ZipN is an essential FtsZ membrane tether and contributes to the septal localization of SepJ in the filamentous cyanobacterium Anabaena

Sergio Camargo,Ana Valladares,Silvia Picossi,Sergio Arévalo,Antonia Herrero,Laura Corrales-Guerrero

doi:10.1038/s41598-019-39336-6

Abstract

The organismic unit of heterocyst-forming cyanobacteria is a filament of communicating cells connected by septal junctions, proteinaceous structures bridging the cytoplasms of contiguous cells. This distinct bacterial organization is preserved during cell division. In Anabaena, deletion of the zipN gene could not be segregated. We generated strain CSL109 that expresses zipN from a synthetic regulatable promoter. Under conditions of ZipN depletion, cells progressively enlarged, reflecting restricted cell division, and showed drastic morphological alterations including cell detachment from the filaments, to finish lysing. In contrast to the wild-type localization in midcell Z-rings, FtsZ was found in delocalized aggregates in strain CSL109. Consistently, the proportion of membrane-associated to soluble FtsZ in fractionated cell extracts was lower in CSL109. Bacterial two-hybrid analysis showed that ZipN interacts with FtsZ and other cell-division proteins including cytoplasmic Ftn6 and SepF, and polytopic FtsW, FtsX, FtsQ and FtsI. Additionally, ZipN interacted with the septal protein SepJ, and in CSL109 depletion of ZipN was concomitant with a progressive loss of septal specificity of SepJ. Thus, in Anabaena ZipN represents an essential FtsZ membrane tether and an organizer of the divisome, and it contributes to the conformation of septal structures for filament integrity and intercellular communication.

Highlights

Cyanobacteria are characterized by a phototrophic mode of life relying on oxygenic photosynthesis
Similar amounts of all2706 transcripts were detected by semi-quantitative RT-PCR analysis with RNA isolated from Anabaena and strain CSL109 (Fig. 1d), the latter being altered in expression of zipN. zipN encodes a 798-residue protein that was reported to include an N-terminal DnaJ domain[20]
In the presence of ammonium, expression of the gene in strain CSL109 is much lower than in the wild type and, under this condition, strain CSL109 shows a drastic increase in cell size concomitant with changes in cell shape

Summary

Introduction

Cyanobacteria are characterized by a phototrophic mode of life relying on oxygenic photosynthesis. SepJ has been considered to represent a structural component or organizer of septal complexes (known as septal junctions)[3,7] that would expand the intercellular periplasmic regions providing cell-to-cell adhesion and communication throughout the filament[7,8].The cyanobacterial filament grows by intercalary cell division and reproduces by random trichome breakage, and in strains such as www.nature.com/scientificreports/. Www.nature.com/scientificreports those of the genus Anabaena that produces unbranched filaments, the division plane is always perpendicular to the long filament axis[9] This distinct biological organization must include cell division mechanisms different from those present in the more common bacteria producing separated daughter cells[3]. Strain PCC 7120 the septal protein SepJ has been shown to interact with the divisome during cell division[24]. ZipN contributes to the septal localization of SepJ, which is required for filament integrity and intercellular communication in the filament

Methods

Results

Conclusion