Biotransformation of Heavy Metals from Soil in Synthetic Medium Enriched with Glucose and Shewanella sp. HN-41 at Various pH

The biotransformation of heavy metals from contaminated soil was examined using a facultative anaerobic bacterium Shewanella sp. HN-41. The experiments were carried out to assess the influence of glucose at various pH on the transformation of heavy metals from soil thorough solubilization. A preliminary study on the transformation of heavy metals from soil was first performed using a defined medium supplemented with glucose at 10, 20, and 30 mM to select the effective concentration. Among the three concentrations examined, glucose at 30 mM leached a highest level of metal ions. Therefore, 30 mM glucose was used as the representative carbon source for the subsequent experiments in a defined medium at various pH (5, 6, 7, 8, and 9). The organism HN-41 was not influenced by pH ranging from acidic to neutral and was able to metabolize all the metal elements from contaminated soil. The level of Fe, Cr, As, Mn, Pb, and Al solubilization ranged from 3 to 7664 mg kg^?1 at various initial pH. The rate of metal solubilization was found to be low at neutral pH compared with acidic and alkaline. These results are expected to assist in the development of heavy metal transformation processes for the decontamination of heavy metal-contaminated soil.     

Redox Buffer Capacity in Water-Rock-Microbe Interaction Systems in Subsurface Environments

An incubation experiment was conducted to estimate redox buffer capacity of “water-rock-microbe” interaction systems in sedimentary rocks. The water chemistry, microbial growth and community structure were analyzed during the incubations. The dissolved oxygen (DO) concentrations and oxidation-reduction potential (ORP) values decreased notably in the presence of active microorganisms, whereas abiotic reactions did not lead to reducing conditions during incubation. The change in microbial community structure suggests that nitrate-reducing and sulfate-reducing bacteria played an important role in reduction of water by using lignite-derived organic matter. These results show that the microbial role is extremely important for the redox buffering capacity in sedimentary rock environments.     

Minireview: The Potential of Enhanced Manganese Redox Cycling for Sediment Oxidation

Both natural and anthropogenic processes are responsible for excessive organic loading of submerged soils, with detrimental environmental consequences. The often insufficient natural attenuation can be enhanced by exploiting microbial manganese cycles. This review describes how an anoxic oxidation of organic matter with concomitant reduction of MnO ₂ can link up with a reoxidation of the resulting, soluble Mn(II) in oxic layers. The potentially attainable oxidation rates through these natural cycles are of the same order as the organic carbon accumulation rates. The microbiology and physiology of the responsible organisms are discussed, as well as examples of naturally occurring manganese cycles and the possibility to engineer this natural phenomenon.     

Reassessment of the Microbial Role in Mn-Fe Nodule Genesis in Andean Paleosols

The presence of Mn-Fe nodules in the epipedons (surface horizons) of paleosols of presumed Upper Neogene age in the northwestern Venezuelan Andes have been interpreted as products of inorganic oxidation and reduction processes operating over the full range of glacial and interglacial cycles that affected paleosol morphogenesis. New microscopic/chemical data from combined SEM-EDS-FIB analyses of representative Mn-Fe nodules indicate microbes play an important role in Mn/Fe precipitation leading to their genesis in alpine Mollisols (Argiustolls). Although the prevailing new data are based mainly on fossil forms of filamentous bacteria and fungi and other biogenic pseudomorphs that may represent the former resident bacteria, the presence of extant microbes must await field experiments/collection, followed by a molecular microbiology approach to determine the biological drivers of metal precipitation. As in other terrestrial niche environments, microbes are seen here to play a role, perhaps a key one, in the morphogenesis of paleosols of importance in upper Neogene paleoenvironmental reconstruction.     

Introduction to the Thematic Minireview Series on Redox-active Protein Modifications and Signaling

The dynamics of redox metabolism necessitate cellular strategies for sensing redox changes and for responding to them. A common mechanism for receiving and transmitting redox changes is via reversible modifications of protein cysteine residues. A plethora of cysteine modifications have been described, including sulfenylation, glutathionylation, and disulfide formation. These post-translational modifications have the potential to alter protein structure and/or function and to modulate cellular processes ranging from division to death and from circadian rhythms to secretion. The focus of this thematic minireview series is cysteine modifications in response to reactive oxygen and nitrogen species.     

Stepwise reduction of the culture redox potential allows the analysis of microaerobic metabolism and photosynthetic membrane synthesis in Rhodospirillum rubrum

Bacterial growth under oxygen‐limited (microaerobic) conditions is often accompanied by phenomena of great interest for fundamental research and industrial application. The microaerobic lifestyle of anoxygenic photosynthetic bacteria like Rhodospirillum rubrum harbors such a phenomenon, as it allows the formation of photosynthetic membranes and related interesting products without light. However, due to the technical difficulties in process control of microaerobic cultivations and the limited sensitivity of available oxygen sensors, the analysis of microaerobic growth and physiology is still underrepresented in current research. The main focus of the present study was to establish an experimental set‐up for the systematic study of physiological processes, associated with the growth of R. rubrum under microaerobic conditions in the dark. For this purpose, we introduce a robust and reliable microaerobic process control strategy, which applies the culture redox potential (CRP) for assessing different degrees of oxygen limitation in bioreactor cultivations. To describe the microaerobic growth behavior of R. rubrum cultures for each of these defined CRP reduction steps, basic growth parameters were experimentally determined. Flux variability analysis provided an insight into the metabolic activity of the TCA cycle and implied its connection to the respiratory capacity of the cells. In this context, our results suggest that microaerobic growth of R. rubrum can be described as an oxygen‐activated cooperative mechanism. The present study thus contributes to the investigation of metabolic and regulatory events responsible for the redox‐sensitive formation of photosynthetic membranes in facultative photosynthetic bacteria. Furthermore, the introduced microaerobic cultivation setup should be generally applicable for any microbial system of interest which can be cultivated in common stirred‐tank bioreactors. Biotechnol. Bioeng. 2013; 110: 573–585. © 2012 Wiley Periodicals, Inc.     

