaldo P. CNR ISE, Evolutionary Genomics Group, Departamento de Produccion Vegetal y Microbiologia, Universidad Miguel Hernandez, San Juan de Alicante, Spain; School of Geographical Sciences, University of Bristol, Bristol BS8 1SS, UK; Limnological Station, Institute of Plant Biology, University of Zurich, Seestrasse 187, 8802 Kilchberg, Switzerland The non heterocystous diazotrophic N fixing unicellular cyanobacteria of small size have been recognized to be important in marine system and can contribute to the oceanic nitrogen fixation substantially. Certain Synechococcus strains showed nitrogenase activity only under anaerobic conditions, others are active also under microaerobic conditions, like the Synechococcus SF1, capable of photosynthesis and N fixation. The Synechococcus marine strains Miami BG43511 and BG43522 developed a kind of temporal regulation N2 fixation is performed during dark and photosynthesis during light. Nevertheless, there are no evidences of the existence of planktonic freshwater Synechococcus with the potentiality of N2 fixation. We selected one Synechococcus strain isolated from a volcanic lake in central Italy, previously sequenced for the 16S DNA gene, we sequenced the entire genome focussing on the nifHDK operon genes. The presence of these genes indicate the potentiality to perform the nitrogen fixation. From the GC% content difference between the nif operon and the other genes it is possible to hypothesize a HGT for the gene acquisition. To evaluate if the genes could be active we carried out a laboratory experiment growing the strain in media with and without nitrogen and following its growth and RNA expression. Synechococcus LL was able to grow in both conditions but without fixing nitrogen, as nifHDK were not expressed. As the cultures without N bleached, losting their pigments, we hypothesize that Synechococcus could have used internal nitrogen reserve, instead of activating nitrogen fixation genes. Published version XXIII Congresso della Associazione Italiana di Oceanologia e Limnologia Funzionamento, alterazioni e recupero degli ecosistemi acquatici. Le scienze acquatiche per comprendere i cambiamenti e per renderne i cittadini consapevoli Cagliari 26 29 settembre 2017 Nazionale Contributo PPT 2017_PPT_Callieri_AIOL.pdf Presentazione cristiana.callieri CALLIERI CRISTIANA andrea.dicesare DI CESARE ANDREA |
