ART investigates aggregation in Trichodesmium with nanothechnology and molecular techniques

PI Mar Benavides

Partners Félix Rico and Marta Sebastián

Marine primary production is limited by nitrogen which enters the ocean mainly (~40-70%) through the fixation of dinitrogen (N2) by marine microbes called “diazotrophs”. The filamentous cyanobacterium Trichodesmium is the most active diazotroph in the ocean, sustaining up to 50% of primary production. Trichodesmium filaments tend to aggregate forming colonies of hundreds of filaments, but the processes driving this aggregation are unknown. When facing iron and/or phosphorus deficiency Trichodesmium releases extracellular polysaccharides. This material surrounds the cells forming an extracellular matrix (ECM), which could serve as a “natural glue” that sticks filaments together.

Filament aggregation may confer several competitive advantages to Trichodesmium, including a defense against predation or viral attack, desiccation, higher affinity for nutrients and a suitable structure for mutualistic epibiont bacterial colonization. Hence, ECM formation and filament aggregation likely respond to changes in Trichodesmium’s physiological status and the environmental conditions they face. The cellular mechanisms that induce filament aggregation in Trichodesmium filaments need to be understood, as they drive their population dynamics and ultimately fixed nitrogen inputs to the ocean. 

The ART project will apply a multidisciplinary approach combining the disciplines of microbial oceanography, molecular biology, nanotechnology and biophysics to investigate the mechanics and gene expression patterns of Trichodesmium under different nutrient regimes.

Trichodesmium filaments tend to aggregate forming colonies of hundreds of filaments, but the processes driving this aggregation are unknown. When facing iron and/or phosphorus deficiency Trichodesmium releases extracellular polysaccharides. This material surrounds the cells forming an extracellular matrix (ECM), which could serve as a “natural glue” that sticks filaments together.

The cellular mechanisms that induce filament aggregation in Trichodesmium filaments need to be understood, as they drive their population dynamics and ultimately fixed nitrogen inputs to the ocean. 

In preliminary tests on Trichodesmium cultures in collaboration with the Force Microscopy Lab we observed the topography of Trichodesmium filaments (Fig. 1A), identifying the network of organic matter (Fig. 1B). Force mapping revealed heterogeneous elasticity across the network surface (Fig. 1C) as quantified by the force curves (examples in Fig. 1D).