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1. Reconstructing electron transfer components from an Fe(II) oxidizing bacterium

   https://doi.org/10.1099/mic.0.001240  

   Jain, Abhiney ; Kalb, Madison J. ; Gralnick, Jeffrey A. ( September 2022 , Microbiology)

   Neutrophilic Fe(II) oxidizing bacteria play an important role in biogeochemical processes and have also received attention for multiple technological applications. These micro-organisms are thought to couple their metabolism with extracellular electron transfer (EET) while oxidizing Fe(II) as electron donor outside the cell. Sideroxydans lithotrophicus ES-1 is a freshwater chemolithoautotrophic Fe(II) oxidizing bacterium that is challenging to culture and not yet genetically tractable. Analysis of the S. lithotrophicus ES-1 genome predicts multiple EET pathways, which are proposed to be involved in Fe(II) oxidation, but not yet validated. Here we expressed components of two of the proposed EET pathways, including the Mto and Slit_0867–0870 PCC3 pathways , from S. lithotrophicus ES-1 into Aeromonas hydrophila , an established model EET organism. We demonstrate that combinations of putative inner membrane and periplasmic components from the Mto and Slit_0867–0870 PCC3 pathways partially complemented EET activity in Aeromonas mutants lacking native components. Our results provide evidence for electron transfer functionality and interactions of inner membrane and periplasmic components from the Mto and Slit_0867–0870 PCC3 pathways. Based on these findings, we suggest that EET in S. lithotrophicus ES-1 could be more complicated than previously considered and raises questions regarding directionality of these electron transfer pathways. 

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2. A hybrid transistor with transcriptionally controlled computation and plasticity

   https://doi.org/10.1038/s41467-024-45759-1  

   Gao, Yang ; Zhou, Yuchen ; Ji, Xudong ; Graham, Austin J. ; Dundas, Christopher M. ; Miniel Mahfoud, Ismar E. ; Tibbett, Bailey M. ; Tan, Benjamin ; Partipilo, Gina ; Dodabalapur, Ananth ; et al ( February 2024 , Nature Communications)

   Organic electrochemical transistors (OECTs) are ideal devices for translating biological signals into electrical readouts and have applications in bioelectronics, biosensing, and neuromorphic computing. Despite their potential, developing programmable and modular methods for living systems to interface with OECTs has proven challenging. Here we describe hybrid OECTs containing the model electroactive bacteriumShewanella oneidensisthat enable the transduction of biological computations to electrical responses. Specifically, we fabricated planar p-type OECTs and demonstrated that channel de-doping is driven by extracellular electron transfer (EET) fromS. oneidensis. Leveraging this mechanistic understanding and our ability to control EET flux via transcriptional regulation, we used plasmid-based Boolean logic gates to translate biological computation into current changes within the OECT. Finally, we demonstrated EET-driven changes to OECT synaptic plasticity. This work enables fundamental EET studies and OECT-based biosensing and biocomputing systems with genetically controllable and modular design elements.

    

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3. Intramolecular Vibrations in Excitation Energy Transfer: Insights from Real-Time Path Integral Calculations

   https://doi.org/10.1146/annurev-physchem-090419-120202  

   Kundu, Sohang ; Makri, Nancy ( April 2022 , Annual Review of Physical Chemistry)

   Excitation energy transfer (EET) is fundamental to many processes in chemical and biological systems and carries significant implications for the design of materials suitable for efficient solar energy harvest and transport. This review discusses the role of intramolecular vibrations on the dynamics of EET in nonbonded molecular aggregates of bacteriochlorophyll, a perylene bisimide, and a model system, based on insights obtained from fully quantum mechanical real-time path integral results for a Frenkel exciton Hamiltonian that includes all vibrational modes of each molecular unit at finite temperature. Generic trends, as well as features specific to the vibrational characteristics of the molecules, are identified. Weak exciton-vibration (EV) interaction leads to compact, near-Gaussian densities on each electronic state, whose peak follows primarily a classical trajectory on a torus, while noncompact densities and nonlinear peak evolution are observed with strong EV coupling. Interaction with many intramolecular modes and increasing aggregate size smear, shift, and damp these dynamical features. 

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4. Widespread extracellular electron transfer pathways for charging microbial cytochrome OmcS nanowires via periplasmic cytochromes PpcABCDE

   https://doi.org/10.1038/s41467-024-46192-0  

   Portela, Pilar C. ; Shipps, Catharine C. ; Shen, Cong ; Srikanth, Vishok ; Salgueiro, Carlos A. ; Malvankar, Nikhil S. ( March 2024 , Nature Communications)

   Extracellular electron transfer (EET) via microbial nanowires drives globally-important environmental processes and biotechnological applications for bioenergy, bioremediation, and bioelectronics. Due to highly-redundant and complex EET pathways, it is unclear how microbes wire electrons rapidly (>10⁶s⁻¹) from the inner-membrane through outer-surface nanowires directly to an external environment despite a crowded periplasm and slow (<10⁵s⁻¹) electron diffusion among periplasmic cytochromes. Here, we show thatGeobacter sulfurreducensperiplasmic cytochromes PpcABCDE inject electrons directly into OmcS nanowires by binding transiently with differing efficiencies, with the least-abundant cytochrome (PpcC) showing the highest efficiency. Remarkably, this defined nanowire-charging pathway is evolutionarily conserved in phylogenetically-diverse bacteria capable of EET. OmcS heme reduction potentials are within 200 mV of each other, with a midpoint 82 mV-higher than reported previously. This could explain efficient EET over micrometres at ultrafast (<200 fs) rates with negligible energy loss. Engineering this minimal nanowire-charging pathway may yield microbial chassis with improved performance.

    

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5. Amorphous silicates as a record of solar nebular and parent body processes—A transmission electron microscope study of fine‐grained rims and matrix in three Antarctic CR chondrites

   https://doi.org/10.1111/maps.13526  

   Vollmer, Christian ; Pelka, Mandy ; Leitner, Jan ; Janssen, Arne ( June 2020 , Meteoritics & Planetary Science)

   Renazzo‐type (CR) carbonaceous chondrites belong to one of the most pristine meteorite groups containing various early solar system components such as matrix and fine‐grained rims (FGRs), whose formation mechanisms are still debated. Here, we have investigated FGRs of three Antarctic CR chondrites (GRA 95229, MIL 07525, and EET 92161) by electron microscopy techniques. We specifically focused on the abundances and chemical compositions of the amorphous silicates within the rims and matrix by analytical transmission electron microscopy. Comparison of the amorphous silicate composition to a matrix area of GRA 95229 clearly shows a compositional relationship between the matrix and the fine‐grained rim, such as similar Mg/Si and Fe/Si ratios. This relationship and the abundance of the amorphous silicates in the rims strengthen a solar nebular origin and rule out a primary formation mechanism by parent body processes such as chondrule erosion. Moreover, our chemical analyses of the amorphous silicates and their abundance indicate that the CR rims experienced progressive alteration stages. According to our analyses, the GRA 95229 sample is the least altered one based on its high modal abundance of amorphous silicates (31%) and close‐to‐chondritic Fe/Si ratios, followed by MIL 07525 and finally EET 92161 with lesser amounts of amorphous silicates (12% and 5%, respectively) and higher Fe/Si ratios. Abundances and chemical compositions of amorphous silicates within matrix and rims are therefore suitable recorders to track different alteration stages on a submicron scale within variably altered CR chondrites.

    

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