Biology subjects

Limoli, D. H.

Publications and source records attributed to Limoli, D. H..

6 recordsLinked to original sources

bioRxiv2025

Pseudomonas aeruginosa phenazines dictate site-specific competitive interactions with Klebsiella pneumoniae

Pseudomonas aeruginosa and Klebsiella pneumoniae are Gram-negative opportunistic pathogens that frequently colonize the human body and are major causes of infection. These bacteria are often co-isolated in polymicrobial urinary tract and lung infections, the latter of which is associated with increased disease severity and worse clinical outcomes. Despite their overlapping niches and clinical relevance, little is known about how these two pathogens interact and how those interactions influence human health. Given the growing recognition that microbial interactions are key drivers of disease, we investigated how P. aeruginosa and K. pneumoniae influence one another. We discovered an antagonistic interaction in which P. aeruginosa restricts the growth of K. pneumoniae. This inhibition is driven by phenazine production in P. aeruginosa, specifically the secondary metabolites pyocyanin and pyorubin, which are both necessary and sufficient to suppress K. pneumoniae growth. Using a diverse set of clinical isolates, we found that this antagonism is strain dependent. Both the susceptibility of K. pneumoniae to phenazines and the ability of P. aeruginosa to restrict K. pneumoniae growth varies between strains. Moreover, the necessity of phenazine production is specific to the site of infection. Together, these findings demonstrate that strain background and environmental context are critical determinants of pathogen interactions. Our work underscores the importance of considering these variables when investigating how microbial interactions influence infection and disease outcomes.

microbiology↗

bioRxiv2024

Pseudomonas aeruginosa surface motility and invasion into competing communities enhances interspecies antagonism

Chronic polymicrobial infections involving Pseudomonas aeruginosa and Staphylococcus aureus are prevalent, difficult to eradicate, and associated with poor health outcomes. Therefore, understanding interactions between these pathogens is important to inform improved treatment development. We previously demonstrated that P. aeruginosa is attracted to S. aureus using type IV pili-mediated chemotaxis, but the impact of attraction on S. aureus growth and physiology remained unknown. Using live single-cell confocal imaging to visualize microcolony structure, spatial organization, and survival of S. aureus during coculture, we found that interspecies chemotaxis provides P. aeruginosa a competitive advantage by promoting invasion into and disruption of S. aureus microcolonies. This behavior renders S. aureus susceptible to P. aeruginosa antimicrobials. Conversely, in the absence of type IV pilus motility, P. aeruginosa cells exhibit reduced invasion of S. aureus colonies. Instead, P. aeruginosa builds a cellular barrier adjacent to S. aureus and secretes diffusible, bacteriostatic antimicrobials like 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO) into the S. aureus colonies. P. aeruginosa reduced invasion leads to the formation of denser and thicker S. aureus colonies with significantly increased HQNO-mediated lactic acid fermentation, a physiological change that could complicate the effective treatment of infections. Finally, we show that P. aeruginosa motility modifications of spatial structure enhance competition against S. aureus. Overall, these studies build on our understanding of how P. aeruginosa type IV pili-mediated interspecies chemotaxis mediates polymicrobial interactions, highlighting the importance of spatial positioning in mixed-species communities.

microbiology↗

bioRxiv2023

The great divide: rhamnolipids mediate separation between P. aeruginosa and S. aureus

The coexistence of multiple bacterial species during infection can have significant impacts on pathogenesis. Pseudomonas aeruginosa and Staphylococcus aureus are opportunistic bacterial pathogens that can co-infect hosts and cause serious illness. The factors that dictate whether one species will outcompete the other or whether the two species can coexist are not fully understood. We investigated the role of surfactants in the interactions between these two species on a surface that enables P. aeruginosa to swarm. We found that P. aeruginosa swarms are repelled by colonies of clinical S. aureus isolates, creating physical separation between the two strains. This effect was abolished in mutants of S. aureus that were defective in the production of phenol-soluble modulins (PSMs), which form amyloid fibrils around wild-type colonies. We investigated the mechanism that establishes physical separation between the two species using the Imaging of Reflected Illuminated Structures (IRIS) method, which tracks the flow of the rhamnolipid surfactant layer produced by P. aeruginosa. We found that PSMs produced by S. aureus deflected the rhamnolipid surfactant layer flow, which in turn, altered the direction of P. aeruginosa swarms. These findings show that rhamnolipids mediate physical separation between P. aeruginosa and S. aureus, which enables these species to coexist in distinct microenvironments. Additionally, we found that a Bacillus subtilis surfactant and abiotic hydrophobic molecules repelled P. aeruginosa swarms through surfactant deflection. Our results suggest that surfactant interactions could have major impacts on bacteria-bacteria and bacteria-host relationships. In addition, our findings uncover a mechanism responsible for P. aeruginosa swarm development that does not rely on sensing but instead is guided largely by the flow of the surfactant layer and its boundaries.

