Biology subjects

Cavallaro, A.

Publications and source records attributed to Cavallaro, A..

8 recordsLinked to original sources

bioRxiv2026

Siderophore-mediated inhibition of Legionella pneumophila by environmental Pseudomonas isolates

The genus Legionella comprises opportunistic pathogenic bacteria commonly found in natural and engineered water systems, where they interact with environmental microbes and protozoa, primarily in biofilms. Legionella pneumophila is the main causative agent of Legionnaires disease and is transmitted through inhalation of contaminated aerosols. Iron availability is a critical factor for L. pneumophila growth, persistence, and virulence, yet iron is often limited in aquatic environments. To overcome iron scarcity, many bacteria produce siderophores, secondary metabolites that scavenge ferric iron. Because siderophores are chemically diverse and species specific, they play a key role in inter-species competition and can withhold iron from competitors. Here, we investigated the effects of iron depletion and siderophore-mediated competition on L. pneumophila using commercial pyoverdines and extracellular metabolites from environmental Pseudomonas strains. Growth assays showed that L. pneumophila can grow under iron-limited conditions but with lag phases extended by more than 20 hours. Pyoverdines inhibited growth in a concentration-dependent manner, primarily increasing the time to mid-log phase (t_mid). Supernatants and crude pyoverdine extracts from siderophore-producing Pseudomonas strains caused the strongest inhibition, including lag-phase extensions of up to 55 hours or complete growth arrest. These results demonstrate that siderophore-producing bacteria can suppress L. pneumophila by limiting iron availability.

microbiology↗

bioRxiv2025

Phage-mediated lysis increases growth rate of surviving bacterial cells

Bacterial phage infection and subsequent lysis are traditionally considered mechanisms of bacterial mortality and viral propagation; additionally, emerging evidence indicates that they may also contribute to nutrient recycling in broader ecological systems. However, it remains unclear how the nutrients released during cell lysis affect the growth dynamics of the remaining bacterial population. Addressing this gap, we built a controlled system consisting of two Escherichia coli lysogenic strains: one carrying a wild-type{lambda} prophage and the other a temperature-inducible variant that can be induced to lyse at 38 {degrees}C. Using this system, we selectively induced phage lysis in a defined fraction of the population and quantified both total biomass and the biomass of surviving, non-lysed cells. We observed that the biomass loss was consistently smaller than expected based on the fraction of lysed cells, supporting the idea that some of the released biomass is rapidly recycled by the non-lysed population. To formalize the observed dynamics and obtain quantitative insight, we developed a mathematical model showing that nutrients released during lysis can transiently enhance the growth rate of the surviving, non-lysed cells. This effect emerges on a short timescale of minutes, consistent with the rapid onset of biomass compensation observed experimentally. The growth rate increase was confirmed in single-cell experiments using microfluidics and time-lapse microscopy, where we cultured wild-type lysogens in lysate-containing culture supernatants. In summary, the results suggest that nutrients released through lysis are rapidly consumed, leading to an acceleration in the growth rate of non-lysed cells. The consequent partial compensation for cell loss can substantially influence the population dynamics, highlighting phage lysis as a direct modulator of bacterial growth. Overall, our findings provide quantitative insights into how phage-mediated lysis affects the physiology of non-lysed bacterial cells, extending beyond its well-established role in biomass recycling.

microbiology↗

bioRxiv2024

Variable inhibition of different Legionella species by antagonistic bacteria

The genus Legionella includes opportunistic pathogens inhabiting engineered aquatic ecosystems, where managing their presence and abundance is crucial for public health. In these environments, Legionella interact positively or negatively with multiple members of the microbial communities. Here, we identified bacteria and compounds with Legionella-antagonistic properties. We isolated 212 bacterial colonies from various water sources in Switzerland and screened them for their ability to inhibit one reference strain of L. pneumophila. Ten selected antagonistic isolates were subsequently tested with spot-on-lawn-assays for inhibition towards seven environmental and two clinical isolates of Legionella, representing different species and strains. The antagonists produced highly variable inhibition patterns, highlighting distinct differences in susceptibility among Legionella species, and even strains. Only three isolates, all identified as Pseudomonas lurida, inhibited all Legionella species. Furthermore, we analysed the genomes of the antagonistic bacteria, and identified genes for several probable inhibitory compounds. We specifically found the gene cluster for the biosurfactant viscosin to be uniquely encoded by three Pseudomonas lurida isolates. This compound was subsequently detected in the supernatant of co-cultures inoculated with the antagonists and Legionella. This study provides new insights on the ability of aquatic microorganisms to compete with Legionella in controlled laboratory settings. It also highlights the diversity across and within Legionella species in their resistance to external antagonistic stress, and confirms the anti-Legionella activity of selected biosurfactants. These results can contribute to the understanding of how different species inhabit separate niches in the environment, and expand the discussion around alternative Legionella mitigation strategies.

