Biology subjects

Perez, F.

Publications and source records attributed to Perez, F..

At least 19 recordsLinked to original sources

bioRxiv2026

Senescence targeting re-enables injury-responsive repair in a human RPE aging model

Aging is associated with progressive tissue dysfunction and impaired repair after injury. In the retinal pigment epithelium (RPE), these changes contribute to age-related macular degeneration (AMD), yet the mechanisms limiting repair remain incompletely understood. Here, we establish a longitudinal human embryonic stem cell (hESC)-derived RPE aging model that recapitulates key features of aged human donor RPE and combine it with mosaic cell ablation to assess injury-responsive repair. Although aged RPE cells initiate DNA synthesis after injury, they exhibit impaired mitotic progression, uncoupling S-phase entry from epithelial repopulation. Transcriptomic profiling links this defect to a senescence-associated program marked by inflammatory signaling and suppressed mitotic networks. Pharmacologic reduction of senescent cells with Navitoclax shifts aged RPE toward a younger transcriptional profile but does not induce repopulation by itself. Instead, senolytic treatment primes aged RPE for repair, improving epithelial density and homeostatic function only in response to injury, a strategy we term "senolytic priming." These findings establish a human stem-cell-derived platform for investigating age-associated epithelial repair failure and show that aged human RPE retains latent repair capacity that can be re-enabled by targeting cellular senescence.

Cell Biology↗

bioRxiv2026

Non-covalent reversibly photoconvertible fluorescent tags for wash-free protein labeling

Reversibly photoswitchable fluorophores are widely used in advanced bioimaging but their design remains demanding. Here, we introduce a new series spanning the whole visible range, which results from combining a large set of fluorogens with the FAST protein scaffold. We first demonstrate that these well-established labeling fluorescent protein tags turn into negative reversible photoswitchers upon decreasing the fluorogen concentration and increasing light intensity. We then show that using not anymore one but two fluorogens adds new responses to illumination. Thus, we obtain positive reversible photoswitchers, that increase their brightness under illumination. We also generate a palette of non-covalent reversibly photoconvertible fluorescent proteins changing their fluorescence color upon illumination, a reversible behavior that still remains absent in regular fluorescent proteins. This light-induced color change opens the possibility to discriminate six spectrally similar FAST variants in live cells upon demonstrating the superiority of using multiple spectral channels for exploiting the time dependence of the fluorescence response to illumination.

biophysics↗

bioRxiv2025

Photoejection turns non-covalent fluorescent tags into negative reversible photoswitchers

Reversibly photoswitchable fluorophores have enabled a broad range of applications in advanced fluorescence bioimaging. Here, we introduce RSpFAST, a new class of reversibly photoswitchable fluorescent labels that combine a biomolecular host (pFAST protein tag) with a reversibly photoisomerizable guest (fluorogen), allowing fluorescence brightness to be modulated through illumination and molecular complexation. We combine thermokinetic, photochemical, and structural investigations to obtain a comprehensive mechanistic and kinetic understanding of RSpFAST. Building on this theoretical framework, we demonstrate in both live and fixed cells that RSpFAST exhibits an unprecedented dual behavior: a stable and wash-free fluorescent labeling tag turns into a negative reversible photoswitcher by lowering the fluorogen concentration and increasing light intensity. In this photoejection-driven kinetic regime, RSpFAST is shown to be an efficient marker for dynamic contrast and super-resolution microscopy.

biochemistry↗

bioRxiv2025

Hot and Bothered, Bees Gut Microbiome Shifts Under Thermal Stress and Pathogen Infection.