microbiology↗

bioRxiv2023

Staphylococcal secreted cytotoxins are competition sensing signals for Pseudomonas aeruginosa

Coinfection with two notorious opportunistic pathogens, the Gram-negative Pseudomonas aeruginosa and Gram-positive Staphylococcus aureus, dominates chronic pulmonary infections. While coinfection is associated with poor patient outcomes, the interspecies interactions responsible for such decline remain unknown. Here, we dissected molecular mechanisms of interspecies sensing between P. aeruginosa and S. aureus. We discovered that P. aeruginosa senses S. aureus secreted peptides and, counterintuitively, moves towards these toxins. P. aeruginosa tolerates such a strategy through "competition sensing", whereby it preempts imminent danger/competition by arming cells with type six secretion (T6S) and iron acquisition systems. Intriguingly, while T6S is predominantly described as weaponry targeting Gram-negative and eukaryotic cells, we find that T6S is essential for full P. aeruginosa competition with S. aureus, a previously undescribed role for T6S. Importantly, competition sensing was activated during coinfection of bronchial epithelia, including T6S islands targeting human cells. This study reveals critical insight into both interspecies competition and how antagonism may cause collateral damage to the host environment.

microbiology↗

bioRxiv2022

Twitching cells use a chemoreceptor to detect bacterial competitors

Bacteria live in cosmopolitan communities, where the ability to sense and respond to interspecies and environmental signals is critical for survival. We previously showed the pathogen Pseudomonas aeruginosa detects secreted peptides from bacterial competitors and navigates interspecies signal gradients using pilus-based motility. Yet, it remained unknown whether P. aeruginosa utilizes a designated chemosensory system for this behavior. Here, we performed a comprehensive genetic analysis of a putative pilus chemosensory system to reveal behaviors of mutants that retain motility, but are blind to interspecies signals. The enzymes predicted to methylate (PilK) and demethylate (ChpB) the putative pilus chemoreceptor, PilJ, are necessary for cells to control the direction of migration. While these findings implicate PilJ as a bona fide chemoreceptor, such function had yet to be experimentally defined, as PilJ is essential for motility. Thus, we constructed systematic genetic modifications of PilJ and found that without the predicted ligand binding domains or methylation sites cells lose the ability to detect competitor gradients, despite retaining pilus-mediated motility. Collectively, this work uncovers the chemosensory nature of PilJ, providing insight into chemotactic interactions necessary for bacterial survival in polymicrobial communities and revealing putative pathways where therapeutic intervention might disrupt bacterial communication.

microbiology↗

bioRxiv2019

Interspecies signaling generates exploratory motility in Pseudomonas aeruginosa

Microbes often live in multispecies communities where interactions among community members impact both the individual constituents and the surrounding environment. Here, we developed a system to visualize interspecies behaviors at initial encounters. By imaging two prevalent pathogens known to be coisolated from chronic illnesses, Pseudomonas aeruginosa and Staphylococcus aureus, we observed P. aeruginosa can modify surface motility in response to secreted factors from S. aureus. Upon sensing S. aureus, P. aeruginosa transitioned from collective to single-cell motility with an associated increase in speed and directedness - a behavior we refer to as exploratory motility. Through modulation of cAMP, explorer cells moved preferentially towards S. aureus and invaded S. aureus colonies through the action of the type IV pili. These studies reveal previously undescribed motility behaviors and lend insight into how P. aeruginosa senses and responds to other species. Identifying strategies to harness these interactions may open avenues for new antimicrobial strategies.

microbiology↗