Strains Of Synechococcus Sp Research Articles

Nitrogen starvation–induced oxidative stress relieves PII-mediated inhibition of acetyl-CoA carboxylase (ACCase) activity and signals enhanced lipid synthesis in Synechococcus PCC 7942

The present study shows the existence of PII-acetyl-CoA carboxylase interaction in the cyanobacterium Synechococcus sp. PCC 7942 and the possible adverse impact of nitrogen starvation on this interaction. The in silico and in vitro analysis of PII-acetyl-CoA carboxylase interaction revealed that the biotin carboxyl carrier protein subunit of acetyl-CoA carboxylase enzyme actually interacts with the T-loop of PII protein. However, exposure of the cyanobacterium to nitrogen-starved condition showed a higher expression and activity of acetyl-CoA carboxylase at the intracellular level which denoted the impairment of PII-acetyl-CoA carboxylase interaction. A similar stimulatory effect of nitrogen starvation has also been noticed in the PII mutant of Synechococcus PCC 7942. Further, the physiological study reflected that nitrogen starvation–caused reactive oxygen species generation in the wild-type and PII mutant strains and lipid was increased in both strains of Synechococcus sp. PCC 7942. Proteomic analysis showed the upregulation of glycogen synthase, biotin carboxylase, and antioxidative enzymes and the deregulation of proteins involved in photosynthesis, energy metabolism, and protein synthesis. Interestingly, enhanced accumulation of transcripts of few tricarboxylic acid cycle genes was also noticed in the wild type. Although oxidative stress and lipid production were enhanced in both the test strains under nitrogen starvation, the impacts were more prominent in the mutant strain. Our results suggest that the nitrogen starvation–induced oxidative stress possibly relieved the PII-mediated inhibition of acetyl-CoA carboxylase and led to increased lipid synthesis in Synechococcus PCC 7942.

Microcystins production and antibacterial activity of cyanobacterial strains of Synechocystis, Synechococcus and Romeria isolated from water and coral reef organisms of Brazilian coast

Cyanobacteria are widely distributed in terrestrial, freshwater and marine environments, and over the past decades have been recognized as a powerful source of bioactive compounds. In this study, some cyanobacterial strains were isolated from samples of seawater, brackish water and tissue of reef benthic invertebrates (zoanthid Protopalythoa variabilis, the sponges Cynachrella sp. and Haliclona sp., the coral Siderastrea stellata, and ascidians), collected at the states of Paraiba and Rio Grande do Norte (Northeast of Brazil), during the period between July 2010 and February 2014. After standard isolation methods, the cultivation of the strains was carried out in acclimatized culture chamber (25 °C) under constant aeration, for 15 days at 12-hour photoperiod, using Conway and BG11 media made with filtered seawater. After ethanolic and methanolic extracts, the strains were analysed for the microcystin production by the ELISA technique and for the antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa by the agar well diffusion method. The detection of the mcy B gene, one of the genes related to the microcystin synthesis, was done by the Polymerase Chain Reaction (PCR) technique. The majority of the eighteen cyanobacterial strains belonged to Synechococcaceae Family. The genera of Synechocystis, Synechococcus and Romeria were represented by ten, six and two strains, respectively. The production of microcystins was observed in five strains belonging to the genus Synechocystis . The presence of mcy B gene was detected in 12 strains of cyanobacteria: Synechocystis (three strains), Synechococcus (six strains) and Romeria (two strains). Only one strain ( Synechocystis aquatilis ) showed both the microcystin production and the mcy B gene presence. The antibacterial activity was observed for one strain of Romeria gracilis , one strain of Synechocystis aquatilis and two strains of Synechococcus sp. The ethanolic extracts of R. gracilis strain and two Synechococcus spp. strains inhibited the growth of P. aeruginosa . Among methanolic extracts of cyanobacteria, only one strain of S. aquatilis showed activity against S. aureus, and one R. gracilis strain against P. aeruginosa . Some cyanobacterial strains studied were positive for the microcystin production and antibacterial activity against pathogenic bacteria S. aureus and P. aeuruginosa , and may be further explored for additional biotechnological applications.

Microcystins production and antibacterial activity of cyanobacterial strains of Synechocystis, Synechococcus and Romeria isolated from water and coral reef organisms of Brazilian coast

Cyanobacteria are widely distributed in terrestrial, freshwater and marine environments, and over the past decades have been recognized as a powerful source of bioactive compounds. In this study, some cyanobacterial strains were isolated from samples of seawater, brackish water and tissue of reef benthic invertebrates (zoanthid Protopalythoa variabilis, the sponges Cynachrella sp. and Haliclona sp., the coral Siderastrea stellata, and ascidians), collected at the states of Paraíba and Rio Grande do Norte (Northeast of Brazil), during the period between July 2010 and February 2014. After standard isolation methods, the cultivation of the strains was carried out in acclimatized culture chamber (25 °C) under constant aeration, for 15 days at 12-hour photoperiod, using Conway and BG11 media made with filtered seawater. After ethanolic and methanolic extracts, the strains were analysed for the microcystin production by the ELISA technique and for the antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa by the agar well diffusion method. The detection of the mcyB gene, one of the genes related to the microcystin synthesis, was done by the Polymerase Chain Reaction (PCR) technique. The majority of the eighteen cyanobacterial strains belonged to Synechococcaceae Family. The genera of Synechocystis, Synechococcus and Romeria were represented by ten, six and two strains, respectively. The production of microcystins was observed in five strains belonging to the genus Synechocystis. The presence of mcyB gene was detected in 12 strains of cyanobacteria: Synechocystis (three strains), Synechococcus (six strains) and Romeria (two strains). Only one strain (Synechocystis aquatilis) showed both the microcystin production and the mcyB gene presence. The antibacterial activity was observed for one strain of Romeria gracilis, one strain of Synechocystis aquatilis and two strains of Synechococcus sp. The ethanolic extracts of R. gracilis strain and two Synechococcus spp. strains inhibited the growth of P. aeruginosa. Among methanolic extracts of cyanobacteria, only one strain of S. aquatilis showed activity against S. aureus, and one R. gracilis strain against P. aeruginosa. Some cyanobacterial strains studied were positive for the microcystin production and antibacterial activity against pathogenic bacteria S. aureus and P. aeuruginosa, and may be further explored for additional biotechnological applications.

