Photosynthetically-powered phototactic active nematic fluids and gels

TL;DR

This study explores how light gradients induce organized phototactic motion and self-assembly in cyanobacterial filaments, leading to active nematic states with complex defect structures, revealing new insights into ancient active matter.

Contribution

It demonstrates light-induced self-assembly of cyanobacterial active nematics and quantifies their dynamic transitions and defect formations, a novel exploration of photosynthetic active matter.

Findings

Light causes spontaneous formation of active nematic states.

Transitions between disordered and ordered phases are quantitatively characterized.

Patterned light and inclusions influence defect dynamics and interfacial behaviors.

Abstract

One of the most ancient forms of life dating to ~3.5 billion years ago, cyanobacteria are highly abundant organisms that convert light into energy and motion, often within conjoined filaments and larger colonies. We study how gradients of light intensity trigger orderly phototactic motions and dense bacterial communities, which remained quantitatively unexplored despite being among the oldest forms of active living matter on Earth. The phototaxis drives a transition from initially polar motions of semiflexible long filaments along complex curved spatiotemporal trajectories confined within illuminated areas to their bipolar motility in the ensuing crowded environment. We demonstrate how simply shining light causes a spontaneous self-assembly of two- and three-dimensional active nematic states of cyanobacterial filaments, with a plethora of motile and static topological defects. We quantify light-controlled evolutions of orientational and velocity order parameters during the transition between disordered and orientationally ordered states of our photosynthetic active matter, as well as the subsequent active nematic's fluid-gel transformation. Patterned illumination and foreign inclusions with different shapes interact with cyanobacterial active nematics in nontrivial ways, while inducing soft interfacial boundary conditions and quasi-boojum-like defects. Commanding this cyanobacterial collective behavior could aid inhibiting generation of toxins or enhancing production of oxygen and biomaterials.