Why did eukaryotes evolve only once? Genetic and energetic aspects of conflict and conflict mediation

According to multi-level theory, evolutionary transitions require mediating conflicts between lower-level units in favour of the higher-level unit. By this view, the origin of eukaryotes and the origin of multicellularity would seem largely equivalent. Yet, eukaryotes evolved only once in the history of life, whereas multicellular eukaryotes have evolved many times. Examining conflicts between evolutionary units and mechanisms that mediate these conflicts can illuminate these differences. Energy-converting endosymbionts that allow eukaryotes to transcend surface-to-volume constraints also can allocate energy into their own selfish replication. This principal conflict in the origin of eukaryotes can be mediated by genetic or energetic mechanisms. Genome transfer diminishes the heritable variation of the symbiont, but requires the de novo evolution of the protein-import apparatus and was opposed by selection for selfish symbionts. By contrast, metabolic signalling is a shared primitive feature of all cells. Redox state of the cytosol is an emergent feature that cannot be subverted by an individual symbiont. Hypothetical scenarios illustrate how metabolic regulation may have mediated the conflicts inherent at different stages in the origin of eukaryotes. Aspects of metabolic regulation may have subsequently been coopted from within-cell to between-cell pathways, allowing multicellularity to emerge repeatedly.     

A novel hearing specialization in the New Zealand bigeye,Pempheris adspersa

The New Zealand bigeye, Pempheris adspersa, is a nocturnal planktivore and has recently been found to be an active sound producer. The rostral end of the swim bladder lies adjacent to Baudelot''s ligament which spans between the bulla and the cleithrum bone of the pectoral girdle. The aim of this study was to use the auditory evoked potential technique to physiologically test the possibility that this structure provides an enhanced sensitivity to sound pressure in the bigeye. At 100 Hz, bigeye had hearing sensitivity similar to that of goldfish (species with a mechanical connection between the swim bladder and the inner ear mediated by the Weberian ossicles) and were much more sensitive than other teleosts without ancillary hearing structures. Severing Baudelot''s ligament bilaterally resulted in a marked decrease in hearing sensitivity, as did swim bladder puncture or lateral line blockage. These results show that bigeye have an enhanced sensitivity to sound pressure and provide experimental evidence that the functional basis of this sensitivity represents a novel hearing specialization in fish involving the swim bladder, Baudelot''s ligament and the lateral line.     

Redox Shuttles with Axisymmetric Scaffold for Overcharge Protection of Lithium‐Ion Batteries

The derivatives of 1,4‐dimethoxybenzene are thus far the best performing redox shuttle additives for overcharge protection of Li‐ion batteries. The most durable molecules of this kind typically possess two in‐plane methoxy groups that are equivalent by inversion symmetry. However, such geometry leads to a vanishing average dipole moment that causes poor solubility of these molecules in carbonate‐based electrolytes. In this study, a novel redox shuttle additive, 1,2,3,4‐tetrahydro‐6,7‐dimethoxy‐1,1,4,4‐tetramethyl‐naphthalene (TDTN), is introduced. It has been demonstrated that reversible oxidation at 4.05 V versus Li⁺/Li, high polarity, high solubility (around 0.4 m ), and excellent electrochemical stability (150 overcharge cycles at C/2 rate with 100% overcharge) can all be achieved simultaneously by the imposition of axial symmetry in the corresponding radical cation that is generated by electrochemical oxidation of TDTN in the battery. The intricate interplay between the symmetry and the chemical stability of the radical cation is scrutinized using magnetic resonance spectroscopy and electron structure modeling.     

A High‐Energy‐Density Multiple Redox Semi‐Solid‐Liquid Flow Battery

A new concept of multiple redox semi‐solid‐liquid (MRSSL) flow battery that takes advantage of active materials in both liquid and solid phases, is proposed and demonstrated. Liquid lithium iodide (LiI) electrolyte and solid sulfur/carbon (S/C) composite, forming LiI‐S/C MRSSL catholyte, are employed to demonstrate this concept. Record volumetric capacity (550 Ah L^?1_catholyte) is achieved using highly concentrated and synergistic multiple redox reactions of LiI and sulfur. The liquid LiI electrolyte is found to increase the reversible volumetric capacity of the catholyte, improve the electrochemical utilization of the S/C composite, and reduce the viscosity of catholyte. A continuous flow test is demonstrated and the influence of the flow rate on the flow battery performance is discussed. The MRSSL flow battery concept transforms inactive component into bi‐functional active species and creates synergistic interactions between multiple redox couples, offering a new direction and wide‐open opportunities to develop high‐energy‐density flow batteries.