Lutein Production by Halophilic Microalgae Using Anaerobic Digestate as the Substrate and Its Potential Application as a Biopesticide.

Production of value-added products from waste anaerobic digestate is economically and environmentally important for sustainable development of industrial process and products. In this study halophilic microalgae, Chlorella vulgaris 92001, Chlorella vulgaris 50291, Chlorella vulgaris 10241 and Tetraselmis indica, were initially screened for lutein production using synthetic dairy digestate (DD), municipal digestate (MD) and poultry digestate (PD) as no-cost substrates. Screening and optimization of parameters, such as dilution, pH, MgCl2, NaCl, NaHCO3 and inoculum concentration for maximum lutein production were further performed employing statistically designed Plackett-Burman and response surface methodology. Cultivation of C. vulgaris 92001 in a split column photobioreactor under optimum culture condition showed increase in lutein production by 2.36-fold in batch mode. The influence of different hydraulic retention time (HRT) values of 150, 130, 100 and 90 h on lutein production was evaluated in continuous mode with the split column photobioreactor. Lutein produced using the synthetic poultry digestate showed good potential biopesticide activity against Spodoptera litura (fall armyworm). Overall, this study demonstrated bioprocess development to produce lutein using synthetic anaerobic digestate from marine algae and its potential application as a biopesticide.

Bioelectricity production and shortcut nitrogen removal by microalgal-bacterial consortia using membrane photosynthetic microbial fuel cell.

Membrane photosynthetic microbial fuel cell (MPMFC) utilizes O2, NO3- and NO2- as cathodic electron acceptors, enabling simultaneous treatment of nitrogen, CO2 and organic carbon in the cathode compartment. In this work, development of a novel cathodic process with in situ nitritation via microalgal photosynthesis during the light period is reported for achieving shortcut nitrogen removal (SNR) from ammonium-rich wastewater. Moreover, a tubular low-cost ceramic membrane was used to separate and recycle the microalgal-bacterial biomass to the cathode compartment during the continuous operation. The influence of NH4+ concentration and ratio of chemical oxygen demand to total nitrogen on the MPMFC performance was examined. Denitritation under dark and anoxic conditions occurred due to denitrifying bacteria (DNB) subsequent to nitritation under light and aerobic conditions by ammonia-oxidizing bacteria (AOB) in the consortia. Final concentrations of NH4+ and NO2- in the effluent of 0.10 mg NH4+-L-1 and 0.02 mg NO2--L-1, respectively, were obtained using MPMFC which resulted in a nitrogen removal efficiency of 99 ± 0.5%. The maximum electricity production achieved using the MPMFC was 56 ± 0.1 mA. This study demonstrated that combining microalgal photosynthesis, nitritation and denitritation in the cathode compartment of MPMFC is advantageous for avoiding the cost due to external aeration and organic carbon source necessary for ammonium removal as well as utilization of NO2- or NO3- as an electron acceptor.

Acute toxicity of cyanide in aerobic respiration: Theoretical and experimental support for murburn explanation.

The inefficiency of cyanide/HCN (CN) binding with heme proteins (under physiological regimes) is demonstrated with an assessment of thermodynamics, kinetics, and inhibition constants. The acute onset of toxicity and CN's mg/Kg LD50 (µM lethal concentration) suggests that the classical hemeFe binding-based inhibition rationale is untenable to account for the toxicity of CN. In vitro mechanistic probing of CN-mediated inhibition of hemeFe reductionist systems was explored as a murburn model for mitochondrial oxidative phosphorylation (mOxPhos). The effect of CN in haloperoxidase catalyzed chlorine moiety transfer to small organics was considered as an analogous probe for phosphate group transfer in mOxPhos. Similarly, inclusion of CN in peroxidase-catalase mediated one-electron oxidation of small organics was used to explore electron transfer outcomes in mOxPhos, leading to water formation. The free energy correlations from a Hammett study and IC50/Hill slopes analyses and comparison with ligands ( CO/ H 2 S/ N 3 - ) $\left( {\text{CO}}/{{{{\text{H}}_{2}}\text{S}}/{\text{N}_{3}^{\text{-}}}\;}\; \right)$ provide insights into the involvement of diffusible radicals and proton-equilibriums, explaining analogous outcomes in mOxPhos chemistry. Further, we demonstrate that superoxide (diffusible reactive oxygen species, DROS) enables in vitro ATP synthesis from ADP+phosphate, and show that this reaction is inhibited by CN. Therefore, practically instantaneous CN ion-radical interactions with DROS in matrix catalytically disrupt mOxPhos, explaining the acute lethal effect of CN.

Chemiosmotic and murburn explanations for aerobic respiration: Predictive capabilities, structure-function correlations and chemico-physical logic.

Since mid-1970s, the proton-centric proposal of 'chemiosmosis' became the acclaimed explanation for aerobic respiration. Recently, significant theoretical and experimental evidence were presented for an oxygen-centric 'murburn' mechanism of mitochondrial ATP-synthesis. Herein, we compare the predictive capabilities of the two models with respect to the available information on mitochondrial reaction chemistry and the membrane proteins' structure-function correlations. Next, fundamental queries are addressed on thermodynamics of mitochondrial oxidative phosphorylation (mOxPhos): (1) Can the energy of oxygen reduction be utilized for proton transport? (2) Is the trans-membrane proton differential harness-able as a potential energy capable of doing useful work? and (3) Whether the movement of miniscule amounts of mitochondrial protons could give rise to a potential of ~200 mV and if such an electrical energy could sponsor ATP-synthesis. Further, we explore critically if rotary ATPsynthase activity of Complex V can account for physiological ATP-turnovers. We also answer the question- "What is the role of protons in the oxygen-centric murburn scheme of aerobic respiration?" Finally, it is demonstrated that the murburn reaction model explains the fast kinetics, non-integral stoichiometry and high yield of mOxPhos. Strategies are charted to further demarcate the two explanations' relevance in the cellular physiology of aerobic respiration.

Aerobic respiration: proof of concept for the oxygen-centric murburn perspective.

The inner mitochondrial membrane protein complexes (I-V) and prokaryotic respiratory machinery are examined for a deeper understanding of their structure-function correlations and dynamics. In silico analysis of the structure of complexes I-IV, docking studies and erstwhile literature confirm that they carry sites which are in close proximity to DROS (diffusible reactive oxygen species) generating redox centers. These findings provide supportive evidence for the newly proposed oxygen-centric chemical-coupling mechanism (murburn concept), wherein DROS catalyzes the esterification of inorganic phosphate to ADP. Further, in a reductionist system, we demonstrate that a DROS (like superoxide) can effectively esterify inorganic phosphate to ADP. The impact of these findings and the interactive dynamics of classical inhibitors (rotenone and cyanide), uncouplers (dinitrophenol and uncoupling protein) and other toxins (atractyloside and oligomycin) are briefly discussed. Highlights • Earlier perception: Complexes (I-IV) pump protons and Complex V make ATP (aided by protons) • Herein: Respiratory molecular machinery is probed for new structure-function correlations • Analyses: Quantitative arguments discount proton-centric ATP synthesis in mitochondria and bacteria • In silico data: ADP-binding sites and O2/ diffusible reactive oxygen species (DROS)-accessible channels are unveiled in respiratory proteins • In vitro data: Using luminometry, ATP synthesis is demonstrated from ADP, Pi and superoxide • Inference: Findings agree with decentralized ADP-Pi activation via oxygen-centric murburn scheme Communicated by Ramaswamy H. Sarma.