microbiology↗

bioRxiv2024

Expansion, restructuring and characterization of the Legionellaceae family

Legionellaceae is a large and widespread family of facultative intracellular bacteria with high clinical relevance. While Legionella pneumophila, the most clinically relevant species, is relatively well studied, very limited information is available regarding the other species belonging to this family, despite its only recognized genus (i.e., Legionella) being included in water regulations worldwide. Here, we analyzed publicly-available Legionellaceae isolates and metagenome-assembled genomes, nearly doubling the number of recognized species and highlighting the need to consider restructuring the familys taxonomy to include multiple genera that present distinct clinical relevance. We further found that, except for Type II and IVB secretion systems, traits linked to host invasion vary significantly across species, likely influencing their host range and survival in the environment. Presumptive genus clusters exhibited variations in metabolic capabilities, but L. pneumophila and closely related species generally displayed more complete pathways and fewer auxotrophies, suggesting a less strict intracellular lifestyle. On the contrary, specific deep-branching clades show reduced genome size and the lack of poly-3-hydroxybutyrate biosynthetic potential suggesting a stronger host association. Finally, we showed that most species are present across various environments and that, while they have apparently distinct environmental distributions, niche overlap increases at higher metabolic similarity. Together, our results shed light on the ecology of these microorganisms, highlight the diversity of traits that can occur in closely related facultative intracellular bacteria, and call for the restructuring of this family to align with genomic information and clinical relevance to aid the management of Legionellaceae bacteria. ImportanceSpecies belonging to the Legionellaceae family are responsible for Legionnaires disease, the leading waterborne disease in many industrialized countries. Historically, the focus was (and still is) on Legionella pneumophila, and the ecology of other species remained largely unknown and unexplored. However, several water safety regulations cover the entire Legionella genus,currently the only recognized within this large family, thus including species with unknown health relevance and ecology. This work provides an in-depth characterization of the genomic diversity across the family Legionellaceae, highlighting the concentration of clinically-relevant species in specific clades presenting distinct putative phenotypes linked to host invasion, metabolism and environmental niches. These findings highlight the need to consider restructuring the taxonomy of the family Legionellaceae in multiple genera to prioritize interventions to control the presence of the most clinically-relevant ones and advance public health protection.

microbiology↗

bioRxiv2024

The impact of DNA extraction on the quantification of Legionella, with implications for ecological studies

Monitoring the levels of opportunistic pathogens in drinking water is important to plan interventions and understand the ecological niches that allow them to proliferate. Quantitative PCR is an established alternative to culture methods that can provide a faster, higher throughput, and more precise enumeration of the bacteria in water samples. However, PCR-based methods are still not routinely applied for Legionella monitoring, and techniques such as DNA extraction differ notably between laboratories. Here, we quantify the impact that DNA extraction methods had on downstream PCR quantification and community sequencing. Through a community science campaign, we collected 50 water samples and corresponding shower hoses, and compared two commonly used DNA extraction methodologies to the same biofilm and water phase samples. The two methods showed clearly different extraction efficacies, which was reflected in both the quantity of DNA extracted and the concentrations of Legionella enumerated in both the matrices. Notably, one method resulted in higher enumeration in nearly all samples by about one order of magnitude and detected Legionella in 21 samples that remained undetected by the other method. 16S rRNA amplicon sequencing revealed that the relative abundance of individual taxa, including sequence variants of Legionella, significantly varied depending on the extraction method employed. Given the implications of these findings, we advocate for improvement in documentation of the performance of DNA extraction methods used in drinking water to detect and quantify Legionella, and characterise the associated microbial community.

microbiology↗

bioRxiv2024

A split-GAL4 driver line resource for Drosophila CNS cell types

Techniques that enable precise manipulations of subsets of neurons in the fly central nervous system have greatly facilitated our understanding of the neural basis of behavior. Split-GAL4 driver lines allow specific targeting of cell types in Drosophila melanogaster and other species. We describe here a collection of 3060 lines targeting a range of cell types in the adult Drosophila central nervous system and 1373 lines characterized in third-instar larvae. These tools enable functional, transcriptomic, and proteomic studies based on precise anatomical targeting. NeuronBridge and other search tools relate light microscopy images of these split-GAL4 lines to connectomes reconstructed from electron microscopy images. The collections are the result of screening over 77,000 split hemidriver combinations. Previously published and new lines are included, all validated for driver expression and curated for optimal cell type specificity across diverse cell types. In addition to images and fly stocks for these well-characterized lines, we make available 300,000 new 3D images of other split-GAL4 lines.

neuroscience↗

bioRxiv2023

Legionella relative abundance in shower hose biofilms is associated with specific microbiome members

Legionella are natural inhabitants of building plumbing biofilms, where interactions with other microorganisms influence their survival, proliferation, and death. Here, we investigated the associations of Legionella with prokaryotic and eukaryotic microbiomes in biofilm samples extracted from 85 shower hoses of a multiunit residential building. Legionella spp. relative abundance in the biofilms ranged between 0 - 7.8%, of which only 0 - 0.46% was L. pneumophila. Our data suggest that some microbiome members were associated with high (e.g., Chthonomonas, Vrihiamoeba) or low (e.g., Aquabacterium, Vannella) Legionella relative abundance. The correlations of the different Legionella variants (30 Zero-Radius OTUs detected) showed distinct patterns, suggesting separate ecological niches occupied by different Legionella species. This study provides insights into the ecology of Legionella with respect to: 1) the colonization of a high number of real shower hoses biofilm samples; 2) the ecological meaning of associations between Legionella and co-occurring prokaryotic/eukaryotic organisms; 3) critical points and future directions of microbial-interaction-based-ecological-investigations.

microbiology↗

bioRxiv2017

Genetic reagents for making split-GAL4 lines in Drosophila

The ability to reproducibly target expression of transgenes to small, defined subsets of cells is a key experimental tool for understanding many biological processes. The Drosophila nervous system contains thousands of distinct cell types and it has generally not been possible to limit expression to one or a few cell types when using a single segment of genomic DNA as an enhancer to drive expression. Intersectional methods, in which expression of the transgene only occurs where two different enhancers overlap in their expression patterns, can be used to achieve the desired specificity. This report describes a set of over 2,800 transgenic lines for use with the split-GAL4 intersectional method.

neuroscience↗