Isolation of a novel NAD(P)H-quinone oxidoreductase from the cyanobacterium Synechocystis PCC6803

Transcriptomic Analysis of Degradative Pathways for Azo Dye Acid Blue 113 in Sphingomonas melonis B-2 from the Dye Wastewater Treatment Process

Background: Acid Blue 113 (AB113) is a typical azo dye, and the resulting wastewater is toxic and difficult to remove. Methods: The experimental culture was set up for the biodegradation of the azo dye AB113, and the cell growth and dye decolorization were monitored. Transcriptome sequencing was performed in the presence and absence of AB113 treatment. The key pathways and enzymes involved in AB113 degradation were found through pathway analysis and enrichment software (GO, EggNog and KEGG). Results: S. melonis B-2 achieved more than 80% decolorization within 24 h (50 and 100 mg/L dye). There was a positive relationship between cell growth and the azo dye degradation rate. The expression level of enzymes involved in benzoate and naphthalene degradation pathways (NADH quinone oxidoreductase, N-acetyltransferase and aromatic ring-hydroxylating dioxygenase) increased significantly after the treatment of AB113. Conclusions: Benzoate and naphthalene degradation pathways were the key pathways for AB113 degradation. NADH quinone oxidoreductase, N-acetyltransferase, aromatic ring-hydroxylating dioxygenase and CYP450 were the key enzymes for AB113 degradation. This study provides evidence for the process of AB113 biodegradation at the molecular and biochemical level that will be useful in monitoring the dye wastewater treatment process at the full-scale treatment.

Proteomic profiling of cryopreserved Trichormus variabilis using various cryoprotectants

Algae, which may be unicellular or multicellular, can carry out photosynthesis just like plants as they effectively utilize light energy. They contain various physiologically active substances and are, therefore, widely used commercially to produce healthy food and feed additives, cosmetics, and energy supplements. For useful applications, the cryopreservation technique has been used in various fields. Recently, to develop suitable cryopreservation methods for algal applications, various studies have been performed. However, adequate investigations have not been conducted to understand the mechanism underlying algal cryopreservation at the molecular level. Therefore, this study examined the profile alteration of the proteome using cryopreservation with various cryoprotectants (CPAs). Trichormus variabilis was cultured and then cryopreserved with 10% dimethyl sulfoxide, methanol, and glycerol, after which, proteome profiling was done. Finally, signaling pathway search was performed, and a new signaling pathway was established based on differentially expressed proteins. As a result, the expression levels of 17 proteins were observed. Additionally, it was confirmed that the differentially expressed proteins were related to 16 signaling pathways and that they were capable of interacting with each other. The findings suggest that the differentially expressed proteins may be applied as biomarkers for algal cryopreservation and to understand the mechanism underlying T. variabilis cryopreservation. Moreover, it is anticipated that the results from this study would be useful in selecting suitable CPAs and in upgrading the cryopreservation techniques.

mrpA (all1838), a gene involved in alkali and Na(+) sensitivity, may also have a role in energy metabolism in the cyanobacterium Anabaena sp. strain PCC 7120

Anabaena sp. PCC7120 contains a gene, mrpA (all1838), which forms part of a seven gene-cluster (all1843-all1837) with significant sequence similarity to bacterial operons that putatively code for a multicomponent cation/proton antiporter involved in alkaline pH adaptation and salt resistance. We previously showed that growth and photosynthesis were inhibited in a strain mutated in mrpA, denoted as PHB11, particularly at alkaline pH. Here, we show that respiration was also impaired in the mutant independently of the external pH. In addition, at high pH, less ATP and vegetative cell ferredoxin were present in PHB11, which also showed lower levels of ferredoxin-NADP(+) oxidoreductase (FNR). Ferredoxin and FNR are involved in the generation of reductant NADPH in cyanobacteria. These results suggest an energetic role of mrpA (and perhaps of the whole mrp-gene cluster) in Anabaena sp. PCC 7120 that is further supported by the significant similarity of putative Anabaena Mrp proteins to membrane subunits of complex I.

Reduction of polynitroaromatic compounds: the bacterial nitroreductases

Most nitroaromatic compounds are toxic and mutagenic for living organisms, but some microorganisms have developed oxidative or reductive pathways to degrade or transform these compounds. Reductive pathways are based either on the reduction of the aromatic ring by hydride additions or on the reduction of the nitro groups to hydroxylamino and/or amino derivatives. Bacterial nitroreductases are flavoenzymes that catalyze the NAD(P)H-dependent reduction of the nitro groups on nitroaromatic and nitroheterocyclic compounds. Nitroreductases have raised a great interest due to their potential applications in bioremediation, biocatalysis, and biomedicine, especially in prodrug activation for chemotherapeutic cancer treatments. Different bacterial nitroreductases have been purified and their biochemical and kinetic parameters have been determined. The crystal structure of some nitroreductases have also been solved. However, the physiological role(s) of these enzymes remains unclear. Nitroreductase genes are widely spread within bacterial genomes, but are also found in archaea and some eukaryotic species. Although studies on regulation of nitroreductase gene expression are scarce, it seems that nitroreductase genes may be controlled by the MarRA and SoxRS regulatory systems that are involved in responses to several antibiotics and environmental chemical hazards and to specific oxidative stress conditions. This review covers the microbial distribution, types, biochemical properties, structure and regulation of the bacterial nitroreductases. The possible physiological functions and the biotechnological applications of these enzymes are also discussed.

