Biology subjects

Mondino, S.

Publications and source records attributed to Mondino, S..

6 recordsLinked to original sources

bioRxiv2026

Core-sheath coupling controls flagellar curvature and motility in Leptospira

Spirochete pathogens are among the most invasive bacteria known, causing syphilis, Lyme disease, and leptospirosis. Their tissue penetration depends on periplasmic flagellar filaments that, unlike other bacterial flagella, are encased in a spirochete-specific multi-protein sheath and deform the cell body into motile waves. How these filaments achieve the mechanical properties needed for invasive motility has remained unclear. Here we determine complete atomic structures of the Leptospira endoflagellar filament, revealing an elaborate sheath of 9 to 12 distinct asymmetrically arranged proteins. We show that the flagellin variant forming the filament core determines sheath composition, producing curvatures ranging from [~]3.5 {micro}m-1 to [~]5 {micro}m-1. The lower-curvature architecture, employed by pathogenic Leptospira interrogans, proves essential for motility in viscous environments and during infection. Thus, Leptospira achieves environment-specific motility through modular core-sheath coupling, linking atomic-scale structural plasticity to large-scale changes in swimming behaviour. Conservation of key sheath components suggests this mechanism may extend across spirochetes.

microbiology↗

bioRxiv2026

Bacterial targeting of host paraspeckles uncovers a new SFPQ-based regulation

Nuclear functions are key in protecting cells against infections, yet intracellular pathogens like Legionella pneumophila can exploit these mechanisms to survive. We characterized a L. pneumophila protein, LpDot1, which shares sequence similarity with the eukaryotic catalytic domain of the histone methyltransferase DOT1. Structure determination, together with biochemical and biophysical analyses, revealed that LpDot1 methylates non-histone nuclear proteins, notably the splicing factor proline-glutamine rich protein (SFPQ). Importantly, LpDot1 targets the previously uncharacterized K518, located on an important structural motif of SFPQ, therefore impairing its dimerization in vitro. During infection, L. pneumophila modulates SFPQ abundance and activities in a LpDot1-dependent manner, thereby hijacking paraspeckle organization and the host cell splicing machinery, leading to alternative splice variants of infection related genes such as NF-kB2 and CD45. To our knowledge, this is the first report of a bacterial effector directly modifying paraspeckle dynamics, providing new insight into previously uncharacterized eukaryotic regulatory pathways.

microbiology↗

bioRxiv2023

The unique Legionella longbeachae capsule favors intracellular replication and immune evasion

Legionella longbeachae and Legionella pneumophila cause Legionnaires disease despite species-specific differences in environmental niches, disease epidemiology, and genomic content. Here, we characterized a new L. longbeachae virulence factor, a capsule that is expressed in post-exponential growth phase as shown by electron microscopy. Analysis of the capsule composition via HLPC revealed the presence of a highly anionic polysaccharide absent in a capsule mutant. The capsule is crucial for replication and virulence in vivo in a mouse model of infection and in the natural host Acanthamoeba castellanii. It has anti-phagocytic function when encountering innate immune cells, it is involved in a low cytokine responses in mice and in human monocyte derived macrophages and helps to dampen the innate immune response. The L. longbeachae capsule is a novel virulence factor, unique among known Legionella species, that aids L. longbeachae to survive in specific niches and partly confers L. longbeachae its unique infection characteristics.

microbiology↗

bioRxiv2022

Legionella para-effectors target chromatin and promote bacterial replication

Legionella pneumophila replicates intracellularly by secreting effectors via a type IV secretion system. One of these effectors is a eukaryotic methyltransferase (RomA) that methylates K14 of histone H3 (H3K14me3) to counteract host immune responses. However, it is not known how L. pneumophila infection catalyses H3K14 methylation as this residue is usually acetylated. Here we show that L. pneumophila secretes a eukaryotic-like histone deacetylase (LphD) that specifically targets H3K14ac and works in synergy with RomA. Both effectors target host chromatin and bind the HBO1 histone acetyltransferase complex that acetylates H3K14. Full activity of RomA is dependent on the presence of LphD as H3K14 methylation levels are significantly decreased in a {Delta}lphD mutant. The dependency of these two chromatin-modifying effectors on each other is further substantiated by mutational and virulence assays revealing that the presence of only one of these two effectors impairs intracellular replication, while a double knockout ({Delta}lphD{Delta}romA) can restore intracellular replication. Uniquely, we present evidence for "para-effectors", an effector pair, that actively and coordinately modify host histones to hijack the host response. The identification of epigenetic marks modulated by pathogens opens new vistas for the development of innovative therapeutic strategies to counteract bacterial infection and strengthening host defences.

