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Metabolic Engineering for the Production of a Variety of Biofuels and Biochemicals
Published in Kazuyuki Shimizu, Metabolic Regulation and Metabolic Engineering for Biofuel and Biochemical Production, 2017
Removal of three cytochrome oxidases (cyoABCD, cydAB, cbdAB (appBD)) and quinol mono-oxigenase (ygiN) results in the reduction of oxygen uptake rate by nearly 98%, and the activation of anaerobic respiration under oxic condition, where the content of quinone pool shifts from ubiquinones (UQs) to menaquinones (MQs), which in turn activates ArcA, which causes the repression of the TCA cycle activity (Portnoy et al. 2010). In this case, the specific growth rate decreased from 0.71 h-1 (K12 MG1655) to 0.32 h-1, while the specific glucose uptake rate increased from 9.02 mmol/gDCW.h to 26.4 mmol/gDCW.h, and the lactate production rate was nearly 48.6 mmol/gDCW.h (0.98 g/g glucose) without acetate formation (3.37 mmol/gDCW.h in the wild type strain) (Portnoy et al. 2010). The reason why the specific glucose uptake rate was increased may be the disruption of the cytochromes in the respiratory chain as mentioned in Chaprer 4. In this strain, anaerobic respiration occurs by the respiratory chain formed by NADH: menaquinone oxide reductase (yieF and wrbA) and fumarate reductase (frdABCD), where electrons are transferred from NADH to fumarate to menaquinone pool (Yagi and Matsuno-Yagi 2003), resulting in the formation of succinate (Portnoy et al. 2010). Unlike the case of anaerobic conditions, Fnr is not active under oxic conditions, while ArcA is active as stated above, and thus pfl operon may not be active without producing formate in this strain, where pfl operon is co-regulated by both ArcA and Fnr.
Production of Life-Saving Drugs from Marine Sources
Published in Prasenjit Mondal, Ajay K. Dalai, Sustainable Utilization of Natural Resources, 2017
Bioactivity guided fractionation and isolation of the ethanol extract of sponges Amphimedon spp. (LD50 4.0 μg/mL and LD99 130 μg/mL) against nematode Haemonchus contortus resulted in the isolation of macrocyclic lactone and lactams. Amphilactams A–D (89–92), exhibited in vitro LD99 activities at 7.5, 47, 8.5, and 0.39 μg/mL, respectively. These compounds restrain larval development at the L1 stage of nematode Haemonchus contortus but no activity against nematode eggs (Ovenden et al. 1999). Geodin A Mg salt (93), chemically macrocyclic polyketide lactam tetramic acid, is a potent nematocide isolated from southern Australian marine sponge Geodia. Geodin A which exists as Mg salt in a natural source was found to be nematocidal to Haemonchus contortus with LD99 value of 1 μg/mL (Capon et al. 1999). Bislobane (94) obtained from red alga Laurencia scoparia displayed weak anthelmintic activity with an EC50 of 0.11 mM against the parasitant stage (L4) of a rat gastrointestinal parasite Nippostrongylus brasiliensis, which is similar to human parasite hookworms (Davyt et al. 2006). Nafuredin (95) is produced by a fungus Aspergillus niger FT-0554 isolated from a marine sponge, as well as cultured broth of the strain FT-0554. Nafuredin (95) inhibited NADH-fumarate reductase (complexes I+II) from adult Ascaris suum (pig roundworm) at IC50 of 12 nM. NADH-fumarate reductase is an important enzyme involved in the electron transport system of anaerobic metabolism found in many anaerobic organisms (Omura et al. 2001). Nafuredin (95) also showed anthelmintic activity against Haemonchus contortus (wireworm) in in vivo trials with sheep (Ui et al. 2001). Significant nematocidal (LD99 5.2 μg/mL) activity against parasitic nematode Haemonchus contortus was exhibited by onnamide F (96), a marine NP isolated from marine sponge, Trachycladus laevispirulifer. Onnamide F (96) was also active against S. cerevisiae with LD99 value of 1.4 μg/mL (Vuong et al. 2001). (−)-echinobetaine A (97; Capon et al. 2005a) and (+)-echinobetaine B (98; Capon et al. 2005b) are betaine-type nematocidal agents present in a southern Australian marine sponge of the genus Echinodictyum. (−)-echinobetaine A (97) and (+)-echinobetaine B (98) are nematocidal (LD99 83 and 8.3 μg/mL, respectively) to the parasite Haemonchus contortus.
The mechanism and application of bidirectional extracellular electron transport in the field of energy and environment
Published in Critical Reviews in Environmental Science and Technology, 2021
Qingqing Xie, Yue Lu, Lin Tang, Guangming Zeng, Zhaohui Yang, Changzheng Fan, Jingjing Wang, Siavash Atashgahi
The intracellular oxidation of electron donors in Shewanella species is coupled with extracellular reduction of metals (such as iron and manganese oxides) through the metal respiratory (Mtr) pathway (Figure 1A) (White et al., 2013). During the initial state of EET, the oxidation of quinol to quinone releases electrons on the inner face of the cytoplasmic membrane. Then CymA, a tetraheme c-Cyt located on the outer face of the cytoplasmic membrane, delivers electrons from the quinone pool to the periplasmic space (Marritt et al., 2012). Once in periplasm, free MtrA diffusing in periplasm transfers electrons to the MtrCAB complex located in the outer membrane. Periplasmic FccA (fumarate reductase) and STC (small tetrahaem cytochrome) in association with free MtrA also bridge the periplasmic gap between CymA and the MtrCAB complex (Fonseca et al., 2013; Schuetz et al., 2009; Sturm et al., 2015). When electrons reach the outer membrane, the MtrCAB complex mediates transmembrane transport of electrons by forming channels (Richardson et al., 2012). MtrDEF complex, the modular paralogs of MtrCAB, has also been used as another transmembrane complex for electron transfer across the outer membrane of S. oneidensis MR-1 (Barrozo et al., 2018). Using electronic structure calculations and molecular simulations, MtrC and MtrF, the two decaheme c-Cyts located on the outer face of the outer membrane, have been found to reversibly transfer electron with similar efficiency to support bidirectional EET (Jiang et al., 2019). Moreover, the outer-membrane c-Cyt OmcA directly interacts with the insoluble substrates to achieve electron transfer at the microbe-acceptor interface. Direct evidence by electron cryotomography (ECT) elucidated that the structures of nanowires, the filamentous structures in Shewanella, were in fact chains formed by interconnected outer membrane vesicles with decaheme c-Cyts (presumably MtrA and MtrC distributed inside and outside of the outer membrane, respectively) (Figure 2A) (Subramanian et al., 2018). In addition, Shewanella species utilized self-secreted redox-active flavins, mainly riboflavin (RF) and flavin mononucleotide (FMN), as endogenous electron shuttles to accelerate indirect EET through their oxidation (Ox) and reduction (Red) cycle (Marsili et al., 2008). More specifically, FMN and RF as functional cofactors were bound to MtrC and OmcA, respectively (Okamoto et al., 2013).