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Simple Summary: Trehalose is an easily and economically obtainable non-reducing disaccharide, readily taken up by living organisms upon external application. Arthrospira platensis grew photoautotrophically under nitrogen-deficient conditions supplied with the appropriate trehalose, promoting glycogen and PHB production. This is supported by a notable increase in the upregulation of glgA and phaC expression, along with the induction of enzyme activity, including glycogen synthase encoded by glgA and PHA synthase encoded by phaC. The present study offers new insights into the contribution of exogenous trehalose in the regulation of glycogen and PHB production in A. platensis. Glycogen and poly-3-hydroxybutyrate (PHB) are excellent biopolymer products from cyanobacteria. In this study, we demonstrate that nitrogen metabolism is positively influenced by the exogenous application of trehalose (Tre) in Arthrospira platensis under nitrogen-deprived (−N) conditions. Cells were cultivated photoautotrophically for 5 days under −N conditions, with or without the addition of exogenous Tre. The results revealed that biomass and chlorophyll-a content of A. platensis experienced enhancement with the addition of 0.003 M and 0.03 M Tre in the −N medium after one day, indicating relief from growth inhibition caused by nitrogen deprivation. The highest glycogen content (54.09 ± 1.6% (w/w) DW) was observed in cells grown for 2 days under the −N + 0.003 M Tre condition (p < 0.05), while the highest PHB content (15.2 ± 0.2% (w/w) DW) was observed in cells grown for 3 days under the −N + 0.03 M Tre condition (p < 0.05). The RT-PCR analysis showed a significant increase in glgA and phaC transcript levels, representing approximately 1.2- and 1.3-fold increases, respectively, in A. platensis grown under −N + 0.003 M Tre and −N + 0.03 M Tre conditions. This was accompanied by the induction of enzyme activities, including glycogen synthase and PHA synthase with maximal values of 89.15 and 0.68 µmol min−1 mg−1 protein, respectively. The chemical structure identification of glycogen and PHB from A. platensis was confirmed by FTIR and NMR analysis. This research represents the first study examining the performance of trehalose in promoting glycogen and PHB production in cyanobacteria under nitrogen-deprived conditions. [ABSTRACT FROM AUTHOR]

Simple Summary: The cyanobacterium Arthrospira platensis contains PHA synthase Class III (PhaCAp), which can produce short chain length (SCL) PHB under nitrogen-depleted conditions. In this study, we cloned a gene encoding PhaC from A. platensis into Escherichia cloni ®10G cells to produce rPhaCAp protein. The Vmax, Km, and kcat values for β-3-hydroxybutyryl coenzyme A (3HB-CoA) of the purified rPhaCAp were investigated. Size-exclusion chromatography revealed that rPhaCAp exists as an active dimer. The overall fold and catalytic triad residues were predicted using the 3D structural model for rPhaCAp. These results are discussed with respect to the dimerization mechanism of PhaCAp, which has not yet been clarified. Polyhydroxybutyrate (PHB) is a biocompatible and biodegradable polymer that has the potential to replace fossil-derived polymers. The enzymes involved in the biosynthesis of PHB are β-ketothiolase (PhaA), acetoacetyl-CoA reductase (PhaB), and PHA synthase (PhaC). PhaC in Arthrospira platensis is the key enzyme for PHB production. In this study, the recombinant E. cloni ®10G cells harboring A. platensis phaC (rPhaCAp) was constructed. The overexpressed and purified rPhaCAp with a predicted molecular mass of 69 kDa exhibited Vmax, Km, and kcat values of 24.5 ± 2 μmol/min/mg, 31.3 ± 2 µM and 412.7 ± 2 1/s, respectively. The catalytically active rPhaCAp was a homodimer. The three-dimensional structural model for the asymmetric PhaCAp homodimer was constructed based on Chromobacterium sp. USM2 PhaC (PhaCCs). The obtained model of PhaCAp revealed that the overall fold of one monomer was in the closed, catalytically inactive conformation whereas the other monomer was in the catalytically active, open conformation. In the active conformation, the catalytic triad residues (Cys151-Asp310-His339) were involved in the binding of substrate 3HB-CoA and the CAP domain of PhaCAp involved in the dimerization. [ABSTRACT FROM AUTHOR]

