Biology subjects

Rosazza, T.

Publications and source records attributed to Rosazza, T..

6 recordsLinked to original sources

bioRxiv2026

Microbial cross-feeding interactions reshape evolutionary trajectories of consumers by preserving motility.

Cross-feeding interactions, in which a producer species release by-products that serve as resources for a consumer species, play an important role in shaping microbial community diversity. Producers create opportunities for consumers by supplying high-energy resources that are often scarce in the environment. However, they also exert strong top-down effects by releasing metabolites in pulses and generating spatial gradients of resource availability. How these spatiotemporal constraints shape consumer evolution remains poorly understood. To address this question, we used a two-species cross-feeding system in which Acinetobacter johnsonii excretes benzoate (a by-product of benzyl alcohol oxidation) into the external environment where it is consumed by Pseudomonas putida. To assess how the origin of benzoate (externally supplied or produced by cross-feeding) shapes consumer evolution, we evolved P. putida for 200 generations in monoculture or in co-culture with A. johnsonii. Populations evolved in monoculture exhibited improved growth relative to the ancestor, whereas populations evolved under cross-feeding showed little to no growth improvement. Whole-genome sequencing revealed pervasive loss-of-function mutations in flagellar genes among populations evolved in monoculture, but not under cross-feeding conditions. High-throughput imaging assays showed that populations evolved under cross-feeding not only maintained but also enhanced functional motility. Competition experiments with single mutants revealed context-dependent fitness effects: loss-of-function mutations were highly beneficial when benzoate was externally supplied but deleterious when benzoate was supplied by A. johnsonii, highlighting the importance of motility in cross-feeding interactions. Together, our results show that resource origin fundamentally reshapes selective pressures and alters evolutionary outcomes in microbial communities. Significance StatementCross-feeding interactions are pervasive in microbial communities, often arising from metabolite leakage into the environment. Our study focused on understanding how cross-feeding interactions shape the evolution of populations that cross-feed on these resources. Using a highly trackable cross-feeding system and linking genotypic to phenotypic changes, we showed that cross-feeding interactions reshape the evolutionary trajectories of consumer species. Notably, selection acts on flagellar genes, but their effects on function depend on the origin of resources. When resources are externally supplied, selection favors loss of flagellar motility, whereas when resources are generated through cross-feeding, selection not only maintains functional motility but also enhance it. These findings highlight that navigating the environment is essential for exploiting high-energy resources generated through cross-feeding.

microbiology↗

bioRxiv2026

Unilateral cross-feeding constrains adaptive evolution, even in the producer without direct fitness effects.

Cross-feeding interactions are pervasive in microbial communities and profoundly shape community structure, stability, and function. While previous studies have explored how cross-feeding affects evolvability, this work has predominantly focused on bidirectional mutualistic interactions in engineered auxotrophic systems where both partners reciprocally exchange essential metabolites. However, most metabolic interactions in natural microbial communities are unidirectional, with organisms feeding on the metabolic waste products of other species. Our study addresses this gap by examining how a unidirectional cross-feeding interaction affects the evolutionary dynamics of both the producer (Acinetobacter johnsonii) and consumer (Pseudomonas putida) over 800 generations of experimental evolution. We found that co-culture constrained adaptive evolution in both species. Co-cultures exhibited lower {pi}N/{pi}S ratios (0.75 for P. putida; 1.04 for A. johnsonii) than monocultures (1.44 and 2.02, respectively) indicating stronger purifying selection against nonsynonymous mutations in the community context. Lineage tracking through whole genome sequencing of populations and clones revealed greater lineage diversity and complexity in monocultures, with more mutations showing significant parallelism across replicate populations. Additionally, P. putida evolved increased dependence on its partner; co-culture-evolved P. putida grew significantly worse than its ancestor when A. johnsonii was removed. These findings demonstrate that ecological interactions fundamentally reshape fitness landscapes and constrain adaptive evolution even when fitness benefits are unidirectional, with implications for understanding microbial community stability and predicting evolutionary dynamics in complex communities.

evolutionary biology↗

bioRxiv2023

Reciprocal sharing of two classes of public goods facilitates Bacillus subtilis biofilm formation

Extracellular proteases are a class of public good that support growth of Bacillus subtilis when nutrients are in a polymeric form. B. subtilis biofilm matrix molecules are another class of public good that are needed for biofilm formation and prone to exploitation. In this study, we investigated the role of extracellular proteases in B. subtilis biofilm formation and explored interactions between different public good producer strains across various conditions. We confirmed that extracellular proteases support biofilm formation even when glutamic acid provides a freely available nitrogen source. Removal of AprE from the NCIB 3610 secretome adversely affects colony biofilm architecture, while sole induction of WprA activity into an otherwise extracellular protease-free strain is sufficient to promote wrinkle development within the colony biofilm. We found that changing the nutrient source used to support growth affected B. subtilis biofilm structure, hydrophobicity, and architecture. We propose that the different phenotypes observed may be due to increased protease dependency for growth when a polymorphic protein presents the sole nitrogen source. We however cannot exclude that the phenotypic changes are due to alternative matrix molecules being made. Co-culture of biofilm matrix and extracellular protease mutants can rescue biofilm structure, yet reliance on extracellular proteases for growth influences population coexistence dynamics. Our findings highlight the intricate interplay between these two classes of public goods, providing insights into microbial social dynamics during biofilm formation across different ecological niches.

