Collective Behaviour of Filamentous Cyanobacteria

by Antaran Kumar Deka
Doctoral thesis
Date of Examination:2023-05-25
Date of issue:2024-01-11
Advisor:Dr. Stefan Karpitschka
Referee:Prof. Dr. Stefan Klumpp
Referee:Prof. Dr. Jörg Enderlein
Persistent Address: http://dx.doi.org/10.53846/goediss-10286

 

 

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Abstract

English

Cyanobacteria are the oldest phototrophic organisms on the planet. Having been responsible for the “Great Oxidation Event” millions of years ago, it has enabled the development and sustenance of multi-cellular life forms, as we witness it today. Today they are abundant in many eco-systems, forming dense suspended colonies or mats which sometimes poses serious economical and ecological threats. Structural patterns in these mats are dynamic and adaptive according to environment they thrive in, thereby enhancing their capability of acclimatization. These microbial mats involve the interaction of long, flexible multi-cellular cyanobacterial filaments which tends to glide over substrates. However, neither micro-mechanics nor the pattern formation mechanism has been investigated so far. We investigate the behaviour of two filamentous species of cyanobacteria: Oscillatoria lutea and Kamptonema animale that are characterized by high flexibility, aspect ratio and direction reversals. We successfully calibrate the bending rigidity of the two species using micro-pipette force sensor and quantify their active gliding forces using a modified Euler self-buckling theory. We then study the collective behaviour of the two species in a system of reduced complexity by confining them between agar and a glass bottom petri-dish. We analyze the spatial correlations of density, polar and nematic order parameters with respect to length and speed distribution and the reversal rates. We find that longer filaments have higher propensity to form spiral structures and shorter filaments have higher tendency to glide in the direction of their neighbours. No significant correlations are observed with the speed of gliding. We also find that direct neighbour polar correlation goes up with a decrease in the delay time between reversals. This enhancement of reversal rate by polarity can be attributed to a responsive, possibly mechano-sensing based reversal mechanism rather than a completely random one.
Keywords: Cyanobacteria; Micropipette Force Sensor; Bending Stiffness; Collective Motion; Direction Reversals
 
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