Hydrogen produced from microalgae is attracting the attention of scientists as a potential new 'Bio-Circular-Green' energy source. We screened a selection of naturally occurring algal strains for H2 yield as a basis for high yield development. The best strain was a new strain of biohydrogen-producing green algae from a fresh water source at King Mongkut's Institute of Technology Ladkrabang, Thailand. Using morphological and 18S rDNA sequencing analyses, this alga was identified and classified as Chlorella sp. KLSc61. When adapted cells in TAP-K medium (with starting pH at 9.0) containing 25 mM ethanol, with 54 μmol photons m−2 s−1 light, and incubated at 35 °C, Chlorella sp. KLSc61 showed a maximum H2 yield of 9,804 ± 469.5 μmol H2 mg−1 Chl at day 7. Under these conditions, the cells produced ~ 12.2 times more H2 gas than without optimization (753.0 μmol H2 mg−1Chl). Our optimized system also produced H2 at a rate 11–570 times greater than previously reported microalgae. Thus Chlorella sp. KLSc61 could be a viable strain for biohydrogen production as a clean future energy source. [ABSTRACT FROM AUTHOR]

Abstract Background DnaJ proteins participate in many metabolic pathways through dynamic interactions with various components of these processes. The role of three small chloroplast-targeted DnaJ proteins, AtJ8 (At1 g80920), AtJ11 (At4 g36040) and AtJ20 (At4 g13830), was investigated here using knock-out mutants of Arabidopsis thaliana. Photochemical efficiency, capacity of CO2 assimilation, stabilization of Photosystem (PS) II dimers and supercomplexes under high light illumination, energy distribution between PSI and PSII and phosphorylation of PSII-LHCII proteins, global gene expression profiles and oxidative stress responses of these DnaJ mutants were analyzed. Results Knockout of one of these proteins caused a series of events including a decrease in photosynthetic efficiency, destabilization of PSII complexes and loss of control for balancing the redox reactions in chloroplasts. Data obtained with DNA microarray analysis demonstrated that the lack of one of these DnaJ proteins triggers a global stress response and therefore confers the plants greater tolerance to oxidative stress induced by high light or methyl viologen treatments. Expression of a set of genes encoding enzymes that detoxify reactive oxygen species (ROS) as well as a number of stress-related transcription factors behaved in the mutants at growth light similarly to that when wild-type (WT) plants were transferred to high light. Also a set of genes related to redox regulation were upregulated in the mutants. On the other hand, although the three DnaJ proteins reside in chloroplasts, the expression of most genes encoding thylakoid membrane proteins was not changed in the mutants. Conclusion It is proposed that the tolerance of the DnaJ protein knockout plants to oxidative stress occurs at the expense of the flexibility of photosynthetic reactions. Despite the fact that the effects of the individual protein knockout on the response of plants to high light treatment are quite similar, it is conceivable that both specific- and cross-talk functions exist between the three small chloroplast-targeted DnaJ proteins, AtJ8, AtJ11 and AtJ20.

