Shane Gonen

Many symbioses exist along a continuum from cooperation to conflict. Latent bacterial viruses known as prophages embody this duality. Acting as both partner and predator, they can enhance bacterial fitness while retaining the capacity to kill their hosts through lytic replication. Yet what determines the balance between cooperation and conflict in prophage-bacterium symbioses, and how these associations avoid collapse, remains poorly characterized. To identify mechanisms that stabilize prophag-bacterium partnerships, we used experimental evolution to perturb a natural association through repeated cycles of transmission and reinfection. This perturbation consistently selected mutant hosts lacking capsular polysaccharide production and exposed a hidden conflict that proved detrimental to both partners. During lytic outbreaks, host cells suffered lethal collateral prophage attack while dispersing virions became entrapped on neighboring cells and lysis debris, severely restricting transmission. Genetic and imaging-based studies revealed that capsular polysaccharides suppress these maladaptive interactions by limiting phage readsorption at the cell surface. We term this host-mediated safeguard the Hyperion effect, after the Greek Titan of light. Hyperion interactions enable phages to radiate outward from host populations, thereby averting collateral attack and promoting viral transmission. Our findings demonstrate that conflicts between prophages and their hosts can extend beyond individual cells to whole populations, with consequences that scale to shape patterns of prophage spread and microbial community assembly. More broadly, our work illustrates how mutually beneficial prophage-bacterium interactions can arise not only through cooperation, but also through the suppression of mutually detrimental conflicts.

Nitrogenase catalyses small-molecule activation, and has great relevance to agronomy, environment and energy. Understanding the assembly of the complex nitrogenase cofactor is a decades-long goal in the field, and structural insights into this process remain scarce. Here we report a cryogenic electron microscopy (cryo-EM) study of heterologously expressed NifEN, a key player converting the precursor (L-cluster) to a mature cofactor (M-cluster). Structural analyses of apo- and holo-NifEN demonstrate major conformational changes triggered by L-cluster incorporation. Further examinations of NifEN structures with inwardly and outwardly bound L-clusters, coupled with supporting mutational studies, AlphaFold 3 predictions and negative-stain EM analyses of NifEN complexed with upstream (NifB) and downstream (NifH) assembly partners, reveal a tunnel linking NifEN with NifB and NifH, with NifEN serving as a dynamic hub that coordinates L-cluster reception, maturation and delivery via conformation-gated metallocluster trafficking.

Pathogenic Bordetella bacteria use protein adhesins to infect the ciliated respiratory epithelia of vertebrate hosts. In this work, we show that the filamentous hemagglutinin FhaB adhesin of Bordetella carries a C-terminal microtubule-binding domain (FhaB-CT), which is translocated into host cells to promote colonization. FhaB-CT delivery is required to occupy a niche at the base of cilia in airway epithelia, and mutant bacteria lacking this domain are defective for nasal colonization. These observations suggest that FhaB-CT is transferred into motile respiratory cilia to interact with core axonemal microtubules. We propose that Bordetella adheres initially to the tips of cilia and then deploys multiple FhaB adhesins to migrate to the base of the cilia forest, where the bacteria resist removal by the mucociliary “escalator” that normally clears the respiratory tract of microbes.

Rhodopsin, the most intensively studied G protein–coupled receptor (GPCR), is activated by light-induced isomerization of its chromophore 11- cis -retinal. This study employed cryogenic electron microscopy (cryo-EM) to investigate rhodopsin structure using a megabody (Mb7) as a negative allosteric modulator. Three distinct cryo-EM structures were solved: ground-state rhodopsin, photoactivated rhodopsin, and apo-rhodopsin, all in complex with Mb7. Photoactivated rhodopsin and apo-rhodopsin, both in complex with Mb7, maintain a conformation remarkably similar to ground-state rhodopsin rather than adopting a Meta-II-like conformation. Structural elements, including the conserved residues of the NPxxY motif and the ionic lock, remain in positions corresponding to inactive rhodopsin. The megabody forms extensive interactions with rhodopsin’s extracellular loop 2, N terminus, and glycans. The findings demonstrate that Mb7 stabilizes photoactivated rhodopsin in a Meta-I-like conformation, preventing progression to the active Meta-II state through specific immobilization of the extracellular domain. This work establishes a foundation for cryo-EM-guided discovery of ligands modulating rhodopsin.

Stenotrophomonas maltophilia is an understudied, gram-negative, aerobic bacterium that is widespread in the environment and increasingly a cause of opportunistic infections. Treating S. maltophilia remains difficult, leading to an increase in disease severity and higher hospitalization rates in people with cystic fibrosis, cancer, and other immunocompromised health conditions. The lack of effective antibiotics has led to renewed interest in phage therapy; however, there remains a great need for well-characterized phages, especially against S. maltophilia . In response to an oncology patient with a sepsis infection, we collected 18 phages from Southern California wastewater influent that exhibit different plaque morphology against S. maltophilia host strain B28B. We hypothesized that, when combined into a cocktail, genetically diverse phages would give rise to distinct lytic infection kinetics that would enhance bacterial killing when compared to the individual phages alone. We identified three genetically distinct clusters of phages, and a representative from each group was further investigated and screened for potential therapeutic use. The results demonstrated that the three-phage cocktail significantly suppressed bacterial growth compared with individual phages when observed for 48 h. We also assessed the lytic impacts of our three-phage cocktail against a collection of 46 S . maltophilia strains to determine if a multi-phage cocktail has an expanded host range. Our phages remained strain-specific and infected >50% of tested strains. In six clinically relevant S. maltophilia strains, the multi-phage cocktail has enhanced suppression of bacterial growth. These findings suggest that specialized phage cocktails may be an effective avenue of treatment for recalcitrant S. maltophilia infections resistant to current antibiotics.

