PT  - JOURNAL ARTICLE
AU  - P. Varuni
AU  - Shakti N. Menon
AU  - Gautam I. Menon
TI  - Modelling Phototaxis as a Collective Phenomenon in Cyanobacterial Colonies
AID  - 10.1101/155622
DP  - 2017 Jan 01
TA  - bioRxiv
PG  - 155622
4099  - http://biorxiv.org/content/early/2017/06/26/155622.short
4100  - http://biorxiv.org/content/early/2017/06/26/155622.full
AB  - Micro-organisms respond to a variety of stimuli, including chemical concentrations, osmolarity and light. Cyanobacteria are a widely distributed, diverse group of photosynthetic bacteria that exhibit phototaxis, or motion in response to light. In the cyanobacterium Synechocystis sp., dense finger-like projections of cells emerging from a colony move towards or away from light, while the cells lay down a mixture of complex polysaccharides (‘slime’) which locally facilitates their motion. Although cells can respond individually to light, they are observed to aggregate at the colony edge before forming finger-like projections. Such collective behaviour is likely to be mediated through Type 4 Pili (T4P) that can allow cells to attach to each other. We present a model for cyanobacterial phototaxis where cells can sense a light source and move towards it while depositing slime. The action of T4P is modelled in terms of the forces the attached cells exert on each other. Our model reproduces many experimentally observed patterns of collective phototaxis, including the response to a change in position of the light source. We show that a consequence of this kind of collective phototaxis is that the overall motion of cells toward light is relatively unimpaired even if a fraction of them do not sense light.