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

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.

A bioactive molecule made by unusual salvage of radical SAM enzyme byproduct 5-deoxyadenosine blurs the boundary of primary and secondary metabolism

“…Although it is not obvious from isolated in vitro studies, we speculate that 7dSh might play a role in niche competition. In its natural environment, S. elongatus can live planktonically, but it is also able to form biofilms or microbial mats, which also contain the colonization of caves and humid stonewalls (46)(47)(48)(49)(50). In the latter habitats, the dilution of excreted compounds is prevented, and therefore, the activity of 7dSh as an allelopathic inhibitor is imaginable.…”

In vivo Inhibition of the 3-Dehydroquinate Synthase by 7-Deoxysedoheptulose Depends on Promiscuous Uptake by Sugar Transporters in Cyanobacteria

“…The main problem of allelopathic interactions in aquatic ecosystems is the dilution of the allelochemical, thereby causing a reduction of the effective concentrations ( Gross, 2003 ). Although S. elongatus was originally isolated from freshwater and is commonly cultivated in its planktonic lifestyle in the laboratory ( Golden, 2019 ), various authors reported that S. elongatus can also exhibit a terrestrial lifestyle, colonizing soil, rocks, humid stonewalls, and even caves in microbial mats and biofilms ( Schlösser, 1994 ; Czerwik-Marcinkowska and Mrozińska, 2011 ; Mattern and Mareš, 2018 ; Yang et al, 2018 ; Conradi et al, 2020 ). Although 7dSh is isolated from planktonic cells, we suggest that 7dSh as an allelopathic inhibitor might play a more important role in its terrestrial and community-/biofilm-forming lifestyle, where it accumulates in high concentrations.…”

Thermosynechococcus switches the direction of phototaxis by a c-di-GMP dependent process with high spatial resolution

“…S11). Such behaviour would lead to a dynamic circulation of Thermosynechococcus species inside a microbial mat under solar irradiance (43). The high light/short wavelength-induced downward migration and green light-induced upward migration of cyanobacteria in microbial mats are well documented (44)(45)(46)(47).…”