Regulatory Roles for IscA and SufA in Iron Homeostasis and Redox Stress Responses in the Cyanobacterium Synechococcus sp. Strain PCC 7002

SufA, IscA, and Nfu have been proposed to function as scaffolds in the assembly of Fe/S clusters in bacteria. To investigate the roles of these proteins further, single and double null-mutant strains of Synechococcus sp. strain PCC 7002 were constructed by insertional inactivation of genes homologous to sufA, iscA, and nfu. Demonstrating the nonessential nature of their products, the sufA, iscA, and sufA iscA mutants grew photoautotrophically with doubling times that were similar to the wild type under standard growth conditions. In contrast, attempts to inactivate the nfu gene only resulted in stable merodiploids. These results imply that Nfu, but not SufA or IscA, is the essential Fe/S scaffold protein in cyanobacteria. When cells were grown under iron-limiting conditions, the iscA and sufA mutant strains exhibited less chlorosis than the wild type. Under iron-sufficient growth conditions, isiA transcript levels, a marker for iron limitation in cyanobacteria, as well as transcript levels of genes in both the suf and isc regulons were significantly higher in the iscA mutant than in the wild type. Under photosynthesis-induced redox stress conditions, the transcript levels of the suf genes are notably higher in the sufA and the sufA iscA mutants than in the wild type. The growth phenotypes and mRNA abundance patterns of the mutant strains contradict the proposed scaffold function for the SufA and IscA proteins in generalized Fe/S cluster assembly and instead suggest that they play regulatory roles in iron homeostasis and the sensing of redox stress in cyanobacteria.

Nitrogen-regulated hypermutator strain of Synechococcus sp. for use in in vivo artificial evolution.

Artificially evolved variants of proteins with roles in photosynthesis may be selected most conveniently by using a photosynthetic organism, such as a cyanobacterium, whose growth depends on the function of the target protein. However, the limited transformation efficiency of even the most transformable cyanobacteria wastes much of the diversity of mutant libraries of genes produced in vitro, impairing the coverage of sequence space. This highlights the advantages of an in vivo approach for generating diversity in the selection organism itself. We constructed two different hypermutator strains of Synechococcus sp. strain PCC 7942 by insertionally inactivating or nutritionally repressing the DNA mismatch repair gene, mutS. Inactivation of mutS greatly increases the mutation rate of the cyanobacterium's genes, leading to an up-to-300-fold increase in the frequency of resistance to the antibiotics rifampin and spectinomycin. In order to control the rate of mutation and to limit cellular damage resulting from prolonged hypermutation, we placed the uninterrupted mutS gene in the cyanobacterial chromosome under the transcriptional control of the cyanobacterial nirA promoter, which is repressed in the presence of NH(4)(+) as an N source and derepressed in its absence. By removing or adding this substrate, hypermutation was activated or repressed as required. As expected, hypermutation caused by repression in PnirA-mutS transformants led to an accumulation of spectinomycin resistance mutations during growth.

Regulation of the distribution of chlorophyll and phycobilin-absorbed excitation energy in cyanobacteria. A structure-based model for the light state transition.

The light state transition regulates the distribution of absorbed excitation energy between the two photosystems (PSs) of photosynthesis under varying environmental conditions and/or metabolic demands. In cyanobacteria, there is evidence for the redistribution of energy absorbed by both chlorophyll (Chl) and by phycobilin pigments, and proposed mechanisms differ in the relative involvement of the two pigment types. We assayed changes in the distribution of excitation energy with 77K fluorescence emission spectroscopy determined for excitation of Chl and phycobilin pigments, in both wild-type and state transition-impaired mutant strains of Synechococcus sp. PCC 7002 and Synechocystis sp. PCC 6803. Action spectra for the redistribution of both Chl and phycobilin pigments were very similar in both wild-type cyanobacteria. Both state transition-impaired mutants showed no redistribution of phycobilin-absorbed excitation energy, but retained changes in Chl-absorbed excitation. Action spectra for the Chl-absorbed changes in excitation in the two mutants were similar to each other and to those observed in the two wild types. Our data show that the redistribution of excitation energy absorbed by Chl is independent of the redistribution of excitation energy absorbed by phycobilin pigments and that both changes are triggered by the same environmental light conditions. We present a model for the state transition in cyanobacteria based on the x-ray structures of PSII, PSI, and allophycocyanin consistent with these results.