The Role of the Cyanobacterial Type IV Pilus Machinery in Finding and Maintaining a Favourable Environment.

Fabian D Conradi,Conrad W Mullineaux,Annegret Wilde

doi:10.3390/life10110252

Fabian D Conradi, Conrad W Mullineaux + Show 1 more

Open Access

https://doi.org/10.3390/life10110252

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Abstract

Type IV pili (T4P) are proteinaceous filaments found on the cell surface of many prokaryotic organisms and convey twitching motility through their extension/retraction cycles, moving cells across surfaces. In cyanobacteria, twitching motility is the sole mode of motility properly characterised to date and is the means by which cells perform phototaxis, the movement towards and away from directional light sources. The wavelength and intensity of the light source determine the direction of movement and, sometimes in concert with nutrient conditions, act as signals for some cyanobacteria to form mucoid multicellular assemblages. Formation of such aggregates or flocs represents an acclimation strategy to unfavourable environmental conditions and stresses, such as harmful light conditions or predation. T4P are also involved in natural transformation by exogenous DNA, secretion processes, and in cellular adaptation and survival strategies, further cementing the role of cell surface appendages. In this way, cyanobacteria are finely tuned by external stimuli to either escape unfavourable environmental conditions via phototaxis, exchange genetic material, and to modify their surroundings to fit their needs by forming multicellular assemblies.

Highlights

The Type IV Pilus Machinery Conveys Twitching Motility to CyanobacteriaCyanobacteria are found in a wide variety of ecological niches, ranging from polar latitudes [1,2]
Cyanobacteria are finely tuned by external stimuli to either escape unfavourable environmental conditions via phototaxis, exchange genetic material, and to modify their surroundings to fit their needs by forming multicellular assemblies
Cyanobacteria are not known to possess flagella and instead, most motile cyanobacteria rely on T4P to convey twitching motility across surfaces, allowing them to move towards favourable environments or to escape unfavourable environments

Summary

The Type IV Pilus Machinery Conveys Twitching Motility to Cyanobacteria

Cyanobacteria are found in a wide variety of ecological niches, ranging from polar latitudes [1,2]. PCC 6803 (hereafter Synechocystis), but other instances have been reported and characterised in both single-celled [5] and filamentous cyanobacteria [6], which largely match the Synechocystis T4P machinery in component genes and operon structure [7]. In Synechocystis, the components of the T4P complex have been largely identified by homology with the Type. The filamentous cyanobacterium Nostoc punctiforme contains multiple PilA-like proteins and many of the components of the N. punctiforme T4P machinery have been identified according to Synechocystis annotations [19]. A set of accessory proteins have been identified in Synechocystis by homology with heterotrophic T4P systems, termed. The alignment complex composed of the PilMNOP accessory proteins forms a set of two rings in the periplasmic space [12] and links the T4P apparatus components in the inner and outer membranes. In contrast to Synechocystis, only thick pili have been detected in Nostoc hormogonia [19]

Twitching Motility Enables Cyanobacteria to Seek out Favourable and Escape

Many Species of Cyanobacteria Form Large-Scale Multicellular Assemblages

The T4P Apparatus Has Structural and Secretory Roles in Cyanobacterial

Regulation of the T4P Machinery

Cyanobacterial Natural Competence Requires T4P

Concluding Remarks