Functional Characterization of the FNT Family Nitrite Transporter of Marine Picocyanobacteria

Life

Shin-ichi Maeda¹  Akio Murakami³  Hisashi Ito³  Ayumi Tanaka³  Tatsuo Omata¹  John C. Meeks² 

[1] Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan; E-Mail:;Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan; E-Mail;CREST, Japan Science and Technology Agency, Chiyoda-ku, Tokyo 102-0076 Japan; E-Mails:

关键词: marine cyanobacteria;    nitrite;    transporter;   

DOI  :  10.3390/life5010432

来源: mdpi

【 摘 要 】

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 K_m (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.

【 授权许可】

CC BY   
© 2015 by the authors; licensee MDPI, Basel, Switzerland.