H₂ accumulation and N₂ fixation variation by Ni limitation in Cyanothece

• Published in: Limnology and oceanography Vol. 65; no. 2; pp. 377 - 386
• Main Authors: Tuo, Sing-how, Rodriguez, Irene B., Ho, Tung-Yuan
• Format: Journal Article
• Language: English
• Published: Hoboken, USA John Wiley and Sons, Inc 01.02.2020; John Wiley & Sons, Inc
• ISSN: 0024-3590; 1939-5590
• DOI: 10.1002/lno.11305

Ni is an essential cofactor in NiFe-uptake hydrogenase, an enzyme regulating H₂ metabolism in diazotrophic cyanobacteria, the major H₂ producers in the surface ocean globally. Here, we investigated the effect of Ni supply on H₂ production and N₂ fixation by using a model marine cyanobacterial diazotroph, Cyanothece. By mediating total dissolved Ni concentrations from 100 to 0.03 nmol L−1 in a trace metal-defined culture medium, we demonstrated that Ni deficiency results in H₂ accumulation, coupled with decreasing Ni quotas, growth rates, and occasionally relatively low N₂ fixation rates. These results indicate that Ni deficiency limits the growth of the Cyanothece to some extent, considerably decreases H₂ uptake by hydrogenase and leads to H₂ accumulation and N₂ fixation variation in the diazotroph. The findings show that Ni availability is a critical factor on controlling H₂ production and N₂ fixation in marine diazotrophic cyanobacteria. The information of Ni bioavailability for diazotrophic cyanobacteria is thus essential to evaluate the importance of Ni for H₂ cycling and N₂ fixation in oceanic surface waters.