title: 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 approximately 10% 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.
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA.
authors.forename: Jörg
authors.initials: J
authors.lastname: Toepel
authors.forename: Eric
authors.initials: E
authors.lastname: Welsh
authors.forename: Tina C
authors.initials: TC
authors.lastname: Summerfield
authors.forename: Himadri B
authors.initials: HB
authors.lastname: Pakrasi
authors.forename: Louis A
authors.initials: LA
authors.lastname: Sherman
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D002940:Circadian Rhythm; D046889:Cyanothece / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology*; D006003:Glycogen / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D008027:Light; D009586:Nitrogen Fixation / Q000502:physiology; D009591:Nitrogenase / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D010101:Oxygen Consumption; D017440:Photoperiod; D010788:Photosynthesis / Q000502:physiology; D040081:Protein Array Analysis; D013997:Time Factors; D014158:Transcription, Genetic / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; C092498:NifB protein, Bacteria; C118795:NifX protein, Bacteria; D006003:Glycogen; D010088:Oxidoreductases; D009591:Nitrogenase; C029130:nitrogenase reductase