Like most cyanobacteria, Trichodesmium has a gram negative cell wall. However, unlike other aerobic diazotrophs, heterocysts (structures found in cyanobacteria which protect nitrogenase from oxygenation) are lacking in Trichodesmium. This is a unique characteristic among aerobic diazotrophs which fix nitrogen in daylight. Photosynthesis occurs using phycoerythrin - light-harvesting phycobiliprotein which is normally found within heterocysts in other diazotrophs.
