Biology subjects

Alvarado, G.

Publications and source records attributed to Alvarado, G..

8 recordsLinked to original sources

bioRxiv2026

Salmonella sensitizes macrophages for context-dependent anti-inflammatory response

Macrophages critical role in the innate immune response depends on their ability to change their activation state in response to environmental signals, generating cells with diverse functions ranging from antimicrobial activity to tissue repair. However, this plasticity in activation state represents a vulnerability that intracellular pathogens have evolved to exploit. Salmonella Typhimurium (STm) harnesses macrophage plasticity to promote anti-inflammatory states conducive to bacterial survival and replication. Although this anti-inflammatory state is well-characterized, how it is established remains unclear. Using smFISH, we find that STm is a weak pro-inflammatory trigger and fails to directly induce anti-inflammatory polarization. Instead, we show that STm creates a sensitized cell state with enhanced responsiveness to the cytokine IL-4. While we found that IL-4R[a] upregulation is a common feature of infected cells, the sensitized state is independent of receptor upregulation. Polarization resulting from this sensitized state is context-dependent, with bacterial load and effector secretion distinctly amplifying expression of the anti-inflammatory genes, Il4ra and Arg1. Together, our results establish a two-signal model in which pathogen-driven sensitization and environmental IL-4 combine to drive macrophage anti-inflammatory polarization.

systems biology↗

bioRxiv2025

Microbiome Dynamics During Translocation of the Critically-Endangered Frog Craugastor ranoides

O_LIAmphibian populations are declining and species going extinct due to habitat loss, climate change and emerging infectious disease, prompting the increasing use of translocations as a conservation tool. C_LIO_LISkin-associated microbial communities play a key role in amphibian health, particularly in protecting hosts from pathogenic infection. However, to date we know relatively little about the impact of translocation on the dynamics of skin-associated microbes, or the consequences of translocation-mediated disturbance of the microbiome for amphibian health. C_LIO_LIWe investigated the skin microbiome of the critically endangered frog Craugastor ranoides, now restricted to a fraction of its historical range in Costa Rica. We first conducted a multi-population survey to characterise among-population variation in skin bacterial communities. We then translocated individuals to a new site, using radio tracking to monitor them over time and assess individual-level changes in body mass, microbiome composition, and predicted microbial function. C_LIO_LIWe found limited among-population variation in skin microbiome composition across three different populations of C. ranoides. Response of the microbiome to translocation was highly individual-specific; some frogs demonstrated relatively stable community richness and composition, whilst others exhibited marked turnover in bacterial membership and predicted function. Body mass showed similar dynamics, but several of the recaptured frogs had gained mass after several days in the translocation site. C_LIO_LISynthesis and Applications: Our findings highlight the importance of considering microbiome dynamics in threatened species translocations to optimize individual health. This includes considering whether individuals should be prioritised for translocation based on their initial microbiome composition, and understanding how shifts in microbiome post-translocation may alter overall success of translocation efforts. These insights extend beyond amphibians, offering a broader framework for integrating long-term monitoring of host microbiomes and health into conservation efforts. C_LI

ecology↗

bioRxiv2024

Growth of Staphylococcus aureus in the presence of oleic acid shifts the glycolipid fatty acid profile and increases resistance to antimicrobial peptides

Staphylococcus aureus readily adapts to various environments and quickly develops antibiotic resistance, which has led to an increase in multidrug-resistant infections. Hence, S. aureus presents a significant global health issue and its adaptations to the host environment are crucial for understanding pathogenesis and antibiotic susceptibility. When S. aureus is grown conventionally, its membrane lipids contain a mix of branched-chain and straight-chain saturated fatty acids. However, when unsaturated fatty acids are present in the growth medium, they become a major part of the total fatty acid composition. This study explores the biophysical effects of incorporating straight-chain unsaturated fatty acids into S. aureus membrane lipids. Membrane preparations from cultures supplemented with oleic acid showed more complex differential scanning calorimetry scans than those grown in tryptic soy broth alone. When grown in the presence of oleic acid, the cultures exhibited a transition significantly above the growth temperature, attributed to the presence of glycolipids with long-chain fatty acids causing acyl chain packing frustration within the bilayer. Functional aspects of the membrane were assessed by studying the kinetics of dye release from unilamellar vesicles induced by the antimicrobial peptide mastoparan X. Dye release was slower from liposomes prepared from cells grown in oleic acid-supplemented cultures, suggesting that changes in membrane lipid composition and biophysics protect the cell membrane against peptide-induced lysis. These findings underscore the intricate relationship between the growth environment, membrane lipid composition, and the physical properties of the bacterial membrane, which should be considered when developing new strategies against S. aureus infections.