Voltage-gated sodium channels (Na_Vs) selectively permit diffusion of sodium ions across the cell membrane and, in excitable cells, are responsible for propagating action potentials. One of the nine human Na_V isoforms, Na_V1.8, is a promising target for analgesics, and selective inhibitors are of interest as therapeutics. One such inhibitor, the gating-modifier peptide Protoxin-I derived from tarantula venom, blocks channel opening by shifting the activation voltage threshold to more depolarized potentials, but the structural basis for this inhibition has not previously been determined. Using monolayer graphene grids, we report the cryogenic electron microscopy structures of full-length human apo-Na_V1.8 and the Protoxin-I-bound complex at 3.1 Å and 2.8 Å resolution, respectively. The apo structure shows an unexpected movement of the Domain I S4-S5 helix, and VSD_I was unresolvable. We find that Protoxin-I binds to and displaces the VSD_II S3-S4 linker, hindering translocation of the S4_II helix during activation.

Voltage-gated sodium channels (Na _V s) selectively permit diffusion of sodium ions across the cell membrane and, in excitable cells, are responsible for propagating action potentials. One of the nine human Na _V isoforms, Na _V 1.8, is a promising target for analgesics, and selective inhibitors are of interest as therapeutics. One such inhibitor, the gating-modifier peptide Protoxin-I derived from tarantula venom, blocks channel opening by shifting the activation voltage threshold to more depolarised potentials, but the structural basis for this inhibition has not previously been determined. Using monolayer graphene grids, we report the cryogenic electron microscopy structures of full-length human apo-Na _V 1.8 and the Protoxin-I-bound complex at 3.1 Å and 2.8 Å resolution, respectively. The apo structure shows an unexpected movement of the Domain I S4-S5 helix, and VSD _I was unresolvable. We find that Protoxin-I binds to and displaces the VSD _II S3-S4 linker, hindering translocation of the S4 _II helix during activation.

The δ‐conotoxins, a class of peptides produced in the venom of cone snails, are of interest due to their ability to inhibit the inactivation of voltage‐gated sodium channels causing paralysis and other neurological responses, but difficulties in their isolation and synthesis have made structural characterization challenging. Taking advantage of recent breakthroughs in computational algorithms for structure prediction that have made modeling especially useful when experimental data is sparse, this work uses both the deep‐learning‐based algorithm AlphaFold and comparative modeling method RosettaCM to model and analyze 18 previously uncharacterized δ‐conotoxins derived from piscivorous, vermivorous, and molluscivorous cone snails. The models provide useful insights into the structural aspects of these peptides and suggest features likely to be significant in influencing their binding and different pharmacological activities against their targets, with implications for drug development. Additionally, the described protocol provides a roadmap for the modeling of similar disulfide‐rich peptides by these complementary methods.

Bacterial viruses (known as “phages”) shape the ecology and evolution of microbial communities, making them promising targets for microbiome engineering. However, knowledge of phage biology is constrained because it remains difficult to study phage transmission dynamics within multi-member communities and living animal hosts. We therefore created “Phollow”: a live imaging-based approach for tracking phage replication and spread in situ with single-virion resolution. Combining Phollow with optically transparent zebrafish enabled us to directly visualize phage outbreaks within the vertebrate gut. We observed that virions can be rapidly taken up by intestinal tissues, including by enteroendocrine cells, and quickly disseminate to extraintestinal sites, including the liver and brain. Moreover, antibiotics trigger waves of interbacterial transmission leading to sudden shifts in spatial organization and composition of defined gut communities. Phollow ultimately empowers multiscale investigations connecting phage transmission to transkingdom interactions that have the potential to open new avenues for viral-based microbiome therapies.

The delta-conotoxins, a class of peptide produced in the venom of cone snails, are of interest due to their ability to inhibit the inactivation of voltage-gated sodium channels causing paralysis and other neurological responses, but difficulties in their isolation and synthesis have made structural characterization challenging. Taking advantage of recent breakthroughs in computational algorithms for structure prediction that have made modeling especially useful when experimental data is sparse, this work uses both the deep-learning based algorithm AlphaFold and comparative modeling method RosettaCM to model and analyze 18 previously uncharacterized delta-conotoxins derived from piscivorous, vermivorous, and molluscivorous cone snails. The models provide useful insights into structural aspects of these peptides and suggest features likely to be significant in influencing their binding and different pharmacological activities against their targets, with implications for drug development. Additionally, the described protocol provides a roadmap for the modeling of similar disulfide-rich peptides by these complementary methods.