Responses Of Synechocystis Sp Research Articles

Response of Synechocystis sp. PCC 6803 to UV radiations by alteration of polyamines associated with thylakoid membrane proteins.

The responses of Synechocystis sp. PCC 6803 exposed to UVA, UVB and UVC for at least 3h were investigated with the emphasis on the changes of polyamines (PAs) levels in whole cells, thylakoid membrane fraction, and thylakoid membrane-associated proteins fraction. All UV radiations caused a slight decrease on cell growth but a drastic reduction of photosynthetic efficiency of Synechocystis cells. UV radiations, especially UVB and UVC, severely decreased the levels of PAs associated with thylakoid membrane proteins. The decreased PAs levels as affected by UV radiation correlated well with the decrease of photosynthetic efficiency, suggesting the role of PAs for the maintenance of photosynthetic activity of Synechocystis. PAs, especially spermidine (Spd) and putrescine (Put), were found abundantly in the thylakoid membrane fraction, and these PAs were associated mainly with the PSI trimer complex. Importantly, the exposure of Synechocystis cells to all UV radiations for 3h resulted in the increase of Spd associated with the PSII monomer and dimer complex, suggesting its protective role against UV radiations despite the overall decrease of PAs.

Coping with iron limitation: a metabolomic study of Synechocystis sp. PCC 6803

Iron (Fe) is a key element for all living systems, especially for photosynthetic organisms because of its important role in the photosynthetic electron transport chain. Fe limitation in cyanobacteria leads to several physiological and morphological changes. However, the overall metabolic responses to Fe limitation are still poorly understood. In this study, we integrated elemental, stoichiometric, macromolecular, and metabolomic data to shed light on the responses of Synechocystis sp. PCC 6803, a non-N2-fixing freshwater cyanobacterium, to Fe limitation. Compared to Synechocystis growing at nutrient replete conditions, Fe-limited cultures had lower growth rates and amounts of chlorophyll a, RNA, RNA:DNA, C, N, and P, and higher ratios of protein:RNA, C:N, C:P, and N:P, in accordance with the growth rate hypothesis which predicts faster growing organisms will have decreased biomass RNA contents and C:P and N:P ratios. Fe-limited Synechocystis had lower amounts Fe, Mn, and Mo, and higher amount of Cu. Several changes in amino acids of cultures growing under Fe limitation suggest nitrogen limitation. In addition, we found substantial increases in stress-related metabolites in Fe-limited cyanobacteria such antioxidants. This study represents an advance in understanding the stoichiometric, macromolecular, and metabolic strategies that cyanobacteria use to cope with Fe limitation. This information, moreover, may further understanding of changes in cyanobacterial functions under scenarios of Fe limitation in aquatic ecosystems.

6S RNA plays a role in recovery from nitrogen depletion in Synechocystis sp. PCC 6803

BackgroundThe 6S RNA is a global transcriptional riboregulator, which is exceptionally widespread among most bacterial phyla. While its role is well-characterized in some heterotrophic bacteria, we subjected a cyanobacterial homolog to functional analysis, thereby extending the scope of 6S RNA action to the special challenges of photoautotrophic lifestyles.ResultsPhysiological characterization of a 6S RNA deletion strain (ΔssaA) demonstrates a delay in the recovery from nitrogen starvation. Significantly decelerated phycobilisome reassembly and glycogen degradation are accompanied with reduced photosynthetic activity compared to the wild type. Transcriptome profiling further revealed that predominantly genes encoding photosystem components, ATP synthase, phycobilisomes and ribosomal proteins were negatively affected in ΔssaA. In vivo pull-down studies of the RNA polymerase complex indicated that the presence of 6S RNA promotes the recruitment of the cyanobacterial housekeeping σ factor SigA, concurrently supporting dissociation of group 2 σ factors during recovery from nitrogen starvation.ConclusionsThe combination of genetic, physiological and biochemical studies reveals the homologue of 6S RNA as an integral part of the cellular response of Synechocystis sp. PCC 6803 to changing nitrogen availability. According to these results, 6S RNA supports a rapid acclimation to changing nitrogen supply by accelerating the switch from group 2 σ factors SigB, SigC and SigE to SigA-dependent transcription. We therefore introduce the cyanobacterial 6S RNA as a novel candidate regulator of RNA polymerase sigma factor recruitment in Synechocystis sp. PCC 6803. Further studies on mechanistic features of the postulated interaction should shed additional light on the complexity of transcriptional regulation in cyanobacteria.

Responses of Synechocystis sp. PCC 6803 to heterologous biosynthetic pathways

BackgroundThere are an increasing number of studies regarding genetic manipulation of cyanobacteria to produce commercially interesting compounds. The majority of these works study the expression and optimization of a selected heterologous pathway, largely ignoring the wholeness and complexity of cellular metabolism. Regulation and response mechanisms are largely unknown, and even the metabolic pathways themselves are not fully elucidated. This poses a clear limitation in exploiting the rich biosynthetic potential of cyanobacteria.ResultsIn this work, we focused on the production of two different compounds, the cyanogenic glucoside dhurrin and the diterpenoid 13R-manoyl oxide in Synechocystis PCC 6803. We used genome-scale metabolic modelling to study fluxes in individual reactions and pathways, and we determined the concentrations of key metabolites, such as amino acids, carotenoids, and chlorophylls. This allowed us to identify metabolic crosstalk between the native and the introduced metabolic pathways. Most results and simulations highlight the metabolic robustness of cyanobacteria, suggesting that the host organism tends to keep metabolic fluxes and metabolite concentrations steady, counteracting the effects of the heterologous pathway. However, the amino acid concentrations of the dhurrin-producing strain show an unexpected profile, where the perturbation levels were high in seemingly unrelated metabolites.ConclusionsThere is a wealth of information that can be derived by combining targeted metabolite identification and computer modelling as a frame of understanding. Here we present an example of how strain engineering approaches can be coupled to ‘traditional’ metabolic engineering with systems biology, resulting in novel and more efficient manipulation strategies.