biophysics↗

bioRxiv2024

Lipidomics of homeoviscous adaptation to low temperatures in Staphylococcus aureus utilizing exogenous straight-chain unsaturated fatty acids over biosynthesized endogenous branched-chain fatty acids

It is well established that Staphylococcus aureus can incorporate exogenous straight-chain unsaturated fatty acids (SCUFAs) into membrane phospho- and glyco-lipids from various sources in supplemented culture media, and when growing in vivo in an infection. Given the enhancement of membrane fluidity when oleic acid (C18:1{Delta}9) is incorporated into lipids, we were prompted to examine the effect of medium supplementation with C18:1{Delta}9 on growth at low temperatures. C18:1{Delta}9 supported the growth of a cold-sensitive, branched-chain fatty acid (BCFA)-deficient mutant at 12{degrees}C. Interestingly, we found similar results in the BCFA-sufficient parental strain. We show that incorporation of C18:1{Delta}9 and its elongation product C20:1{Delta}9 into membrane lipids was required for growth stimulation and relied on a functional FakAB incorporation system. Lipidomics analysis of the phosphatidylglycerol (PG) and diglycosyldiacylglycerol (DGDG) lipid classes revealed major impacts of C18:1{Delta}9 and temperature on lipid species. Growth at 12{degrees}C in the presence of C18:1{Delta}9 also led to increased production of the carotenoid pigment staphyloxanthin; however, this was not an obligatory requirement for cold adaptation. Enhancement of growth by C18:1{Delta}9 is an example of homeoviscous adaptation to low temperatures utilizing an exogenous fatty acid. This may be significant in the growth of S. aureus at low temperatures in foods that commonly contain C18:1{Delta}9 and other SCUFAs in various forms. IMPORTANCEWe show that S. aureus can use its known ability to incorporate exogenous fatty acids to enhance its growth at low temperatures. Individual species of phosphatidylglycerols and diglycosyldiacylglycerol bearing one or two degrees of unsaturation derived from incorporation of C18:1{Delta}9 at 12{degrees}C are described for the first time. In addition, enhanced production of the carotenoid staphyloxanthin occurs at low temperatures. The studies describe a biochemical reality underlying in membrane biophysics. This is an example of homeoviscous adaptation to low temperatures utilizing exogenous fatty acids over the regulation of the biosynthesis of endogenous fatty acids. The studies have likely relevance to food safety in that unsaturated fatty acids may enhance growth of S. aureus in the food environment.

microbiology↗

bioRxiv2021

The Human STAT2 Coiled-Coil Domain Contains a Degron for Zika Virus Interferon Evasion

The ability of viruses to evade the host antiviral immune system determines their level of replication fitness, species specificity, and pathogenic potential. Flaviviruses rely on the subversion of innate immune barriers including the type I and type III IFN antiviral systems. Zika virus infection induces the degradation of STAT2, an essential component of the IFN stimulated gene transcription factor, ISGF3. The mechanisms that lead to STAT2 degradation by Zika virus are poorly understood, but it is known to be mediated by the viral NS5 protein that binds to STAT2 and targets it for proteasome-mediated destruction. To better understand how NS5 engages and degrades STAT2, functional analysis of the protein interactions that lead to Zika virus and NS5-dependent STAT2 proteolysis were investigated. Data implicate the STAT2 coiled-coil domain as necessary and sufficient for NS5 interaction and proteasome degradation after Zika virus infection. Molecular dissection reveals that the first two -helices of the STAT2 coiled-coil contain a specific targeting region for IFN antagonism. These functional interactions provide a more complete understanding of the essential protein-protein interactions needed for Zika virus evasion of the host antiviral response, and identifies new targets for antiviral therapeutic approaches. ImportanceZika virus infection can cause mild fever, rash, and muscle pain, and in rare cases lead to brain or nervous system diseases including Guillain-Barre syndrome. Infections in pregnant women can increase the risk of miscarriage or serious birth defects including brain anomalies and microcephaly. There are no drugs or vaccines for Zika disease. Zika virus is known to break down the host antiviral immune response, and this research project reveals how the virus suppresses interferon signaling, and may reveal therapeutic vulnerabilities.

microbiology↗

bioRxiv2020

Lipidomic and Ultrastructural Characterization of Cell Envelope of Staphylococcus aureus Grown in the Presence of Human Serum