Understanding bumble bee gut health is imperative as these vital pollinators are subjected to pathogenic infections and thermal stress from climate change. The gut microbiome serves as an indicator for health and fitness and indicates the types of stress. To investigate the combined effects of thermal stress and pathogenic infection on bee guts, we performed a two-by-two crossed design where Bombus impatiens workers were subjected to hot conditions, pathogenic infection, or both. Incubation groups were given 2-weeks of stress conditions, with infected bees initially inoculated with Crithidia bombi, a common bee gut parasite. We measured body size, quantified the infection intensity of C. bombi using qPCR, and defined the composition of the gut microbiome using full-length 16S rRNA gene amplicon sequencing on an Oxford Nanopore Technologies Mk1D. While the core gut microbiome thrived with genera such as Bombilactobacillus and Snodgrassila which were not impacted by treatment; there were notable changes in other key organisms. Asaia bogorensis spiked in control temperature infected organisms, while species of Lactobacillus were overtaken in hot temperatures by significant increases in Apilactobacillus kunkeei. Species such as Citrobacter freundii dominated in hot infected bees suggesting an increased immunocompromised state from the combined stressors impacts on bee gut health. Our novel combined effects from thermal stress and pathogenic infection strengthen existing literature and provide new directions on how to quantify the health-state of wild bees based on their gut microbiome composition. These insights enable us to better understand how bees will be further impacted in changing landscapes. ImportanceWe find significant changes in bees gut microbiome especially with an increased abundance of lactic acid bacteria. These lactic acid bacteria are often specialized: based on infection status, temperature, and the combined effects. These insights are vital to researchers, especially those studying wild bee gut health where they have an uncontrolled system and need to make assumptions about bee stress based on fitness and microbiome. Our detailed outline of relevant species will provide wild bee researchers with a baseline to determine thermal stress and recent infection status based on microbiome communities. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=111 SRC="FIGDIR/small/687019v1_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@1528ae6org.highwire.dtl.DTLVardef@1d100dorg.highwire.dtl.DTLVardef@8ea77org.highwire.dtl.DTLVardef@159620a_HPS_FORMAT_FIGEXP M_FIG C_FIG Overview of the experimental design where bees were either given control temperatures or thermal stress and/or an infection by Crithidia bombi. The bees microcolonies were incubated for 2-weeks before sacrificing the bees, extracting DNA, and performing downstream analysis. Full length 16S rRNA gene amplicon sequencing was performed on an Oxford Nanopore MK1D sequencer while Crithidia bombi infections were quantified using quantitative polymerase chain reaction.

ecology↗

bioRxiv2025

De novo Golgi biogenesis requires coordinated transactivation of a Golgi regulon

The Golgi apparatus expands during differentiation and high secretory demand, yet the transcriptional control of its biogenesis remains poorly defined. Here, we developed a targeted enzymatic ablation method to eliminate the Golgi and trigger de novo organelle formation. Single-cell RNA-seq of cells rebuilding Golgi revealed an orchestrated induction of a broad Golgi gene network coinciding with structural and functional organelle maturation. This gene set spans all Golgi sub-compartments and functions, including glycosylation, trafficking, and ion transport, thus supporting the concept of a unified Golgi regulon, enabling the simultaneous expression of components required for the organelle structural and functional integrity. Through promoter analysis and RNAi screening, we identified CREB3L1 as a key transcriptional regulator critical for Golgi gene activation and organelle reformation. These findings indicate that CREB3L1-dependent transcriptional mechanisms orchestrate a complete Golgi biogenesis program that may be essential for organelle regeneration and for secretory pathway plasticity during physiological remodeling.

cell biology↗

bioRxiv2025

Mechanical forces stimulate Golgi export

Cells face diverse mechanical stimuli that vary with cell type, state, and pathological conditions. Mechanobiology investigates how cells sense and respond to these forces. While most work has focused on the cell surface and nucleus as primary mechanosensors, how intracellular organelles adapt to extracellular mechanical forces remains largely unknown. Here, we show that extracellular mechanical signals influence the secretory function of the Golgi apparatus. By subjecting adherent cells to mechanical challenges -cell spreading on different ligands, altered substrate stiffness, or equibiaxial strain-, we reveal that extracellular forces modulate Golgi-to-cell surface carrier biogenesis, thereby regulating exocytosis. Together with changes in Golgi membrane tension, we identify molecular determinants of the mechanotransduction pathway, including microtubule acetylation, diacylglycerol production, and protein kinase D activity. In turn, inhibition of Golgi export suppresses this mechanoresponse and causes impaired cell spreading. These findings uncover a bidirectional mechanotransduction axis in which extracellular mechanics tune Golgi secretory output, providing a framework for investigating organelle-based mechanoadaptation in physiology and disease.

