Recent Advances in Phototrophic Prokaryotes

Louis A. Sherman, Hongtao Min, Jörg Toepel, Himadri B. Pakrasi, Sherman, Louis A., Min, Hongtao, Toepel, Jörg, Pakrasi, Himadri B.

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 N(2) 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 H(2) evolution, and the way in which these organisms respond to environmental cues, such as light, the lack of combined nitrogen, and changing O(2) levels. Cyanothece strains produce copious amounts of H(2) under different types of physiological conditions. Nitrogenase produces far more H(2) than the hydrogenase, in part because the nitrogenase levels are extremely high under N(2)-fixing conditions. With Cyanothece 51142 cultures grown in NO(3)-free media, either photoautotrophically or mixotrophically with glycerol, we have obtained H(2) production rates over 150 mumol/mg Chl/h.