Differential Transcriptional Analysis of the Cyanobacterium Cyanothece sp. Strain ATCC 51142 during Light-Dark and Continuous-Light Growth

Abstract

We analyzed the metabolic rhythms and differential gene expression in the unicellular, diazotrophic cyanobacterium Cyanothece sp. strain ATCC 51142 under N 2 -fixing conditions after a shift from normal 12-h light-12-h dark cycles to continuous light. We found that the mRNA levels of ϳ10% of the genes in the genome demonstrated circadian behavior during growth in free-running (continuous light) conditions. The genes for N 2 fixation displayed a strong circadian behavior, whereas photosynthesis and respiration genes were not as tightly regulated. One of our main objectives was to determine the strategies used by these cells to perform N 2 fixation under normal day-night conditions, as well as under the greater stress caused by continuous light. We determined that N 2 fixation cycled in continuous light but with a lower N 2 fixation activity. Glycogen degradation, respiration, and photosynthesis were also lower; nonetheless, O 2 evolution was about 50% of the normal peak. We also demonstrated that nifH (encoding the nitrogenase Fe protein), nifB, and nifX were strongly induced in continuous light; this is consistent with the role of these proteins during the assembly of the enzyme complex and suggested that the decreased N 2 fixation activity was due to protein-level regulation or inhibition. Many soluble electron carriers (e.g., ferredoxins), as well as redox carriers (e.g., thioredoxin and glutathione), were strongly induced during N 2 fixation in continuous light. We suggest that these carriers are required to enhance cyclic electron transport and phosphorylation for energy production and to maintain appropriate redox levels in the presence of elevated O 2 , respectively.

Genome-wide analysis of diel gene expression in the unicellular N2-fixing cyanobacterium Crocosphaera watsonii WH 8501

“…Crocosphaera diel gene expression T Shi et al expression profile and found to be under circadian control (Toepel et al, 2008). However, genes for DNA replication were not among the cycling genes in Cyanothece (Stöckel et al, 2008).…”

“…The expression of nitrogenase genes in Trichodesmium and in the intertidal or coastal marine unicellular cyanobacterium Cyanothece sp. strain 51142 has been shown to be under circadian control (Schneegurt et al, 1994;Chen et al, 1998;BermanFrank et al, 2001;Toepel et al, 2008). Genome-wide diel expression analysis may further elucidate the mechanism mediating the spatial/temporal segregation of oxygenic photosynthesis and N 2 fixation in diazotrophic cyanobacteria.…”

“…Recently, whole-genome expression in the closely related marine, but intertidal, unicellular cyanobacterium Cyanothece sp. ATCC 51142 (Cyanothece) was reported Toepel et al, 2008), making it possible to determine common features of genome expression in the unicellular N 2 -fixing cyanobacteria and to determine unique gene expression patterns of the open ocean species C. watsonii. In this paper, we report whole-genome expression patterns in the cultures of C. watsonii that were grown under alternating light-dark cycles and N 2 -fixing conditions.…”

In situ transcriptomic analysis of the globally important keystone N2-fixing taxon Crocosphaera watsonii

“…The nifB gene, which forms part of the nifBQ cluster and is necessary for the processing of the Fe-Mo cofactor encoded by nifHDK (Roberts et al, 1978), was also highly represented among the daytime transcripts, in line with expression observed in Cyanothece sp. ATCC 51142 (Toepel et al, 2008). Finally, a hypothetical protein flanked by nifZ and nifP (Cwat_DRAFT_3843) had the greatest number of transcripts; however, its function in nitrogenase is unknown and it may be an attractive target for expression studies.…”

“…In Cyanothece sp. ATCC 51142, differential expression of nitrogenase cluster genes occurs over diel cycles, with expression of some genes during the light, even though most genes are more highly expressed in the dark (Colon-Lopez and Sherman, 1998;Stoeckel et al, 2008;Toepel et al, 2008). The Fe-Mo structural protein nifK, which is encoded for by the nifHDK polycistronic mRNA (Chen et al, 1998), had almost as many transcripts represented as nifH, which is the gene commonly used to examine diazotroph abundance and nitrogenase expression in environmental samples (Church et al, 2005;Short and Zehr, 2007;Zehr et al, 2007b).…”