The Cyanobacterial Uptake Hydrogenase Regulation, Maturation and Function

Sammanfattning: With accellerating global warming and pollution problems a change of energy regime is necessary. Solar energy offers a clean and unlimited energy source of enormous potential. Due to it’s intermittenet nature solar energy must be stored - ideally in the chemical bond of a carrier molecule. Hydrogen gas, H2, an energy carrier with water as only emission when used in a fuel cell, is considered to be the choise for the future. In this context cyanobacteria show promising potential as future H2 factories since they can produce H2 from solar energy and water. The main enzymes directly involved in cyanobacterial hydrogen metabolism are nitrogenases and hydrogenases. Cyanobacterial hydrogenases are either uptake hydrogenases or bidirectional hydrogenases and their maturation requires assistance of six maturation proteins and two hydrogenase specific proteases. In this thesis the transcriptional regulation, maturation and function of the cyanobacterial uptake hydrogenases were investigated in the filamentous, heterocyst forming strains Nostoc punctiforme ATCC 29133 and Nostoc sp. strain PCC 7120. Five genes, encoding proteins putatively involved in the maturation of the uptake hydrogenase were identified upstream the known maturation genes. Two transcription factors, CalA and CalB, were found interacting with the stretch of DNA forming the upstream regions of the uptake hydrogenase structural genes and the novel maturation genes. The expression of the uptake hydrogenase were  heterocysts specific and the specificity mapped to a short promoter region starting -57 bp upstream the transcription start point. In addition, the function of the uptake hydrogenase was inserted in a metabolic context. Among the proteases, a conserved region was discovered possibly involved in determining the hydrogenase specificity. This thesis has given valuable information about the transcriptional regulation, maturation and function of the uptake hydrogenase in filamentous, heterocystous cyanobacteria and identified new targets for bioengineering of mutant strains with higher H2 production rates.