Synechococcus sp. Strain PCC 7002 Transcriptome: Acclimation to Temperature, Salinity, Oxidative Stress, and Mixotrophic Growth Conditions

Abstract

Synechococcus sp. strain PCC 7002 is a unicellular, euryhaline cyanobacterium. It is a model organism for studies of cyanobacterial metabolism and has great potential for biotechnological applications. It exhibits an exceptional tolerance of high-light irradiation and shows very rapid growth. The habitats from which this and closely related strains were isolated are subject to changes in several environmental factors, including light, nutrient supply, temperature, and salinity. In this study global transcriptome profiling via RNAseq has been used to perform a comparative and integrated study of global changes in cells grown at different temperatures, at different salinities, and under mixotrophic conditions, when a metabolizable organic carbon source was present. Furthermore, the transcriptomes were investigated for cells that were subjected to a heat shock and that were exposed to oxidative stress. Lower growth temperatures caused relatively minor changes of the transcriptome; the most prominent changes affected fatty acid desaturases. A heat shock caused severe changes of the transcriptome pattern; transcripts for genes associated with major metabolic pathways declined and those for different chaperones increased dramatically. Oxidative stress, however, left the transcript pattern almost unaffected. When grown at high salinity, Synechococcus sp. PCC 7002 had increased expression of genes involved in compatible solute biosynthesis and showed increased mRNA levels for several genes involved in electron transport. Transcripts of two adjacent genes dramatically increased upon growth at high salinity; the respective proteins are putatively involved in coping with oxidative stress and in triggering ion channels. Only minor changes were observed when cells were grown at low salinity or when the growth medium was supplemented with glycerol. However, the transcriptome data suggest that cells must acclimate to excess reducing equivalents when a reduced C-source is present.

A Desaturase Gene Involved in the Formation of 1,14-Nonadecadiene in Synechococcus sp. Strain PCC 7002

“…It is known that upon a downshift in temperature, expression of some desaturases is upregulated and the mRNA stability of desaturase genes is altered (22), resulting in an increase of the unsaturated lipids that are used to maintain membrane fluidity at low temperatures. In the case of desE, global transcriptome profiling via RNA-seq showed that its transcript levels increased approximately 2-fold in cells grown at 22°C compared to cells grown at 38°C (28). Also, it has been shown that desE transcripts had an estimated half-life of only 1 min at 38°C and 21 min at 22°C (25), suggesting that desE is regulated to respond to changes in temperature.…”

Integrated Transcriptomic and Proteomic Analysis of the Global Response of Synechococcus to High Light Stress*

“…Sample Preparation-Synechococcus 7002 cells were grown in culture tubes (⌽40 mm ϫ 200 mm) containing medium A supplemented with 1 mg/ml NaNO 3 as nitrogen source (15,24). The cultures were grown at 38°C at 250 mol photons m Ϫ2 s Ϫ1 and were bubbled with 1% (v/v) CO 2 in air.…”

ChlR Protein of Synechococcus sp. PCC 7002 Is a Transcription Activator That Uses an Oxygen-sensitive [4Fe-4S] Cluster to Control Genes involved in Pigment Biosynthesis

“…Sequences mapping to ribosomal RNA-coding regions and reads that did not map uniquely were disregarded. The methods for counting the sequences covering each ORF, for calculating the relative transcript abundance (RTA) 3 for each ORF, and for comparing RTAs between different data sets were performed as described previously (2). The probability (p values) for equal RTA in the respective comparisons was calculated for each ORF either by using the z-test or the 2 test as appropriate (for more details, see Ref.…”

“…PCC 7002 (hereafter Synechococcus 7002), the impact of physicochemical parameters has been extensively studied using global systems biological approaches, including transcriptomics, proteomics, and metabolomics (2)(3)(4)(5)(6). Some changes in culture conditions, such as dark incubation, cause dramatic changes in the transcriptome (2), whereas other conditions, such as limitation for nutrients, cause more specific and limited short term responses (3,4). Large changes in transcript levels for the acsF II -ho2-hemN-desF operon, which encodes key enzymes required for chlorophyll a, phycocyanobilin, heme, and lipid biosynthesis, were observed in response to changes in oxygen (2).…”