Control of Hormogonium Differentiation in the Symbiotic Cyanobacterium Nostoc Punctiforme

University Of California-Davis, Davis CA

Investigators

Abstract

0080805 Meeks The nitrogen-fixing cyanobacterium Nostoc punctiforme exemplifies filamentous cyanobacteria (blue-green algae) whose vegetative cells have four developmental alternatives and are the most complex of all bacteria. Depending on the environmental conditions vegetative cells can: grow and divide to continue the vegetative growth cycle, transiently differentiate into motile filaments called hormogonia, transiently differentiate into resting cells called akinetes, or terminally differentiate into heterocysts, the sites of nitrogen fixation. This project focuses on identifying the regulatory mechanisms involved in hormogonium differentiation and behavior. Motile hormogonium filaments serve in the colonization of new habitats and as the infective units in establishment of symbiotic associations with plants and fungi by the Nostoc. Cyanobacteria are important producers of reduced carbon and nitrogen for other organisms in maintaining steady state environmental conditions. In symbiotic associations with lichens for example, nitrogen-fixing cyanobacteria contribute to the consumption of atmospheric carbon dioxide in poor soils and lessen the extent of global warming. This project has two overall objectives. 1. Determine the extent of differential gene expression during hormogonium differentiation, using two dimensional protein gel electrophoresis to identify differentially synthesized proteins, determine the amino acid sequence of selected proteins and use the N. punctiforme genome data base to identify the corresponding genes that encode the proteins. 2. Characterization of a set of genes, whose synthesized proteins may function in the production of a metabolic compound that represses hormogonium differentiation. Specific focus will be on the activity of the hypothetical transcriptional repressor of the genes. The results of this study will be of value in addressing questions of the hierarchy, integration and evolution of regulatory pathways in developmental biology using