C-di-GMP Homeostasis Is Critical for Heterocyst Development in Anabaena sp. PCC 7120.

Min Huang,Xiaoli Zeng,Cheng-Cai Zhang,Ju-Yuan Zhang

doi:10.3389/fmicb.2021.793336

Abstract

c-di-GMP is a ubiquitous bacterial signal regulating various physiological process. Anabaena PCC 7120 (Anabaena) is a filamentous cyanobacterium able to form regularly-spaced heterocysts for nitrogen fixation, in response to combined-nitrogen deprivation in 24h. Anabaena possesses 16 genes encoding proteins for c-di-GMP metabolism, and their functions are poorly characterized, except all2874 (cdgS) whose deletion causes a decrease in heterocyst frequency 48h after nitrogen starvation. We demonstrated here that c-di-GMP levels increased significantly in Anabaena after combined-nitrogen starvation. By inactivating each of the 16 genes, we found that the deletion of all1175 (cdgSH) led to an increase of heterocyst frequency 24h after nitrogen stepdown. A double mutant ΔcdgSHΔcdgS had an additive effect over the single mutants in regulating heterocyst frequency, indicating that the two genes acted at different time points for heterocyst spacing. Biochemical and genetic data further showed that the functions of CdgSH and CdgS in the setup or maintenance of heterocyst frequency depended on their opposing effects on the intracellular levels of c-di-GMP. Finally, we demonstrated that heterocyst differentiation was completely inhibited when c-di-GMP levels became too high or too low. Together, these results indicate that the homeostasis of c-di-GMP level is important for heterocyst differentiation in Anabaena.

Highlights

Cyclic nucleotides act as second messengers in all domains of life (Tschowri et al, 2014)
We demonstrated that heterocyst differentiation was completely inhibited when c-di-GMP levels became too high or too low. These results indicate that the homeostasis of c-di-GMP level is important for heterocyst differentiation in Anabaena
Heterocyst differentiation in cyanobacteria is regulated by multiple signals (Zhang et al, 2006)

Summary

INTRODUCTION

Cyclic nucleotides act as second messengers in all domains of life (Tschowri et al, 2014). Subsequent studies have revealed that c-di-GMP regulates a variety of important cellular processes, including biofilm formation, motility, virulence, cell differentiation, cell cycle and mechanical sensing (Tischler and Camilli, 2004; Kulesekara et al, 2006; Hengge, 2009; Boehm et al, 2010; Romling et al, 2013; Tschowri et al, 2014; Lori et al, 2015; Hug et al, 2017; Xu et al, 2019; Del Medico et al, 2020; Snyder et al, 2020) Such regulations may c-di-GMP Regulates Heterocyst Development in Anabaena take place at the transcriptional, post-transcriptional, or posttranslational levels by interacting with different types of effectors (Romling et al, 2013; Chou and Galperin, 2016). This study paves the way for characterizing the signalling function of c-di-GMP in this cyanobacterium, a model for prokaryotic development

MATERIALS AND METHODS

RESULTS

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DISCUSSION