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Incharoensakdi, Aran,Laloknam, Surasak Korean Society for Biochemistry and Molecular Biol 2005 Journal of biochemistry and molecular biology Vol.38 No.4
The energetics of nitrate uptake by intact cells of the halotolerant cyanobacterium Aphanothece halophytica were investigated. Nitrate uptake was inhibited by various protonophores suggesting the coupling of nitrate uptake to the proton motive force. An artificially-generated pH gradient across the membrane (${\Delta}pH$) caused an increase of nitrate uptake. In contrast, the suppression of ${\Delta}pH$ resulted in a decrease of nitrate uptake. The increase of external pH also resulted in an enhancement of nitrate uptake. The generation of the electrical potential across the membrane ($\Delta\psi$) resulted in no elevation of the rate of nitrate uptake. On the other hand, the valinomycin-mediated dissipation of $\Delta\psi$ caused no depression of the rate of nitrate uptake. Thus, it is unlikely that $\Delta\psi$ participated in the energization of the uptake of nitrate. However, $Na^+$-gradient across the membrane was suggested to play a role in nitrate uptake since monensin which collapses $Na^+$-gradient strongly inhibited nitrate uptake. Exogenously added glucose and lactate stimulated nitrate uptake in the starved cells. N, N'-dicyclohexylcarbodiimide, an inhibitor of ATPase, could also inhibit nitrate uptake suggesting that ATP hydrolysis was required for nitrate uptake. All these results indicate that nitrate uptake in A. halophytica is ATP-dependent, driven by ${\Delta}pH$ and $Na^+$-gradient.
Metabolic Engineering and Synthetic Biology of Cyanobacteria for Carbon Capture and Utilization
Napisa Pattharaprachayakul,최종일,Aran Incharoensakdi,우한민 한국생물공학회 2020 Biotechnology and Bioprocess Engineering Vol.25 No.6
Cyanobacteria are photosynthetic bacteria that can directly convert CO2 into several bio-products for industrial use, such as alcohols and diols, terpenes, acids, and sugars. However, some of these compounds are either produced in low amounts or are absent in cyanobacteria, and thus strain development is required to achieve optimal production of these bio-products for industrial applications. Metabolic engineering has been applied to modify cyanobacteria for enhanced production of value-added compounds. In this review, we have elucidated metabolic engineering of various pathways with the yield and productivity of the desired products. We have also described recent overall strategies in advanced metabolic engineering.
Putrescine Transport in a Cyanobacterium Synechocystis sp. PCC 6803
Raksajit, Wuttinun,Maenpaa, Pirkko,Incharoensakdi, Aran Korean Society for Biochemistry and Molecular Biol 2006 Journal of biochemistry and molecular biology Vol.39 No.4
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 $92{\pm}10\;{\mu}M$ and $V_{max}$ of $0.33{\pm}0.05\;nmol/min/mg$ 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.
Pattharaprachayakul, Napisa,Lee, Hyun Jeong,Incharoensakdi, Aran,Woo, Han Min American Chemical Society 2019 Journal of agricultural and food chemistry Vol.67 No.49
<P>Photosynthetic cyanobacteria can fix CO<SUB>2</SUB> and utilize it as the sole carbon source for cell growth and production of biochemicals. Here, we metabolically engineered <I>Synechococcus elongatus</I> PCC 7942 for an enhanced production of α-farnesene by optimizing the ribosome-binding site (RBS) of the codon-optimized farnesene synthase gene. The production of α-farnesene was found to be enhanced in strains with a low translation initiation rate, resulting in α-farnesene production (0.57 mg/(L day)). Using the RBS variants and random mutations, we performed fluorescence-based analysis of cells grown in 96-well culture plates to screen the α-farnesene-producing strains but could not improve the titers of the RBS-optimized strains. However, evolutionary engineering of the RBS-optimized strains resulted in a twofold increase in α-farnesene production (1.2 mg/(L day)) compared to the previous study. Therefore, combining metabolic and evolutionary engineering might be helpful for enhancing the cellular fitness of cyanobacteria for the production of target chemicals.</P> [FIG OMISSION]</BR>
Juntarajumnong, Waraporn,Eaton-Rye, Julian J.,Incharoensakdi, Aran Korean Society for Biochemistry and Molecular Biol 2007 Journal of biochemistry and molecular biology Vol.40 No.5
The two-component signal transduction, which typically consists of a histidine kinase and a response regulator, is used by bacterial cells to sense changes in their environment. Previously, the SphS-SphR histidine kinase and response regulator pair of phosphate sensing signal transduction has been identified in Synechocystis sp. PCC 6803. In addition, some response regulators in bacteria have been shown to be cross regulated by low molecular weight phosphorylated compounds in the absence of the cognate histidine kinase. The ability of an endogenous acetyl phosphate to phosphorylate the response regulator, SphR in the absence of the cognate histidine kinase, SphS was therefore tested in Synechocystis sp. PCC 6803. The mutant lacking functional SphS and acetate kinase showed no detectable alkaline phosphatase activity under phosphate-limiting growth conditions. The results suggested that the endogenous acetyl phosphate accumulated inside the mutants could not activate the SphR via phosphorylation. On the other hand, exogenous acetyl phosphate could allow the mutant lacking functional acetate kinase and phosphotransacetylase to grow under phosphate-limiting conditions suggesting the role of acetyl phosphate as an energy source. Reverse transcription PCR demonstrated that the transcripts of acetate kinase and phospho-transacetylase genes in Synechocystis sp. PCC 6803 is up-regulated in response to phosphate limitation suggesting the importance of these two enzymes for energy metabolism in Synechocystis cells