Abstract
Many of the cyanobacterial species found in marine and saline environments have a gene encoding a putative nitrite transporter of the formate/nitrite transporter (FNT) family. The presumed function of the gene (designated nitM) was confirmed by functional expression of the gene from the coastal marine species Synechococcus sp. strain PCC7002 in the nitrite-transport-less mutant (NA4) of the freshwater cyanobacterium Synechococcus elongatus strain PCC7942. The NitM-mediated nitrite uptake showed an apparent Km (NO2−) of about 8 μM and was not inhibited by nitrate, cyanate or formate. Of the nitM orthologs from the three oceanic cyanobacterial species, which are classified as α-cyanobacteria on the basis of the occurrence of Type 1a RuBisCO, the one from Synechococcus sp. strain CC9605 conferred nitrite uptake activity on NA4, but those from Synechococcus sp. strain CC9311 and Prochlorococcus marinus strain MIT9313 did not. A strongly conserved hydrophilic amino acid sequence was found at the C-termini of the deduced NitM sequences from α-cyanobacteria, with a notable exception of the Synechococcus sp. strain CC9605 NitM protein, which entirely lacked the C-terminal amino acids. The C-terminal sequence was not conserved in the NitM proteins from β-cyanobacteria carrying the Type 1b RuBisCO, including the one from Synechococcus sp. strain PCC7002. Expression of the truncated nitM genes from Synechococcus sp. strain CC9311 and Prochlorococcus marinus strain MIT9313, encoding the proteins lacking the conserved C-terminal region, conferred nitrite uptake activity on the NA4 mutant, indicating that the C-terminal region of α-cyanobacterial NitM proteins inhibits the activity of the transporter.
Highlights
Contribution of marine primary producers to global net primary productivity is comparable to that of terrestrial primary producers [1]
Among the α-cyanobacterial strains, seven strains have the capacity of nitrate assimilation and eleven have the capacity of nitrite assimilation, with nine of the eleven strains carrying the gene for the putative nitrite transporter of the formate/nitrite transporter (FNT) family
The gene is closely linked to the nitrite reductase gene nirA in α-cyanobacteria, suggesting that the gene is associated with the capacity for nitrite assimilation
Summary
Contribution of marine primary producers to global net primary productivity is comparable to that of terrestrial primary producers [1]. The supply of nitrogen to marine phytoplankton in nutrient-rich region is largely through the uptake of nitrate and ammonium, dissolved organic nitrogen and dissolved dinitrogen gas significantly contribute to nutrition of marine plankton [2,3,4,5]. Concentrations of nitrate and ammonium are limited in most regions of the tropical and subtropical oceans and nitrogen availability has an important role in net primary productivity in these regions [6,7]. Picoplanktonic cyanobacteria of Synechococcus and Prochlorococcus strains are often the numerically dominant phytoplankton group and an important contributor to the net primary production in the tropical and subtropical oceans [8].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
