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1. In Situ Conformational Changes of the Escherichia coli Serine Chemoreceptor in Different Signaling States

   https://doi.org/10.1128/mBio.00973-19  

   Yang, Wen ; Cassidy, C. Keith ; Ames, Peter ; Diebolder, Christoph A. ; Schulten, Klaus ; Luthey-Schulten, Zaida ; Parkinson, John S. ; Briegel, Ariane ; Harwood, Caroline S. ( August 2019 , mBio)

   ABSTRACT Tsr, the serine chemoreceptor in Escherichia coli , transduces signals from a periplasmic ligand-binding site to its cytoplasmic tip, where it controls the activity of the CheA kinase. To function, Tsr forms trimers of homodimers (TODs), which associate in vivo with the CheA kinase and CheW coupling protein. Together, these proteins assemble into extended hexagonal arrays. Here, we use cryo-electron tomography and molecular dynamics simulation to study Tsr in the context of a near-native array, characterizing its signaling-related conformational changes at both the individual dimer and the trimer level. In particular, we show that individual Tsr dimers within a trimer exhibit asymmetric flexibilities that are a function of the signaling state, highlighting the effect of their different protein interactions at the receptor tips. We further reveal that the dimer compactness of the Tsr trimer changes between signaling states, transitioning at the glycine hinge from a compact conformation in the kinase-OFF state to an expanded conformation in the kinase-ON state. Hence, our results support a crucial role for the glycine hinge: to allow the receptor flexibility necessary to achieve different signaling states while also maintaining structural constraints imposed by the membrane and extended array architecture. IMPORTANCE In Escherichia coli , membrane-bound chemoreceptors, the histidine kinase CheA, and coupling protein CheW form highly ordered chemosensory arrays. In core signaling complexes, chemoreceptor trimers of dimers undergo conformational changes, induced by ligand binding and sensory adaptation, which regulate kinase activation. Here, we characterize by cryo-electron tomography the kinase-ON and kinase-OFF conformations of the E. coli serine receptor in its native array context. We found distinctive structural differences between the members of a receptor trimer, which contact different partners in the signaling unit, and structural differences between the ON and OFF signaling complexes. Our results provide new insights into the signaling mechanism of chemoreceptor arrays and suggest an important functional role for a previously postulated flexible region and glycine hinge in the receptor molecule. 

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2. Flexible Platform for In Situ Impedimetric Detection and Bioelectric Effect Treatment of Escherichia Coli Biofilms

   https://doi.org/10.1109/TBME.2018.2872896  

   Huiszoon, Ryan C. ; Subramanian, Sowmya ; Ramiah Rajasekaran, Pradeep ; Beardslee, Luke A. ; Bentley, William E. ; Ghodssi, Reza ( May 2019 , IEEE Transactions on Biomedical Engineering)
3. Emerging investigator series: interacting effects of environmental factors on Daphnia magna removal of Escherichia coli from wastewater

   https://doi.org/10.1039/D1EW00008J  

   Abtahi, Seyyed M. ; Aryal, Ojaswi ; Ismail, Niveen S. ( January 2021 , Environmental Science: Water Research & Technology)

   null (Ed.)

   Treatment wetlands can remove a wide range of pollutants from wastewater and stormwater runoff, including microbial pollutants such as Escherichia coli . Filter feeding zooplankton play an important role in improving water quality in treatment wetlands through grazing and subsequent inactivation of E. coli . Understanding how climate change will impact the various processes governing microbial inactivation in treatment wetlands is essential to ensure adequately treated water. We investigated the impact of interacting environmental factors on the E. coli clearance rate of a keystone zooplankton species, Daphnia magna . We utilized a full factorial experimental design to test the impacts of food abundance, food type, and temperature in flow-through mesocosms under environmentally relevant conditions. Temperature and food abundance interactions were significant, which highlights the importance of studying multiple environmental variables when considering the filter feeding contributions of zooplankton. While both food abundance and temperature had a significant impact on clearance rate, daphnids did not exhibit a preference between algae or E. coli , which were the two food sources used in our studies. We observed that at 25 °C, food abundance and type had a larger impact on E. coli clearance rate than at 15 °C, which has important implications when considering resiliency of treatment wetlands in a warming climate. Our findings show that zooplankton filtration behavior will be impacted by environmental conditions that are projected due to climatic changes, but populations can still inactivate E. coli and improve water quality when exposed to these conditions. 

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4. Plasmid‐encoded protein attenuates Escherichia coli swimming velocity and cell growth, not reprogrammed regulatory functions

   https://doi.org/10.1002/btpr.2778  

   Virgile, Chelsea ; Hauk, Pricila ; Wu, Hsuan‐Chen ; Bentley, William E. ( February 2019 , Biotechnology Progress)

   In addition to engineering new pathways for synthesis, synthetic biologists rewire cells to carry out “programmable” functions, an example being the creation of wound‐healing probiotics. Engineering regulatory circuits and synthetic machinery, however, can be deleterious to cell function, particularly if the “metabolic burden” is significant. Here, a synthetic regulatory circuit previously constructed to directEscherichiacolito swim toward hydrogen peroxide, a signal of wound generation, was shown to work even with coexpression of antibiotic resistance genes and genes associated with lactose utilization. We found, however, that cotransformation with a second vector constitutively expressing GFP (as a marker) and additionally conferring resistance to kanamycin and tetracycline resulted in slower velocity (Δ~6 μm/s) and dramatically reduced growth rate (Δ > 50%). The additional vector did not, however, alter the run‐and‐tumble ratio or directional characteristics of H₂O₂–dependent motility. The main impact of this additional burden was limited to slowing cell velocity and growth, suggesting that reprogrammed cell motility by minimally altering native regulatory circuits can be maintained even when extraneous burden is placed on the host cell. © 2019 American Institute of Chemical EngineersBiotechnol. Prog., 35: e2778, 2019.

    

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5. Targeted Capture and Heterologous Expression of the Pseudoalteromonas Alterochromide Gene Cluster in Escherichia coli Represents a Promising Natural Product Exploratory Platform

   https://doi.org/10.1021/sb500280q  

   Ross, Avena C. ; Gulland, Lauren E. ; Dorrestein, Pieter C. ; Moore, Bradley S. ( April 2015 , ACS Synthetic Biology)