The cyanate utilization capacity of marine unicellular Cyanobacteria

Abstract

Cyanate, a by-product of urea decomposition, is a potential nitrogen (N) source in marine environments, but to date it has received scant attention. Cyanobacteria presumably acquire this compound via a substrate-specific ABC-type transporter (cynABD), and they convert it to ammonium and carbon dioxide by cyanase (cynS) activity. Participation of cyanate utilization genes in N-stress responses in cyanobacteria has been implied previously, but its ecological context has not been studied. We employed polymerase chain reaction protocols for cynA amplification to examine the potential for cyanate recruitment in the Gulf of Aqaba, northern Red Sea. We also monitored growth of cyanobacterial strains with different cynABDS complements on cyanate-containing media. We showed that cyanate is utilized as the sole N source by strains with the full gene complement, and residual growth, fed by natural decay of cyanate to ammonium, was observed in strains lacking any of these genes. Natural abundance of cynA products in the oligotrophic Gulf of Aqaba indicates that cyanate constitutes an essential N source for Prochlorococcus, but not for Synechococcus populations. Noncyanobacterial cynA sequences indicate cyanate utilization by a variety of other phototrophic microorganisms. We hypothesize that in stratified water bodies, cyanate utilization is confined to the N-deplete upper photic zone, where it plays a role in ''regenerated'' primary production.

Physiology and evolution of nitrate acquisition in Prochlorococcus

“…Genomic islands have also been identified (for example, the large region within LLI clade genomes such as NATL1A) by predicted gene gain events along the chromosome (Kettler et al, 2007). utilizing cyanate (Supplementary Figure S1) as the sole source of nitrogen. Although very little is known about cyanate concentrations in marine systems, cynA genes (encoding the periplasmic component of the cyanate ABC-type transporter system) were relatively abundant in the seasonally stratified and nitrogen depleted waters of the northern Red Sea (Kamennaya et al, 2008). The cynA gene of SB clusters with clones obtained from the Red Sea (Supplementary Figure S7), supporting their origin in HLII clade genomes as hypothesized by Kamennaya et al (2008).…”

“…Although very little is known about cyanate concentrations in marine systems, cynA genes (encoding the periplasmic component of the cyanate ABC-type transporter system) were relatively abundant in the seasonally stratified and nitrogen depleted waters of the northern Red Sea (Kamennaya et al, 2008). The cynA gene of SB clusters with clones obtained from the Red Sea (Supplementary Figure S7), supporting their origin in HLII clade genomes as hypothesized by Kamennaya et al (2008).…”

“…Furthermore, SB possesses cyanate transporter genes that are rare in both Prochlorococcus and Synechococcus strains (Kamennaya et al, 2008), and it can indeed grow Figure 4 Locations of nitrate and cyanate assimilation genes in strains of Prochlorococcus capable of nitrate assimilation relative to the known genomic islands (shaded regions) observed in the HLII and LLI clades of Prochlorococcus; plots modified from Kettler et al (2007). Prochlorococcus genomes are highly syntenic and genomic islands have been identified in HL adapted genomes (for example, AS9601) by conserved breaks in gene synteny among strains Kettler et al, 2007).…”

Ecological Genomics of Marine Picocyanobacteria

“…This region contains genes for nitrate, nitrite, urea, and cyanate assimilation, which, with the exception of the last, are the best known N sources in marine cyanobacteria. Among these, cyanate has only recently been identified as a potential N source in marine environments (129). Interestingly, the gene clusters for assimilation of different N sources are scattered across the genome of the deeply branching subcluster 5.2 strain Synechococcus sp.…”

“…Interestingly, Synechococcus sp. strains WH7803 and WH7805 carry a urtA-like gene that is phylogenetically distinct (129). This gene again does not form part of an operon, and its role, if any, in N acquisition and N stress responses remains elusive for now.…”