Staphylococcus aureus can incorporate exogenous straight-chain unsaturated and saturated fatty acids (SCUFAs and SCFAs, respectively) to replace some of the normally biosynthesized branched-chain fatty acids and SCFAs. In this study, the impact of human serum on the S. aureus lipidome and cell envelope structure was comprehensively characterized. When grown in the presence of 20% human serum, typical human serum lipids, such as cholesterol, sphingomyelin, phosphatidylethanolamines, and phosphatidylcholines, were present in the total lipid extracts. Mass spectrometry showed that SCUFAs were incorporated into all major S. aureus lipid classes, i.e., phosphatidylglycerols, lysyl-phosphatidylglycerols, cardiolipins, and diglucosyldiacylglycerols. Heat-killed S. aureus retained much fewer serum lipids and failed to incorporate SCUFAs, suggesting that association and incorporation of serum lipids with S. aureus requires a living or non-denatured cell. Cytoplasmic membranes isolated from lysostaphin-produced protoplasts of serum-grown cells retained serum lipids, but washing cells with Triton X-100 removed most of them. Furthermore, electron microscopy studies showed that serum-grown cells had thicker cell envelopes and associated material on the surface, which was partially removed by Triton X-100 washing. To investigate which serum lipids were preferentially hydrolyzed by S. aureus lipases for incorporation, we incubated individual serum lipid classes with S. aureus and found that cholesteryl esters (CEs) and triglycerides (TGs) are the major donors of the incorporated fatty acids. Further experiments using purified Geh lipase confirmed CEs and TGs being the substrates of this enzyme. Thus, growth in the presence of serum altered the nature of the cell surface with implications for interactions with the host. IMPORTANCEComprehensive lipidomics of S. aureus grown in the presence of human serum suggests human serum lipids can associate with the cell envelope without being truly integrated into the lipid membrane. However, fatty acids-derived from human serum lipids, including unsaturated fatty acids, can be incorporated into lipid classes that can be biosynthesized by S. aureus itself. Cholesteryl esters and triglycerides are found to be the major source of incorporated fatty acids upon hydrolysis by lipases. These findings have significant implications for the nature of the S. aureus cell surface when grown in vivo. Changes in phospholipid and glycolipid abundances and fatty acid composition could affect membrane biophysics and function and the activity of membrane-targeting antimicrobials. Finally, the association of serum lipids with the cell envelope has implications for the physicochemical nature of the cell surface and its interaction with host defense systems.

microbiology↗

bioRxiv2018

Prevalence of the fungal pathogen Batrachochytrium dendrobatidis in amphibians of Costa Rica predated first-known epizootic

Emerging infectious diseases are a growing threat to biodiversity worldwide. Outbreaks of the infectious disease chytridiomycosis, caused by the fungal pathogen Batrachochytrium dendrobatidis (Bd), have caused the decline and extinction of numerous amphibian species. In Costa Rica, a major decline event occurred in 1987, more than two decades before this pathogen was discovered. The loss of many species in Costa Rica is assumed to be due to Bd-epizootics, but there are few studies that provide data from amphibians in the time leading up to the proposed epizootics. In this study, we provide new data on Bd infection rates of amphibians collected throughout Costa Rica, in the decades prior to the epizootics. We used a quantitative PCR assay to test for Bd infection in 1016 specimens collected throughout Costa Rica. We found Bd-infected hosts collected as early as 1964, and a infection prevalence average per decade of just 4%. The infection prevalence remained relatively low and geographically constrained until the 1980s when epizootics are hypothesized to have occurred. After that time, infection prevalence increased three-fold and Bd-infected hosts we collected throughout the entire country. Our results, suggest that Bd may either have invaded Costa Rica earlier than previously known, and spread more slowly than previously reported, or that an endemic lineage of the pathogen may exists. To help visualize areas where future studies should take place, we provide a Bd habitat suitability model trained with local data. Studies that provide information on genetic lineages of Bd are needed to determine whether an endemic lineage of Bd or the Global Panzootic Lineage (identified from mass die off sites globally) was present in Costa Rica and responsible for the epizootics that caused amphibian communities to collapse.

ecology↗

bioRxiv2018

Bioinformatic analysis reveals mechanisms underlying parasitoid venom evolution and function

Introduction Introduction Methods Results and Discussion Conclusions References Parasitoid wasps are a numerous and diverse group of insects that obligately infect other arthropod species. These wasps lay their eggs either on the surface or within the body cavity of their hosts, and the resulting offspring exploit the hosts resources to complete their development [1]. Many parasitoids also introduce venom gland derived proteins or polydnaviruses into the host during infection. These factors act through a variety of mechanisms to manipulate host biology in order to increase the fitness of the developing parasitoid offspring [2-4]. Many hosts mount immune responses to parasitoid infection, and accordingly, parasitoids have evolved multiple venom genes that encode immunom ...

genomics↗