Biology subjects

Pimenta, A. I.

Publications and source records attributed to Pimenta, A. I..

3 recordsLinked to original sources

bioRxiv2026

Structural basis of sulfide production in dissimilatory sulfur metabolism

The membrane-bound DsrMK(JOP) complex is central to dissimilatory sulfur metabolism, including in sulfate-reducing microbes (SRM), a group that plays important roles in shaping planetary and human health. Despite this global importance, the mechanism of sulfide production and its links to energy conservation remain unclear. Here, we present high-resolution cryo-EM structures of DsrMKJOP from Archaeoglobus fulgidus, alone, with menadiol and with the sulfur-carrying substrate DsrC-trisulfide, complemented by physiological and biochemical studies. The results clarify how SRM control the reactivity of sulfur to selectively achieve sulfide production. While DsrC-trisulfide is highly stable in isolation, interaction with the DsrK subunit facilitates its hydrolytic activation, triggering a conformational change. This brings a perthiosulfenate sulfur intermediate into the catalytic pocket of DsrK for reduction at a single non-cubane [4Fe-4S] cluster, likely supported by a conserved non-ligating cysteine. DsrM harbors a structural quinone-binding site, but seems not to catalyze menaquinol oxidation, although this likely occurs in DsrMK complexes from different sulfur-metabolizing organisms. In DsrMKJOP, trisulfide reduction by DsrK is linked to quinol oxidation at DsrP, releasing protons to the periplasm to generate a proton-motive force.

microbiology↗

bioRxiv2026

Virulence studies of the human gut pathobiont Bilophila wadsworthia using Galleria mellonella as model host

Bilophila wadsworthia is a gut pathobiont implicated in dysbiosis-driven inflammation, yet its pathogenic mechanisms remain poorly investigated. Here, we evaluated the suitability of Galleria mellonella larvae as an in vivo model to study B. wadsworthia infection. Two infection routes were compared: oral inoculation to mimic gastrointestinal colonization and hemolymph injection to model systemic infection. Oral challenge had minimal impact on larval health, whereas hemolymph injection caused marked morbidity, including reduced mobility, impaired cocoon formation, and progressive melanization, indicating that access to the circulatory system is required for overt disease. Infection required live bacteria, with B. wadsworthia capable of intracellular replication within hemocytes, leading to transient depletion of circulating immune cells followed by compensatory hemocyte proliferation. These findings reveal tight coupling between bacterial proliferation and host immune dynamics. Comparison with other sulfidogenic bacteria suggests that Bilophila pathogenicity is likely to involve host-specific interactions. Overall, our results establish G. mellonella as a practical and ethically favorable model to investigate B. wadsworthia virulence, host-pathogen interactions, and mechanisms relevant to gut-associated infection.

microbiology↗

bioRxiv2023

Role of the inner membrane cytochrome ImcH in Geobacter extracellular electron transfer and energy conservation

Electroactive bacteria combine the oxidation of carbon substrates with an extracellular electron transfer (EET) process that discharges electrons to an electron acceptor outside the cell. This process involves electron transfer through consecutive redox proteins that efficiently connect the inner membrane to the cell exterior. In this study, we isolated and characterized the quinone-interacting membrane cytochrome c ImcH from Geobacter sulfurreducens, which is involved in the EET process to high redox potential acceptors. Our work provides evidence that ImcH is electroneutral, as it transfers electrons and protons to the same side of the membrane, contributing to the maintenance of a proton motive force, and plays a central role in recycling the menaquinone pool. ImportanceGeobacter sulfurreducens is a model electroactive bacterium, widespread in the environment and of significant interest for biotechnological applications. Its ability to form thick and conductive biofilms on top of conducting surfaces makes this microbe very useful in bioelectrochemical systems for the production of energy or added value products. To explore Geobacter spp. as a biocatalyst it is essential to understand its metabolism, particularly the molecular mechanisms for extracellular electron transfer and energy conservation. Our results reveal the importance of ImcH in both processes, identifying this protein as a major player on Geobacter metabolism.

biochemistry↗