patD , a Gene Regulated by NtcA, Is Involved in the Optimization of Heterocyst Frequency in the Cyanobacterium Anabaena sp. Strain PCC 7120

Abstract

In the filamentous multicellular cyanobacterium Anabaena sp. strain PCC 7120, 5 to 10% of the cells differentiate into heterocysts, which are specialized in N2 fixation. Heterocysts and vegetative cells are mutually dependent for filament growth through nutrient exchange. Thus, the heterocyst frequency should be optimized to maintain the cellular carbon and nitrogen (C/N) balance for filament fitness in the environment. Here, we report the identification of patD, whose expression is directly activated in developing cells by the transcription factor NtcA. The inactivation of patD increases heterocyst frequency and promotes the upregulation of the positive regulator of heterocyst development hetR, whereas its overexpression decreases the heterocyst frequency. The change in heterocyst frequency resulting from the inactivation of patD leads to the reduction in competitiveness of the filaments under combined-nitrogen-depleted conditions. These results indicate that patD regulates heterocyst frequency in Anabaena sp. PCC 7120, ensuring its optimal filament growth. IMPORTANCE Microorganisms have evolved various strategies in order to adapt to the environment and compete with other organisms. Heterocyst differentiation is a prokaryotic model for studying complex cellular regulation. The NtcA-regulated gene patD controls the ratio of heterocysts relative to vegetative cells on the filaments of Anabaena sp. strain PCC 7120. Such a regulation provides a mechanism through which carbon fixation by vegetative cells and nitrogen fixation by heterocysts are properly balanced to ensure optimal growth and keep a competitive edge for long-term survival.

The developmental regulator PatD modulates assembly of the cell‐division protein FtsZ in the cyanobacterium Anabaena sp. PCC 7120

“…These observations indicate that heterocysts of the patD mutant present activity of septal PG synthesis, which is absent from wild-type heterocysts. Considering that in the wild-type PatD accumulates in the heterocysts (Wang et al, 2019), these results suggest that during heterocyst differentiation PatD contributes to abolish late divisome activity, whereas at least some activity is preserved in the absence of PatD.…”

“…To test PatD–FtsZ interactions in vivo , we expressed in Anabaena a recombinant version of PatD linked to a StrepTag and GFP or, as a control, a StrepTag‐GFP alone (see Experimental procedures). The Strep tagged and GFP fused PatD was functional since it was able to reduce heterocyst frequency to 2.8% when present on a replicative plasmid, as reported for patD (Wang et al ., 2019). Total proteins were extracted from each strain and passed through a Strep‐Tag‐affinity column.…”

Influence of Mo and Fe on Photosynthetic and Nitrogenase Activities of Nitrogen-Fixing Cyanobacteria under Nitrogen Starvation

“…Thus, the NtcA-regulated pat D gene is reported to control the ratio of heterocysts relative to vegetative cells on the filaments of Anabaena sp. PCC 7120 [ 53 ]. It should be noted that according to our results, the frequency of heterocyst formation was even significantly higher under nitrogen deficiency in the medium in some strains.…”

Transcriptome Analysis Reveals IsiA-Regulatory Mechanisms Underlying Iron Depletion and Oxidative-Stress Acclimation in Synechocystis sp. Strain PCC 6803

“…RNA-seq analysis was implemented using cultures at ϪFe/ϪMV (iron-depleted) and ϪFe/ϩMV (iron depleted-MV treated) with three biological replicates. The WT strain and ΔisiA mutant were cultured in iron-depleted media for 24 h; then 5 M MV was added to the culture to be harvested for 4 h. Total cellular RNA was extracted using TRIzol reagent (Invitrogen, USA) according to a method that was previously described (53). RNA quality was assessed using the Nanodrop 2000 (Thermo Fisher Scientific).…”