Date of Award


Document Type


Degree Name

Master of Science (M.S.)


Biological Sciences

First Advisor

Doug Risser

First Committee Member

Lisa A. Wrischnik

Second Committee Member

Geoffrey Lin-Cereghino


Cyanobacteria are prokaryotes capable of oxygenic photosynthesis, and for many species, nitrogen fixation, giving cyanobacteria an important role in global carbon and nitrogen cycles. Furthermore, multicellular filamentous cyanobacteria are developmentally complex, capable of differentiation into different cell types, including cells capable of nitrogen fixation and cells for motility, making them an ideal platform for studying development, as well as for practical use in biotechnology. Understanding how developmental programmes are activated require an understanding of the role of alternative sigma factors, which are required for transcriptional activation in bacteria. In order to investigate the gene regulatory network and to determine the role of alternative sigma factors in hormogonium development, real time PCR and Next Generation RNA-seq were used to measure expression levels of genes involved in hormogonium development and to further characterise the nature of the hormogonium developmental programme in the filamentous cyanobacterium Nostoc punctiforme. The results support a model where a hierarchal sigma factor cascade activates hormogonium development, in which expression of sigJ activates expression of the sigma factors sigC and sigF, as well as a wide range of other genes, including those involved in the type IV pilus (T4P), chemotaxis-like systems, and cell architecture. SigC and SigF have more limited roles: cell division genes are dependent on SigC and pilA expression was stringently SigF-dependent. Interestingly, SigC was also found to enhance expression of sigJ during hormogonium development, implying a potential positive feedback loop between sigJ and sigC.



Included in

Biology Commons



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