Minor pilins are involved in motility and natural competence in the cyanobacterium Synechocystis sp. PCC 6803

Abstract

Cyanobacteria synthesize type IV pili, which are known to be essential for motility, adhesion and natural competence. They consist of long flexible fibers that are primarily composed of the major pilin PilA1 in Synechocystis sp. PCC 6803. In addition, Synechocystis encodes less abundant pilin‐like proteins, which are known as minor pilins. In this study, we show that the minor pilin PilA5 is essential for natural transformation but is dispensable for motility and flocculation. In contrast, a set of minor pilins encoded by the pilA9‐slr2019 transcriptional unit are necessary for motility but are dispensable for natural transformation. Neither pilA5‐pilA6 nor pilA9‐slr2019 are essential for pilus assembly as mutant strains showed type IV pili on the cell surface. Three further gene products with similarity to PilX‐like minor pilins have a function in flocculation of Synechocystis. The results of our study indicate that different minor pilins facilitate distinct pilus functions. Further, our microarray analysis demonstrated that the transcription levels of the minor pilin genes change in response to surface contact. A total of 122 genes were determined to have altered transcription between planktonic and surface growth, including several plasmid genes which are involved exopolysaccharide synthesis and the formation of bloom‐like aggregates.

The genome sequence of Synechocystis sp. PCC 6803 substrain GT‐T and its implications for the evolution of PCC 6803 substrains

“…1D,E ) or GT‐P [ 30 ] but differ from the motile PCC‐M substrain (Fig. 1F,H ; for motile strains see also [ 29 , 31 ]). The GT‐T, GT‐W, and GT‐P substrains display thin pili and thin pili bundles but lack typical type IV thick pili in contrast to the motile substrains.…”

Impairment of a cyanobacterial glycosyltransferase that modifies a pilin results in biofilm development

“…S. elongatus possesses several pilA candidate genes: synpcc7942_0049/0048, Synpcc7942_2479, Synpcc7942_2482, Synpcc7942_2484, Synpcc7942_2485, Synpcc7942_2590 and Synpcc7942_2591. It is possible that, as proposed for other organisms (Muschiol et al ., 2015 ; Neuhaus et al ., 2020 ; Oeser et al ., 2021 ), only particular pili serve in DNA uptake by S . elongatus , and ogt inactivation may not affect the assembly of competence pili.…”

Development of a Highly Sensitive Luciferase-Based Reporter System To Study Two-Step Protein Secretion in Cyanobacteria

“…It binds to the pilus base via the C-terminus of the extension ATPase PilB1. Δhfq mutants are non-motile, not naturally competent, lack thick pili but retain thin pili (12,27,29). Therefore, we hypothesized that, if the T4aPS was involved in the secretion of non-pilin proteins, the Δhfq mutant would show impaired secretion.…”

“…The cyanobacterial T4aPS consists of several highly conserved core units: a retractable pilus fiber, mainly constituted of the major pilin PilA, an assembly platform (PilC), ATPases that extend (PilB) and retract (PilT) the pilus fiber, an outer membrane pore through which the pilus fiber extends (PilQ), a bifunctional peptidase/methylase (PilD) that cleaves the signal peptide of nascent pilins and a complex that aligns the pilus fiber through the periplasm (PilMNOP). Cyanobacteria also encode several minor pilins that play a role in natural transformation and aggregation and may be incorporated as components of the pilus fiber (11,12). The T4aPS is evolutionarily, structurally and functionally similar to bacterial type II secretion systems (T2SS) (13,14).…”