microbiology↗

bioRxiv2020

FasR regulates fatty acid biosynthesis and is essential for virulence of Mycobacterium tuberculosis

Mycobacterium tuberculosis, the etiologic agent of human tuberculosis, is the worlds leading cause of death from an infectious disease. One of the main features of this pathogen is the complex and dynamic lipid composition of the cell envelope, which adapts to the variable host environment and defines the fate of infection by actively interacting with and modulating immune responses. However, while much has been learned about the enzymes of the numerous lipid pathways, little knowledge is available regarding the proteins and metabolic signals regulating lipid metabolism during M. tuberculosis infection. In this work, we constructed and characterized a FasR-deficient mutant in M. tuberculosis and demonstrated that FasR positively regulates fas and acpS expression. Lipidomic analysis of the wild type and mutant strains revealed complete rearrangement of most lipid components of the cell envelope, with phospholipids, mycolic acids, sulfolipids and phthiocerol dimycocerosates relative abundance severely altered. As a consequence, replication of the mutant strain was impaired in macrophages leading to reduced virulence in a mouse model of infection. Moreover, we show that the fasR mutant resides in acidified cellular compartments, suggesting that the lipid perturbation caused by the mutation prevented M. tuberculosis inhibition of phagolysosome maturation. This study identified FasR as a novel factor involved in regulation of mycobacterial virulence and provides evidence for the essential role that modulation of lipid homeostasis plays in the outcome of M. tuberculosis infection.

microbiology↗

bioRxiv2018

More than 16,000 effectors in the Legionella genus genome provide multiple, independent combinations for replication in human cells

SignificanceLegionella pneumophila is a bacterial pathogen causing outbreaks of a lethal pneumonia. The genus Legionella comprises 65 species for which aquatic amoebae are the natural reservoirs. Using functional and comparative genomics to deconstruct the entire bacterial genus we reveal the surprising parallel evolutionary trajectories that have led to the emergence of human pathogenic Legionella. An unexpectedly large and unique repository of secreted proteins (>16,000) containing eukaryotic-like proteins acquired from all domains of life (plant, animal, fungal, archaea) is contrasting with a highly conserved type 4 secretion system. This study reveals an unprecedented environmental reservoir of bacterial virulence factors, and provides a new understanding of how reshuffling and gene-acquisition from environmental eukaryotic hosts, may allow for the emergence of human pathogens.\n\nAbstractThe bacterial genus Legionella comprises 65 species among, which Legionella pneumophila is a human pathogen causing severe pneumonia. To understand the evolution of an environmental to an accidental human pathogen, we have functionally analyzed 80 Legionella genomes spanning 58 species. Uniquely, an immense repository of 16,000 secreted proteins encoding 137 different eukaryotic-like domains and more than 200 eukaryotic-like proteins is paired with a highly conserved T4SS. Specifically, we show that eukaryotic Rho and Rab GTPase domains are found nearly exclusively in eukaryotes and Legionella species. Translocation assays for selected Rab-GTPase proteins revealed that they are indeed T4SS secreted substrates. Furthermore, F/U-box and SET domains were present in >70% of all species suggesting that manipulation of host signal transduction, protein turnover and chromatin modification pathways, respectively are fundamental intracellular replication strategies for Legionellae. In contrast, the Sec-7 domain was restricted to L. pneumophila and seven other species, indicating effector repertoire tailoring within different amoebae. Functional screening of 47 species revealed 60% were competent for intracellular replication in THP-1 cells, but interestingly this phenotype was associated with diverse effector assemblages. These data, combined with evolutionary analysis indicate that the capacity to infect eukaryotic cells has been acquired independently many times within the genus and that a highly conserved yet versatile T4SS secretes an exceptional number of different proteins shaped by inter-domain gene transfer. Furthermore we revealed the surprising extent to which legionellae have co-opted genes and thus cellular functions from their eukaryotic hosts and provides a new understanding of how dynamic reshuffling and gene-acquisition has led to the emergence of major human pathogens.

genomics↗