cell biology↗

bioRxiv2025

Chemically responsive protein switches for the precise control of biological activities

Controlling the proximity or interaction of proteins with small molecules enables researchers to chemically regulate cellular functions. Here, we leveraged CATCHFIRE (chemically assisted tethering of chimera by fluorogenic induced recognition) - a technology enabling to chemically induce dimerization in a reversible manner - to create chemically responsive proteins switches for the precise and reversible control of various biological activities. CATCHFIRE allowed us to chemically induce the assembly and thus function of various split enzymes - including luciferases, proteases, DNA recombinases. We extended this approach to develop CATCH-ON, a chemically inducible gene expression system relying on the chemically induced dimerization of the DNA-binding domain GAL4 and the truncated transcription factor p65{Delta}. CATCH-ON allowed us to precisely regulate the expression of cellular enzymes such as proteases, DNA recombinases, or suicide switches, as well as to control the secretion of therapeutically relevant proteins such as insulin. We showed that the CATCH-ON system is fast-acting, reversible, titratable, non-toxic and compatible with other chemically induced dimerization systems, opening exciting possibilities for its application in basic research, biotechnology and cell therapy.

bioengineering↗

bioRxiv2025

The magnitude of cryptic insect diversity in one tropical rainforest

O_LICryptic species represent significant entities in conservation planning and are common among tropical insects. Many studies focusing on cryptic species have been restricted to a narrow taxon and it is not clear whether some insect clades or assemblages may have a greater propensity for cryptic speciation than others. Here, we contrast cryptic diversity among 22 insect assemblages surveyed on Barro Colorado Island (BCI), a tropical rainforest in Panama. C_LIO_LICryptic species were defined as externally indistinguishable from their sister species but with a different barcode index number. We detected 214 cryptic species out of a total of 2,006 species studied (10.6%). The percentage of cryptic species varied greatly among assemblages (0-19%), with half of assemblages devoid of cryptic species, and the highest proportions of cryptics in Pieridae and Formicidae. C_LIO_LIThe percentage of cryptic species was weakly influenced by phylogeny and it was best explained by the local number of species and an index of taxonomic knowledge. Cryptic species were distinguished by an average distance divergence in sequence of 9%, but their ecological characteristics remain unclear. C_LIO_LIAsymptotic estimates indicated that 11.4% of species studied on BCI may be cryptic. Since many of the species-rich insect assemblages occurring on BCI were not considered in this study, this estimate probably represents a lower bound to the true cryptic insect richness on BCI. C_LIO_LIThis significant contribution to biodiversity should not be ignored and, because of apparent low population levels, may be particularly vulnerable to land use and climate changes. C_LI

evolutionary biology↗

bioRxiv2024

Identification of an Outbreak of Bivalve Transmissible Neoplasia in Soft-Shell Clams (Mya arenaria) in the Puget Sound Using Hemolymph and eDNA Surveys