microbiology↗

bioRxiv2023

Extracellular proteases are an essential public good supporting Bacillus subtilis growth through exogenous protein degradation

Bacteria encounter polymeric nutrient sources that need to be processed to support growth. Bacillus subtilis is a bacterium known for its adaptability and resilience within the rhizosphere and broader soil environment. Here we explore the role that a suite of extracellular proteases plays in supporting growth of B. subtilis when an extracellular heterologous protein (BSA) provides an abundant, but polymeric, food source. We confirm the essential role of extracellular proteases in this context and note the influence of the polymeric nutrient concentration on the yield of growth, but not on the relative level of extracellular proteases. We demonstrate the collective action of the extracellular proteases in supporting B. subtilis growth and evidence their use as a shared public good. Furthermore, we show that B. subtilis is subjected to a public good dilemma, but only in the context of using a polymeric food source. Using mathematical simulations, we uncover that this dilemma is driven by the relative cost of producing the public good. Collectively, our findings reveal how B. subtilis can survive in environments that vary significantly in terms of immediate nutrient accessibility. This information should inform steps to improve its efficacy as a biofertilizer in agricultural settings.

microbiology↗

bioRxiv2020

Dynamic High-Content Imaging Reveals Surface Exposure Of Virulent Leishmania Amastigotes In Infected Macrophages Undergoing Pyroptosis

Leishmania spp are obligate intracellular parasites that infect vertebrate phagocytes, notably macrophages. We previously reported that Leishmania amazonensis (L. am) subvert the host cell pro-inflammatory response by dampening the macrophage NLRP3 inflammasome. No information is available on how Leishmania infection affects inflammatory cell death termed pyroptosis, known to limit microbial infection. Here, we provide first evidence that L. amazonensis-infected macrophages can undergo pyroptosis when subjected to pro-inflammatory stimuli. We analyzed the dynamics of the pyroptotic process and the fate of intracellular amastigotes at the single cell level using spinning disk confocal microscopy and high-content, real-time imaging. Bone marrow-derived macrophages (BMDMs) were infected with L. am amastigotes isolated from footpad lesions and sequentially treated with lipopolysaccharide (LPS) and adenosine triphosphate (ATP) for canonical NLRP3 inflammasome priming and activation. Real-time monitoring was performed for 240 min post ATP addition. Longitudinal analyses revealed distinct phases of the pyroptotic process, including rapid decay of the parasitophorous vacuole (PV) as monitored by the pH-sensitive lysotracker fluid phase marker, progressive decrease in macrophage viability as monitored by accumulation of the nuclear dye YO-PRO-1, followed by translocation of the luminal PV membrane to the cell surface observed for 40% of macrophages, resulting in the extracellular exposure of amastigotes that remained anchored to the PV membrane. Scanning and transmission electron microscopy analyses revealed a highly polarized orientation of parasites with exclusive exposure of the anterior pole toward the extracellular milieu, and an attachment site forming a potential biological junction between the parasite posterior pole and the PV membrane. We showed that the exposed parasites are resistant to the cytolytic host cell activities linked to pyroptosis and retain their full infectious potential in reinfection experiments using naive macrophages. Together these data uncover a novel Leishmania immune subversion strategy that may allow stealthy parasite dissemination via the uptake of pyroptotic host debris by uninfected phagocytes.

immunology↗

bioRxiv2019

Leishmania targets the macrophage epigenome and dampens the NF-κB/NLRP3- mediated inflammatory response

Aberrant macrophage activation during intracellular infection generates important immunopathologies that can cause severe human morbidity. A better understanding of microbial immune subversion strategies and macrophage phenotypic and functional responses is a prerequisite for the design of novel, host-directed intervention strategies. Here, we uncover a fine-tuned transcriptional response induced in primary macrophages infected by the human parasite Leishmania amazonensis that prevents NF-{kappa}B and NLRP3 inflammasome activation. This unusual subversion is characterized by respectively suppression and induction of activating and de-activating components of the NF-{kappa}B and NLRP3 pathways. This dichotomic modulation was associated with histone H3 hypoacetylation at promoters of NF-{kappa}B-related, pro-inflammatory genes. Our results reveal a novel Leishmania immune subversion strategy targeting host cell epigenetic regulation to modulate the macrophage phenotype. Modulation of the macrophage epigenetic landscape establishes conditions beneficial for intracellular parasite survival, and opens interesting new venues for host-directed, anti-microbial drug discovery.

cell biology↗