Synechocystis DrgA protein functioning as nitroreductase and ferric reductase is capable of catalyzing the Fenton reaction

In order to identify an enzyme capable of Fenton reaction in Synechocystis, we purified an enzyme catalyzing one-electron reduction of t-butyl hydroperoxide in the presence of FAD and Fe(III)-EDTA. The enzyme was a 26 kDa protein, and its N-terminal amino acid sequencing revealed it to be DrgA protein previously reported as quinone reductase [Matsuo M, Endo T and Asada K (1998) Plant Cell Physiol39, 751-755]. The DrgA protein exhibited potent quinone reductase activity and, furthermore, we newly found that it contained FMN and highly catalyzed nitroreductase, flavin reductase and ferric reductase activities. This is the first demonstration of nitroreductase activity of DrgA protein previously identified by a drgA mutant phenotype. DrgA protein strongly catalyzed the Fenton reaction in the presence of synthetic chelate compounds, but did so poorly in the presence of natural chelate compounds. Its ferric reductase activity was observed with both natural and synthetic chelate compounds with a better efficiency with the latter. In addition to small molecular-weight chemical chelators, an iron transporter protein, transferrin, and an iron storage protein, ferritin, turned out to be substrates of the DrgA protein, suggesting it might play a role in iron metabolism under physiological conditions and possibly catalyze the Fenton reaction under hyper-reductive conditions in this microorganism.

Cyclic electron transport around photosystem I: genetic approaches

The light reactions in photosynthesis convert light energy into chemical energy in the form of ATP and drive the production of NADPH from NADP+. The reactions involve two types of electron flow in the chloroplast. While linear electron transport generates both ATP and NADPH, photosystem I cyclic electron transport is exclusively involved in ATP synthesis. The physiological significance of photosystem I cyclic electron transport has been underestimated, and our knowledge of the machineries involved remains very limited. However, recent genetic approaches using Arabidopsis thaliana have clarified the essential functions of this electron flow in both photoprotection and photosynthesis. Based on several lines of evidence presented here, it is necessary to reconsider the fundamental mechanisms of chloroplast energetics.

New subunits NDH-M, -N, and -O, encoded by nuclear genes, are essential for plastid Ndh complex functioning in higher plants

In higher plants, the Ndh complex reduces plastoquinones and is involved in cyclic electron flow around photosystem I, supplying extra-ATP for photosynthesis, particularly under environmental stress conditions. Based on plastid genome sequences, the Ndh complex would contain 11 subunits (NDH-A to -K), but homologies with bacterial complex indicate the probable existence of additional subunits. To identify missing subunits, tobacco (Nicotiana tabacum) NDH-H was His tagged at its N terminus using plastid transformation. A functional Ndh subcomplex was purified by Ni(2+) affinity chromatography and its subunit composition analyzed by mass spectrometry. Five plastid encoded subunits (NDH-A, -H, -I, -J, and -K) were identified as well as three new subunits (NDH-M, -N, and -O) homologous to cyanobacterial and higher plant proteins. Arabidopsis thaliana mutants missing one of these new subunits lack a functional Ndh complex, and NDH-M and NDH-N are not detected in a tobacco transformant lacking the Ndh complex. We discuss the involvement of these three nuclear-encoded subunits in the functional integrity of the plastidial complex.

Type 2 NADH dehydrogenases in the cyanobacterium Synechocystis sp. strain PCC 6803 are involved in regulation rather than respiration

Analysis of the genome of Synechocystis sp. strain PCC 6803 reveals three open reading frames (slr0851, slr1743, and sll1484) that may code for type 2 NAD(P)H dehydrogenases (NDH-2). The sequence similarity between the translated open reading frames and NDH-2s from other organisms is low, generally not exceeding 30% identity. However, NAD(P)H and flavin adenine dinucleotide binding motifs are conserved in all three putative NDH-2s in Synechocystis sp. strain PCC 6803. The three open reading frames were cloned, and deletion constructs were made for each. An expression construct containing one of the three open reading frames, slr1743, was able to functionally complement an Escherichia coli mutant lacking both NDH-1s and NDH-2s. Therefore, slr0851, slr1743, and sll1484 have been designated ndbA, ndbB, and ndbC, respectively. Strains that lacked one or more of the ndb genes were created in wild-type and photosystem (PS) I-less backgrounds. Deletion of ndb genes led to small changes in photoautotrophic growth rates and respiratory activities. Electron transfer rates into the plastoquinone pool in thylakoids in darkness were consistent with the presence of a small amount of NDH-2 activity in thylakoids. No difference was observed between wild-type and the Ndb-less strains in the banding patterns seen on native gels when stained for either NADH or NADPH dehydrogenase activity, indicating that the Ndb proteins do not accumulate to high levels. A striking phenotype of the PS I-less background strains lacking one or more of the NDH-2s is that they were able to grow at high light intensities that were lethal to the control strain but they retained normal PS II activity. We suggest that the Ndb proteins in Synechocystis sp. strain PCC 6803 are redox sensors and that they play a regulatory role responding to the redox state of the plastoquinone pool.