Bivalve transmissible neoplasia (BTN) is one of three known types of naturally transmissible cancer-- cancers in which the whole cancer cells move from individual to individual, spreading through natural populations. BTN is a lethal leukemia-like cancer that has been observed throughout soft-shell clam (Mya arenaria) populations on the east coast of North America, with two distinct sublineages circulating at low enzootic levels in New England, USA, and Prince Edward Island, Canada. Major cancer outbreaks likely due to Mya arenaria BTN (MarBTN) were reported in 1980s and the 2000s and the disease has been observed since the 1970s, but it has not been observed in populations of this clam species on the US west coast. In 2022, we collected soft-shell clams from several sites in Puget Sound, Washington, USA, and unexpectedly found high prevalence of BTN in two sites (Triangle Cove on Camano Island and near Stanwood in South Skagit Bay). Prevalence of BTN increased in subsequent years, reaching >75% in both sites in 2024, while it was not observed in other sites, suggesting the early stages of a severe disease outbreak following recent introduction. We observed that these cancer cells contain several somatic transposing insertion sites found only in the USA-sublineage of MarBTN, showing that it likely was recently transplanted from New England to this location. We then developed a sensitive environmental DNA (eDNA) assay, using qPCR to target somatic mutations in the MarBTN mitogenome, and showed that MarBTN can be detected in seawater at Triangle Cove, as well as several kilometers outside of the cove. We then used this assay to survey 50 sites throughout Puget Sound, confirming that the disease can be detected at high levels at Triangle Cove and South Skagit Bay, and showing that it extends beyond these known sites. However, while normal soft-shell clam mtDNA was widely detected, MarBTN was undetectable throughout most of Puget Sound and currently remains limited to the South Skagit Bay area and north Port Susan. These results identify a previously unknown severe outbreak of a transmissible cancer due to long-distance transplantation of disease from another ocean, and they demonstrate the utility of eDNA methods to track the spread of BTN through the environment.

ecology↗

bioRxiv2024

Optimization of the VSV G backbone for amino terminal fusion with nanobodies allowing its retargeting to receptors of therapeutic interest.

Vesicular stomatitis virus (VSV) is a promising oncolytic virus. Additionally, its glycoprotein G is the most commonly used envelope glycoprotein to pseudotype lentiviral vectors for gene therapy. However, G receptors (LDLR family members) are ubiquitous and expressed at the surface of non-target cells, precluding in vivo gene therapy. Recently, we identified G mutants that no longer bind to LDLR but retain their fusion activity. This opened the possibility of specifically retargeting the glycoprotein to receptors of interest. Here, we constructed chimeric glycoproteins fused with a nanobody at the amino-terminus of G. By experimental evolution, we identified two mutations in G improving the folding and functionality of chimeric Gs, regardless of the nanobody inserted at the amino-terminus. We then constructed chimeric glycoproteins using several nanobodies targeting HER2 receptor and, into these chimeras, we introduced mutations that abolish the recognition of LDL receptors. VSV and lentiviruses pseudotyped with these glycoproteins specifically infect cells expressing HER2. We have therefore identified G mutations that optimize the G scaffold to tolerate amino-terminal insertion of a nanobody and establish proof of concept that this approach can be used to confer a new tropism on G. This paves the way for targeted in vivo therapies.

bioengineering↗

bioRxiv2024

A tunable and versatile chemogenetic near infrared fluorescent reporter

Near-infrared (NIR) fluorescent reporters provide additional colors for highly multiplexed imaging of cells and organisms, and enable imaging with less toxic light and higher contrast and depth. Here, we present the engineering of nirFAST, a small tunable chemogenetic NIR fluorescent reporter that is brighter than top-performing NIR fluorescent proteins in cultured mammalian cells. nirFAST is a small genetically encoded protein of 14 kDa that binds and stabilizes the fluorescent state of synthetic, highly cell-permeant, fluorogenic chromophores (so-called fluorogens) that are otherwise dark when free. Engineered to emit NIR light, nirFAST can also emit far-red or red lights through change of chromophore. nirFAST allows the imaging of proteins in live cultured mammalian cells, chicken embryo tissues and zebrafish larvae. Its near infrared fluorescence provides an additional color for high spectral multiplexing. We showed that nirFAST is well-suited for stimulated emission depletion (STED) nanoscopy, allowing the efficient imaging of proteins with subdiffraction resolution in live cells. nirFAST enabled the design of a chemogenetic green-NIR fluorescent ubiquitination-based cell cycle indicator (FUCCI) for the monitoring of the different phases of the cell cycle. Finally, bisection of nirFAST allowed the design of a fluorogenic chemically induced dimerization technology with NIR fluorescence readout, enabling the control and visualization of protein proximity.

