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Life 2015, 5(1), 432-446; doi:10.3390/life5010432

Functional Characterization of the FNT Family Nitrite Transporter of Marine Picocyanobacteria

1
Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan
2
CREST, Japan Science and Technology Agency, Chiyoda-ku, Tokyo 102-0076 Japan
3
Research Center for Inland Seas, Kobe University, Awaji, Hyogo 656-2401, Japan
4
Institute of Low Temperature Science, Hokkaido University, Kita-ku, Sapporo 060-0819, Japan
*
Author to whom correspondence should be addressed.
Academic Editors: John C. Meeks and Robert Haselkorn
Received: 1 December 2014 / Accepted: 29 January 2015 / Published: 9 February 2015
(This article belongs to the Special Issue Cyanobacteria: Ecology, Physiology and Genetics)
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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. View Full-Text
Keywords: marine cyanobacteria; nitrite; transporter marine cyanobacteria; nitrite; transporter
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Maeda, S.-I.; Murakami, A.; Ito, H.; Tanaka, A.; Omata, T. Functional Characterization of the FNT Family Nitrite Transporter of Marine Picocyanobacteria. Life 2015, 5, 432-446.

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