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Background   Lyngbya majuscula  CCAP 1446/4 is a N 2 -fixing filamentous nonheterocystous strain that contains two NiFe-hydrogenases: an uptake (encoded by  hupSL ) and a bidirectional enzyme (encoded by  hoxEFUYH ). The biosynthesis/maturation of NiFe-hydrogenases is a complex process requiring several accessory proteins for e.g. for the incorporation of metals and ligands in the active center (large subunit), and the insertion of the FeS clusters (small subunit). The last step in the maturation of the large subunit is the cleavage of a C-terminal peptide from its precursor by a specific endopeptidase. Subsequently, the mature large and small subunits can assemble forming a functional enzyme.    Results  In this work we demonstrated that, in  L. majuscula , the structural genes encoding the bidirectional hydrogenase are cotranscribed, and that  hoxW  (the gene encoding its putative specific endopeptidase) is in the same chromosomal region but transcribed from a different promoter. The gene encoding the putative specific uptake hydrogenase endopeptidase,  hupW , can be cotranscribed with the structural genes but it has its own promoter.  hoxH ,  hupL ,  hoxW  and  hupW  transcription was followed in  L. majuscula  cells grown under N 2 -fixing and non-N 2 -fixing conditions over a 12 h light/12 h dark cycle. The transcription of  hoxH ,  hoxW  and  hupW  did not vary remarkably in the conditions tested, while the  hupL  transcript levels are significantly higher under N 2 -fixing conditions with a peak occurring in the transition between the light and the dark phase. Furthermore, the putative endopeptidases transcript levels, in particular  hoxW , are lower than those of the respective hydrogenase structural genes.    Conclusion  The data presented here indicate that in  L. majuscula  the genes encoding the putative hydrogenases specific endopeptidases,  hoxW  and  hupW , are transcribed from their own promoters. Their transcript levels do not vary notably in the conditions tested, suggesting that HoxW and HupW are probably constantly present and available in the cells. These results, together with the fact that the putative endopeptidases transcript levels, in particular for  hoxW , are lower than those of the structural genes, imply that the activity of the hydrogenases is mainly correlated to the transcription levels of the structural genes. The analysis of the promoter regions indicates that  hupL  and  hupW  might be under the control of different transcription factor(s), while both  hoxH  and  xisH  ( hoxW ) promoters could be under the control of LexA.

Transcription profiles of hydrogenases related genes in the cyanobacterium Lyngbya majuscula CCAP 1446/4