cell biology↗

bioRxiv2023

Single-cell spatial atlas of tertiary lymphoid structures in ovarian cancer

BackgroundRecent advances in highly-multiplexed tissue technologies and image analysis tools have enabled a more detailed investigation of the tumor microenvironment (TME) and its spatial features, including tertiary lymphoid structures (TLSs), at single-cell resolution. TLSs play a major part in antitumor immune responses, however, their role in antitumor immunity in ovarian cancer remains largely unexplored. MethodsIn this study, we generated a comprehensive single-cell spatial atlas of TLSs in ovarian cancer by extracting spatial topology information from in-situ highly-multiplexed cellular imaging using tissue cyclic immunofluorescence (CyCIF). Our analysis included 44 patients with high-grade serous ovarian cancer (HGSC) from the TOPACIO Phase II clinical trial. We combined spatial and phenotypic features from 302,545 single-cells with histopathology, targeted sequencing-based tumor molecular groups, and Nanostring gene expression data. ResultsWe find that TLSs are associated with a distinct TME composition and gene expression profile, characterized by elevated levels of the chemokines CCL19, CCL21, and CXCL13 correlating with the number of TLSs in the tumors. Using single-cell feature quantification and spatial mapping, we uncover enriched germinal center (GC) B cell infiltration and selective spatial attraction to follicular helper T and follicular regulatory T cells in the TLSs from chemo-exposed and BRCA1 mutated HGSCs. Importantly, spatial statistics reveal three main groups of cell-to-cell interactions; significantly enriched structural compartments of CD31+ cells, myeloid, and stromal cell types, homotypic cancer cell- and cancer cell to IBA1+ myeloid cell crosstalk, and enriched selective Tfh, Tfr, and Tfc communities with predominant Tfh - GC B cell interactions. Finally, we report spatiotemporal gradients of GC-B cell interactions during TLS maturation, with enriched non-GC B cell attraction towards the GC B cells in early TLSs, and avoidance patterns with selective GC B-cell communities in the TLSs with GCs. ConclusionsOur single-cell multi-omics analyses of TLSs showed evidence of active adaptive immunity with spatial and phenotypic variations among distinct clinical and molecular subtypes of HGSC. Overall, our findings provide new insights into the spatial biology of TLSs and have the potential to improve immunotherapeutic targeting of ovarian cancer. What is already known on this topicTLSs play a major part in antitumor immune responses, however, their exact role and mechanisms in antitumor immunity are widely unexplored. What this study addsOur results deepen the understanding of TLS biology including cell-cell interactions and shows how the presence of TLSs is characterized with a distinct TME composition and gene expression profile. How this study might affect research, practice or policyOverall, our findings provide new insights into the spatial biology of TLSs and have the potential to improve therapeutic options for ovarian cancer.

cancer biology↗

bioRxiv2023

Phase partitioning initiates Rab protein membrane domain formation and promote vesicle tethering

Diverse cellular processes are regulated by the formation of specific membrane domains displaying specific lipid and protein compositions. Liquid-liquid phase separation (LLPS) recently emerged as one possible mechanism for their biogenesis, but the examples remain scarce and the impact of LLPS properties on this process is not well established. Rab GTPases are present on all intracellular membranes and play a crucial role in membrane identity, trafficking and compartmentalization. Domain formation is thought to play a central role in Rab functions. Here we show that several Rab partners with common structural characteristics present LLPS properties, some being able to co-condensate or on the contrary presenting immiscible properties. These properties limit the recruitment of Rabs to the membrane sub-domains defined by the condensates of their specific partners. We further show that those LLPS properties control the recruitment of Rab5 to Rabaptin5 condensates ensuring Rab5 functions in regulating endocytic vesicle tethering and fusion. We propose a universal mechanism for Rab domain formation, delimitation, growth and docking based on LLPS properties of Rab partners.

