Sean Callahan

Professor and Associate Chair

Prokaryotic Biology; "Fixation" of Biologically Inert Dinitrogen Gas and Specialized Cells Along a Filament



Sny 201


(808) 956-8015


(808) 956-5339

Research Interests

We focus on two basic areas of prokaryotic biology. The first involves the “fixation” of biologically inert dinitrogen gas to a form that can be used by organisms for growth, in this case ammonia. As an integral part of the earth’s nitrogen cycle, this process is necessary for life as we know it. The laboratory uses modern molecular genetics to study the physiology of nitrogen fixation by cyanobacteria, photosynthetic, filamentous bacteria that form specialized cells called heterocysts, the sites of nitrogen fixation. The second area of research focuses on the pattern of these specialized cells along a filament. When these cyanobacteria are grown with fixed nitrogen, only one type of cell is present in the filament, but when the organism is starved for nitrogen, every tenth cell differentiates into a nitrogen-fixing heterocyst. This process illustrates the fundamental question of development: how can a non-random pattern of different cell-types form from a seemingly equivalent group of cells? The laboratory is investigating the roles and interactions between genes that are known to influence pattern formation while also identifying additional developmental genes.