Biology subjects

Christie, G.

Publications and source records attributed to Christie, G..

4 recordsLinked to original sources

bioRxiv2026

Liquid Phase Backscattered Scanning Electron Microscopy of Bacillus subtilis Spores

Backscattered electron scanning electron microscopy (BSE-SEM) provides compositional image contrast but has found limited application to biological samples due to the low atomic number difference between constituent elements, the thickness of the surrounding environment, and the need for complex sample preparation. Here, we demonstrate the use of room temperature liquid phase BSE-SEM (LPBSEM) for imaging Bacillus subtilis spores encapsulated in graphene liquid cells, preserving native hydration and reducing the thickness of the sample environment. This approach eliminates the need for staining and enables high-contrast visualisation of subcellular structures. Distinct structural layers within B. subtilis spores have been observed with a contrast similar to conventional thin-section transmission electron microscopy but without the need for sample preparation that potentially compromises sample integrity. We further investigate the influence of beam energy on the interaction volume depth and image contrast and propose optimal conditions for subsurface visualisation. Monte Carlo simulations have been used to validate our experimental observations and provide a quantitative framework for understanding BSE generation from hydrated, low atomic number specimens.

microbiology↗

bioRxiv2025

Expression of nano-engineered RNA organelles in bacteria

Designing synthetic biomolecular condensates, or membrane-less organelles, offers insights on the functions of their natural counterparts, and is equally valuable for cellular and metabolic engineering. Choosing E. coli for its biotechnological relevance, we deploy RNA nanotechnology to design and express non-natural membrane-less organelles in vivo. The designer condensates assemble co-transcriptionally from branched RNA motifs interacting via base-pairing. Exploiting binding selectivity we express orthogonal, non-mixing condensates, and by embedding a protein-binding aptamer we achieve selective protein recruitment. Condensates can be made to dissolve and re-assemble upon thermal cycling, thereby reversibly releasing and re-capturing protein clients. The synthetic organelles are expressed robustly across the cell population and remain stable despite enzymatic RNA processing. Compared with existing solutions based on peptide building blocks or repetitive RNA sequences, these nanostructured RNA motifs enable algorithmic control over interactions, affinity for clients, and condensate microstructure, opening new directions in synthetic biology and biotechnology.

synthetic biology↗

bioRxiv2025

Bioenergetic metabolism restarts alongside germinant sensing and hydration in bacterial spore germination

Bacterial spore germination transforms spores from dormant bodies to vegetative cells. Initiation of germination or spore rehydration can proceed without exogenous energy sources, so bioenergetic processes in germination have been overlooked, despite many germinants being energy sources, such as sugars. Here, we apply remission spectroscopy to noninvasively measure the energy-transducing electron-transport chain of intact spores during germination. In Bacillus megaterium and Bacillus subtilis, we find energisation of cytoplasmic metabolism and the electron transport chain occurs early in germination, before or alongside rehydration. The aa3-type oxidases (Qox, Cta) accumulate nonradical ferryl intermediates of their catalytic cycle demonstrating that the electron-transport chain is operating in a regime of high membrane potential. The Yth isoform of the bd oxidase is found in abundance in both organisms, functioning to allow rapid electron transfer to O2 when the aa3-type oxidases are hindered, establishing a new role for this enzyme beyond O2-scavenging. Deletion of Yth slows rehydration, directly linking bioenergetic processes to germination. Our data lead us to propose a powered germination model, where the Ger-mediated signalling cascade and bioenergetic processes occur simultaneously and semi-independently.

biophysics↗

bioRxiv2019

DNA origami nanostructures as a tool for the targeted destruction of bacteria

Antibiotic resistance is a growing worldwide human health issue that is now rendering us vulnerable once again to infections that have been treatable for decades. Various approaches have been proposed in an effort to overcome this threat and effectively treat bacterial infections. We use a DNA origami nanostructure, functionalized with aptamers, as a vehicle for delivering the antibacterial peptide lysozyme in a specific and efficient manner, in order to destroy bacterial targets. We test the system against Gram-positive (Bacillus subtilis) and Gram - negative (Escherichia coli) targets. We use direct stochastic optical reconstruction microscopy (dSTORM) and atomic force microscopy (AFM) to characterize the DNA origami nanostructures and structured illumination microscopy (SIM) to assess the binding of origami to the bacteria. We show that treatment with lysozyme-functionalized origami slows bacterial growth more effectively than treatment with free lysozyme. Our study introduces DNA origami as a tool in the fight against antibiotic resistance, and our results demonstrate the specificity and efficiency of the nanostructure as a drug delivery vehicle. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=105 SRC="FIGDIR/small/837252v2_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@1d7d8edorg.highwire.dtl.DTLVardef@1e2eb05org.highwire.dtl.DTLVardef@b3c671org.highwire.dtl.DTLVardef@a93a9e_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioengineering↗