Abstract
We assessed the significance of cyanate utilization in marine primary productivity from the distribution of a dedicated transporter (encoded by cynABD ) in different ocean environments. Several lines of evidence indicate that the cyanate utilization potential is associated mainly with surface populations of Prochlorococcus . Spatial and temporal dimensions of cynA , cynS , and ntcA expression by picocyanobacteria in the northern Red Sea supported our previous finding that cynA transcripts accumulate under more stringent N‐limiting conditions. At the same time, cyanate utilization appeared to be more complex than suggested in our earlier publication, as we showed that picocyanobacteria also express their cyanate utilization potential under conditions where labile organic N compounds, such as urea, accumulate. These include N‐sufficient transient conditions that result from nutrient upwelling during early mixing events in autumn as well as during spring bloom conditions that follow deep mixing events. Our finding that cynA occurrence is common in diverse marine environments suggests that cyanate utilization may be of a more fundamental importance to picophytoplankton productivity than previously considered.