Roles of Close Homologues SigB and SigD in Heat and High Light Acclimation of the Cyanobacterium Synechocystis sp. PCC 6803.

Otso Turunen,Taina Tyystjärvi,Satu Koskinen,Juha Kurkela,Kaisa Hakkila,Outi Karhuvaara

doi:10.3390/life12020162

Abstract

Acclimation of cyanobacterium Synechocystis sp. PCC6803 to suboptimal conditions is largely dependent on adjustments of gene expression, which is highly controlled by the σ factor subunits of RNA polymerase (RNAP). The SigB and SigD σ factors are close homologues. Here we show that the sigB and sigD genes are both induced in high light and heat stresses. Comparison of transcriptomes of the control strain (CS), ΔsigB, ΔsigD, ΔsigBCE (containing SigD as the only functional group 2 σ factor), and ΔsigCDE (SigB as the only functional group 2 σ factor) strains in standard, high light, and high temperature conditions revealed that the SigB and SigD factors regulate different sets of genes and SigB and SigD regulons are highly dependent on stress conditions. The SigB regulon is bigger than the SigD regulon at high temperature, whereas, in high light, the SigD regulon is bigger than the SigB regulon. Furthermore, our results show that favoring the SigB or SigD factor by deleting other group 2 σ factors does not lead to superior acclimation to high light or high temperature, indicating that all group 2 σ factors play roles in the acclimation processes.

Highlights

Efficient recycling and sustainable production of valuable compounds are major challenges of the future
The predicted promoter regions of sigB and sigD genes were cloned in front of the luxCDABE operon from Photorhabdus luminescens, and the non-essential psbA1 gene was replaced from Synechocystis genome with these constructs to produce PsigB- and PsigD-lux strains (Figure 1A–C)
Luminescence levels remained low in PsigB- and PsigD-lux strains in standard growth conditions (Figure 1D)

Summary

Introduction

Efficient recycling and sustainable production of valuable compounds are major challenges of the future. Piggery, and dairy wastewaters, as well as anaerobic digestion reject waters, are typically nutrient rich, containing plenty of ammonium, nitrate, and phosphate [1,2]. Cyanobacteria are efficient in collecting nutrients [3] and many valuable products, including ethanol, isopropanol, butanol, biohydrogen and alkanes, have already been produced in cyanobacteria [4]. In the most tempting scenario, cyanobacteria are engineered to produce high value compounds, biomass, and simultaneously remediate wastewaters. Keeping up constant optimal environmental conditions, such as optimal temperature and constant light, is expensive, and using wastewater as a growth medium might cause additional problems; wastewaters typically contain harmful chemicals, and their nutrient balance is variable and not optimal

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