Responses of Synechocystis sp. PCC 6803 to total dissolved solids in long-term continuous operation of a photobioreactor

This study evaluated how Synechocystis sp. PCC 6803 responds to high total dissolved solids (TDS) associated with eliminating nutrient limitation during long-term operation of a photobioreactor. The unique feature is that the TDS were not dominated by Na+ and Cl−, as in seawater, but by HCO3− and NO3− from nutrient delivery. The TDS-stress threshold was about 10g/L. Whereas inorganic N and P limitations slowed the rate of inorganic C (Ci) uptake in the light, TDS stress was manifested most strongly as a substantial increase of endogenous respiration rate at night. Relief from TDS stress was incomplete when lowered pH led to a HCO3− increase (560mgC/L as a threshold). Impaired photosynthesis led to a cascade of reduced Ci-uptake, pH decrease, HCO3− accumulation, and HCO3−-associated stress. Thus, long-term photobioreactor operation requires balancing the delivery rates of CO2, N, P, and other TDS components to avoid general and Ci-associated TDS stresses.

Physiological Responses of Synechocystis sp. PCC 6803 under Clinorotation

Photosystem efficiency and the characteristic on oxidative stress were examined to elucidate the metabolic responses of Synechocystis sp. PCC 6803 to short-term clinorotation. Results compiled when using clinostat to simulate microgravity for 60 h, showed that clinorotation clearly prohibited the photochemical quantum yield, but promoted the synthesis of chlorophyll and total protein. This may be a compensatory mechanism for the algal cell to maintain its normal metabolism. An increased malondialdehyde (MDA) content of algal cell upon clinorotation, together with an enhanced catalase (CAT) activity was observed during the whole period of clinorotation. One conclusion is that short-term clinorotation acts as a kind of stress, and that these physiological responses may be a special way for an algal cell to adapt itself to a different environment other than earth gravity.

Responses of Synechocystis sp. PCC 6803 (cyanobacterium) photosystem II to pyrene stress

In order to explore the mechanism of acute toxicity for pyrene to cyanobacterial organisms, the responses of Synechocystis sp. PCC 6803 photosystem II (PS II) under pyrene stress were studied. The results showed there was no significant difference about the oxygen evolution under 0.125 mg/L pyrene stress when compared with control, but it was significantly lower than control at 0.625 mg/L pyrene. Polyphasic chlorophyll -a fluorescence transients in cells of Synechocystis sp. PCC 6803 exhibited a typical increase including O, J, I, and P phases. Fluorescence yield at phases J, I and P declined slightly at 0.125 and 0.625 mg/L pyrene, and significantly lower than control at 3.125 mg/L. According to the parameters deviated from JIP-test, no modification was induced by pyrene both at the donor side and at the acceptor side of PS II, and the reaction centre of PS II is the primary damaging target. Based on the expressing of four key genes ( psbA, psbB, psbC and psbO) of PS II, only psbA showed significant difference at 3.125 mg/L pyrene when compared with control.

A systems biology approach to investigate the response of Synechocystis sp. PCC6803 to a high salt environment

BackgroundSalt overloading during agricultural processes is causing a decrease in crop productivity due to saline sensitivity. Salt tolerant cyanobacteria share many cellular characteristics with higher plants and therefore make ideal model systems for studying salinity stress. Here, the response of fully adapted Synechocystis sp. PCC6803 cells to the addition of 6% w/v NaCl was investigated using proteomics combined with targeted analysis of transcripts.ResultsIsobaric mass tagging of peptides led to accurate relative quantitation and identification of 378 proteins, and approximately 40% of these were differentially expressed after incubation in BG-11 media supplemented with 6% salt for 9 days. Protein abundance changes were related to essential cellular functional alterations. Differentially expressed proteins involved in metabolic responses were also analysed using the probabilitistic tool Mixed Model on Graphs (MMG), where the role of energy conversion through glycolysis and reducing power through pentose phosphate pathway were highlighted. Temporal RT-qPCR experiments were also run to investigate protein expression changes at the transcript level, for 14 non-metabolic proteins. In 9 out of 14 cases the mRNA changes were in accordance with the proteins.ConclusionSynechocystis sp. PCC6803 has the ability to regulate essential metabolic processes to enable survival in high salt environments. This adaptation strategy is assisted by further regulation of proteins involved in non-metabolic cellular processes, supported by transcriptional and post-transcriptional control. This study demonstrates the effectiveness of using a systems biology approach in answering environmental, and in particular, salt adaptation questions in Synechocystis sp. PCC6803