cell biology↗

bioRxiv2023

A phosphorylation switch regulates RAB6 function during mitosis

RAB GTPases are key regulators of membrane trafficking in eukaryotic cells. In addition to their role in interphase, several RAB proteins, including Golgi-associated RAB6, have mitotic functions. The aim of this study was to investigate how the interphasic and mitotic functions of RAB6 could be regulated. Since phosphorylation is a key regulatory process in mitosis, we looked for specific mitotic phosphorylation of RAB6 using a phospho-proteomic approach. We found that RAB6 is phosphorylated at position S52 by the mitotic kinase Pololike kinase 1 (Plk1) in mitosis. Phosphorylated RAB6 localizes at the spindle poles from prophase to anaphase. In metaphase, we observed RAB6A-positive structures containing Mad1 and Mad2 moving along the mitotic spindle via the dynein-dynactin complex. We provide evidence that phosphorylation impairs RAB6A binding to some of its known partners, including p150Glued and Bicaudal-D2. In addition, the overexpression of RAB6A phospho-mutants lead to mitosis and cytokinesis defects. Our results suggest that a cycle of RAB6 phosphorylation/dephosphorylation is required for cell division.

cell biology↗

bioRxiv2023

A fluorogenic chemically induced dimerization technology for controlling, imaging and sensing protein proximity

Proximity between proteins plays an essential and ubiquitous role in many biological processes. Molecular tools enabling to control and observe the proximity of proteins are essential for studying the functional role of physical distance between two proteins. Here we present CATCHFIRE (Chemically Assisted Tethering of CHimera by Fluorogenic Induced REcognition), a chemically induced proximity technology with intrinsic fluorescence imaging and sensing capabilities. CATCHFIRE relies on genetic fusion to small dimerizing domains that interact upon addition of fluorogenic inducers of proximity that fluoresce upon formation of the ternary assembly, allowing real-time monitoring of the chemically induced proximity. CATCHFIRE is rapid and fully reversible, and allows the control and tracking of protein localization, protein trafficking, organelle transport and cellular processes, opening new avenues for studying or controlling biological processes with high spatiotemporal resolution. Its fluorogenic nature allowed furthermore the design of innovative biosensors for the study of various processes, such as signal transduction and apoptosis.

cell biology↗

bioRxiv2022

Regulation of cell dynamics by rapid transport of integrins through the biosynthetic pathway

Cells sense and respond to the extracellular matrix (ECM) milieu through integrin proteins. Integrin availability on the plasma membrane, regulated by endosomal receptor uptake and recycling, has been extensively studied and regulates cell dynamics in various normal and pathological contexts1-5. In contrast, the role of integrin transport through the biosynthetic pathway has been considered primarily as a mechanism to replenish the receptor pool and too slow to influence cell dynamics6. Here, we adopted the RUSH (Retention Using Selective Hooks) assay to synchronize integrin anterograde transport from the endoplasmic reticulum (ER), allowing spatial and temporal analysis of newly synthesized receptor traffic. We observe that the delivery of new integrins to the plasma membrane is polarized in response to specific ECM ligands, facilitates integrin recruitment specifically to the membrane-proximal tip of focal adhesions (FA) and contributes to cell protrusion and FA growth. We explain the augmented adhesion growth using a computational molecular clutch model7, where increased integrin availability drives recruitment of additional integrins. Notably, a subset of newly synthesized integrins undergo rapid traffic from the ER to the cell surface to facilitate localized cell spreading, seemingly bypassing the Golgi. This unconventional secretion is dependent on cell adhesion and mediated by Golgi reassembling stacking proteins (GRASPs) association with the PDZ-binding motif in the integrin 5 cytoplasmic tail. This spatially targeted delivery of integrins through the biosynthetic pathway may propel cell dynamics by rapidly altering adhesion receptor availability, providing cells with an additional degree of plasticity to respond to their environment.

