Phototaxis as a Collective Phenomenon in Cyanobacterial Colonies

Abstract

13Cyanobacteria are a widely distributed, diverse group of photosynthetic bacteria that exhibit 14 phototaxis, or motion in response to light. Cyanobacteria such as Synechocystis sp. secrete 15 a mixture of complex polysaccharides that facilitate cell motion, while their type 4 pili allow 16 them to physically attach to each other. Even though cells can respond individually to light, 17 colonies of such bacteria are observed to move collectively towards the light source in dense 18 finger-like projections. Agent-based models are especially useful in connecting individual cell 19 behaviour with the emergent collective phenomena that arise out of their interactions. We 20 present an agent-based model for cyanobacterial phototaxis that accounts for slime deposition 21 as well as for direct physical links between bacteria, mediated through their type 4 pili. 22 We reproduce the experimentally observed aggregation of cells at the colony boundary as a 23 precursor to finger formation. Our model also describes the changes in colony morphology 24 that occur when the location of the light source is abruptly changed. We find that the overall 25 motion of cells toward light remains relatively unimpaired even if a fraction of them do 26 not sense light, allowing heterogeneous populations to continue to mount a robust collective 27 response to stimuli. Our work suggests that in addition to bio-chemical signalling via diffusible 28 molecules in the context of bacterial quorum-sensing, short-ranged physical interactions may 29 also contribute to collective effects in bacterial motility.

Photocatalytic removal of the cyanobacterium Microcystis aeruginosa PCC7813 and four microcystins by TiO2 coated porous glass beads with UV-LED irradiation

“…Several design parameters have to be considered when applying immobilized TiO2 in a water treatment context. For example, cyanobacteria occupy different positions in the water column, depending on species and time of the day (Varuni et al, 2017). Thus, to ensure maximum efficiency of immobilized TiO2, an even distribution throughout the water column is desirable.…”

Apparent Phototaxis Enabled by Brownian Motion

“…[10,31,3,12] Even though a complete understanding of the different mechanisms and their implementations is still to be achieved, first agent based models describe phototactic behaviour, e.g. in colonies of cyanobacteria [27,33] or use mesoscale dynamics simulations to study the phototactic behavior of self-thermophoretic Janus particles. [35] First artificial creation of tactic behaviours mostly mimic photophobicity, i.e.…”