Background: DnaJ proteins participate in many metabolic pathways through dynamic interactions with various components of these processes. The role of three small chloroplast-targeted DnaJ proteins, AtJ8 (At1 g80920), AtJ11 (At4 g36040) and AtJ20 (At4 g13830), was investigated here using knock-out mutants of Arabidopsis thaliana. Photochemical efficiency, capacity of CO2 assimilation, stabilization of Photosystem (PS) II dimers and supercomplexes under high light illumination, energy distribution between PSI and PSII and phosphorylation of PSII-LHCII proteins, global gene expression profiles and oxidative stress responses of these DnaJ mutants were analyzed. Results: Knockout of one of these proteins caused a series of events including a decrease in photosynthetic efficiency, destabilization of PSII complexes and loss of control for balancing the redox reactions in chloroplasts. Data obtained with DNA microarray analysis demonstrated that the lack of one of these DnaJ proteins triggers a global stress response and therefore confers the plants greater tolerance to oxidative stress induced by high light or methyl viologen treatments. Expression of a set of genes encoding enzymes that detoxify reactive oxygen species (ROS) as well as a number of stress-related transcription factors behaved in the mutants at growth light similarly to that when wild-type (WT) plants were transferred to high light. Also a set of genes related to redox regulation were upregulated in the mutants. On the other hand, although the three DnaJ proteins reside in chloroplasts, the expression of most genes encoding thylakoid membrane proteins was not changed in the mutants. Conclusion: It is proposed that the tolerance of the DnaJ protein knockout plants to oxidative stress occurs at the expense of the flexibility of photosynthetic reactions. Despite the fact that the effects of the individual protein knockout on the response of plants to high light treatment are quite similar, it is conceivable that both specificand cross-talk functions exist between the three small chloroplast-targeted DnaJ proteins, AtJ8, AtJ11 and AtJ20. [ABSTRACT FROM AUTHOR]

Aphanothece cells could take up Na+ and this uptake was strongly inhibited by the protonophore, carbonyl cyanide m-chlorophenylhydrazone (CCCP). Cells preloaded with Na+ exhibited Na+ extrusion ability upon energizing with glucose. Na+ was also taken up by the plasma membranes supplied with ATP and the uptake was abolished by gramicidin D, monensin or Na+-ionophore. Orthovanadate and CCCP strongly inhibited Na+ uptake, whereas N, N′-dicyclohexylcarbodiimide (DCCD) slightly inhibited the uptake. Plasma membranes could hydrolyse ATP in the presence of Na+ but not with K+, Ca2+ and Li+. The Km values for ATP and Na+ were 1.66±0.12 and 25.0±1.8 mM, respectively, whereas the Vmax value was 0.66±0.05 μmol min−1 mg−1. Mg2+ was required for ATPase activity whose optimal pH was 7.5. The ATPase was insensitive to N-ethylmaleimide, nitrate, thiocyanate, azide and ouabain, but was substantially inhibited by orthovanadate and DCCD. Amiloride, a Na+/H+ antiporter inhibitor, and CCCP showed little or no effect. Gramicidin D and monensin stimulated ATPase activity. All these results suggest the existence of a P-type Na+-stimulated ATPase in Aphanothece halophytica. Plasma membranes from cells grown under salt stress condition showed higher ATPase activity than those from cells grown under nonstress condition. [ABSTRACT FROM AUTHOR]

The transport of putrescine into a moderately salt tolerant cyanobacterium Synechocystis sp. PCC 6803 was characterized by measuring the uptake of radioactively-labeled putrescine. Putrescine transport showed saturation kinetics with an apparent K(m) of 92 +/- 10 microM and V(max) of 0.33 +/- 0.05 nmol/min/mg protein. The transport of putrescine was pH-dependent with highest activity at pH 7.0. Strong inhibition of putrescine transport was caused by spermine and spermidine whereas only slight inhibition was observed by the addition of various amino acids. These results suggest that the transport system in Synechocystis sp. PCC 6803 is highly specific for polyamines. Putrescine transport is energy-dependent as evidenced by the inhibition by various metabolic inhibitors and ionophores. Slow growth was observed in cells grown under salt stress. Addition of low concentration of putrescine could restore growth almost to the level observed in the absence of salt stress. Upshift of the external osmolality generated by either NaCl or sorbitol caused an increased putrescine transport with an optimum 2-fold increase at 20 mosmol/kg. The stimulation of putrescine transport mediated by osmotic upshift was abolished in chloramphenicol-treated cells, suggesting possible involvement of an inducible transport system.