Better Living Through Cyanothece – Unicellular Diazotrophic Cyanobacteria with Highly Versatile Metabolic Systems
Cyanothece sp. ATCC 51142 is a unicellular, diazotrophic cyanobacterium with a versatile metabolism and very pronounced diurnal rhythms. Since nitrogen fixation is exquisitely sensitive to oxygen, Cyanotheceutilizes temporal regulation to accommodate these incompatible processes in a single cell. When grown under 12 h light–dark (LD) periods, it performs photosynthesis during the day and N2 fixation and respiration at night. Genome sequences of Cyanothece sp. ATCC 51142 and that of five other Cyanothece species have been completed and have produced some surprises. Analysis at both the transcriptomic and the proteomic levels in Cyanothece sp. ATCC 51142 has demonstrated the relationship of the metabolic synchrony with gene expression and has given us insights into diurnal and circadian regulation throughout a daily cycle. We are particularly interested in the regulation of metabolic processes, such as H2 evolution, and the way in which these organisms respond to environmental cues, such as light, the lack of combined nitrogen, and changing O2 levels. Cyanothece strains produce copious amounts of H2 under different types of physiological conditions. Nitrogenase produces far more H2 than the hydrogenase, in part because the nitrogenase levels are extremely high under N2-fixing conditions. With Cyanothece 51142 cultures grown in NO3-free media, either photoautotrophically or mixotrophically with glycerol, we have obtained H2 production rates over 150 μmol/mg Chl/h.
KeywordsNitrogen Fixation Hydrogen Production Linear Chromosome Mehler Reaction Uptake Hydrogenase
We would like to thank the many people who have been involved with this work, including those at the Washington University Genome Center and the W. R. Wiley Environmental Molecular Science Laboratory (EMSL) for work on proteomics, especially Jon M. Jacobs and Richard D. Smith. Special thanks goes to Eric Welsh of the Pakrasi Lab for all his efforts on the annotation of the Cyanothece 51142 genome. We would like to thank the following members of the Pakrasi Lab for figures: Michelle Liberton (Fig. 16.1), Eric Welsh (Fig. 16.2), and Anindita Banerjee (Fig. 16.3).
This work was supported by the Danforth Foundation at Washington University, a Department of Energy grant on hydrogen production, and by the Joint Genome Initiative. This work is also part of a Membrane Biology Scientific Grand Challenge project at the W. R. Wiley Environmental Molecular Science Laboratory, a national scientific user facility sponsored by the U.S. Department of Energy’s Office of Biological and Environmental Research program (Pacific Northwest National Laboratory).
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