cell biology↗

bioRxiv2021

Regulation of neuronal progenitor delamination by dynein-driven post-Golgi apical transport

Radial glial (RG) cells are the neural stem cells of the developing neocortex. Apical RG (aRG) cells can delaminate to generate basal RG (bRG) cells, a cell type associated with human brain expansion. Here, we report that this delamination is regulated by the post-Golgi secretory pathway. Using in situ subcellular live imaging, we show that post-Golgi transport of RAB6+ vesicles occurs toward the minus ends of microtubules and depends on dynein. We demonstrate that the apical determinant Crumbs3 (CRB3) is also transported by dynein. Double knockout of RAB6A/A and RAB6B impairs apical localization of CRB3, and induces a retraction of aRG cell apical process, leading to delamination and ectopic division. These defects are phenocopied by knock-out of the dynein activator LIS1. Overall, our results identify a RAB6-dynein-LIS1 complex for Golgi to apical surface transport in aRG cells, and highlights the role of this pathway in the maintenance of neuroepithelial integrity.

cell biology↗

bioRxiv2021

Interplay between meropenem and human serum albumin on expression of carbapenem resistance genes and natural competence in Acinetobacter baumannii

Acinetobacter baumannii A118, a mostly susceptible strain, and AB5075, carbapenem-resistant, were cultured in L broth or L broth with different supplements: 3.5% human serum albumin (HSA), human serum (HS), meropenem, or meropenem plus 3.5% HSA. Natural transformation levels were enhanced in A. baumannii A118 and AB5075 cultured in medium supplemented with 3.5 % HSA. Addition of meropenem plus 3.5% HSA caused synergistic enhancement of natural transformation in A. baumannii A118. Medium containing 3.5% HSA or meropenem enhanced the expression levels of the competence and type IV pilus associated genes. The combination meropenem plus 3.5% HSA produced a synergistic augmentation in the expression levels of many of these genes. The addition of HS, which has a high content of HSA, was also an inducer of these genes. Cultures in medium supplemented with HS or 3.5% HSA also affected resistance genes, which were expressed at higher or lower levels depending on the modification required to enhance resistance. The inducing or repressing activity of these modulators also occurred in three more carbapenem-resistant strains tested. An exception was the A. baumannii AMA16 blaNDM-1 gene, which was repressed in the presence of 3.5% HSA. In conclusion, HSA produces an enhancement of natural transformation and a modification in expression levels of competence genes and antibiotic resistance. Furthermore, when HSA is combined with carbapenems, which may produce stronger cellular stress, the A. baumannii responds increasing the levels of expression of genes involved in natural competence. This process may favor the acquisition of foreign DNA and accelerate evolution. ImportanceAcinetobacter baumannii causes a variety of nosocomial- and community-infections that are usually resistant to multiple antimicrobial agents. As new strains acquire more resistance genes, these infections become harder to treat, and mortality can reach up to 39%. The high genomic plasticity exhibited by A. baumannii must be the consequence of numerous mechanisms that include acquiring foreign DNA and recombination. Here, we describe the ability of A. baumannii to induce competence genes when exposed to environments that resemble those found in the human body during untreated infection or after administration of carbapenems. In this latter scenario expression of genes related to resistance also modify their expression levels such that resistance is increased. The contributions of this article are two-pronged. First, when A. baumannii is exposed to substances present during infection, it responds, augmenting the ability to capture DNA and accelerate evolution. Second, in those conditions, the bacterium also modifies the expression of resistance genes to increase its resistance levels. In summary, recognition of substances that are naturally (HSA) or artificially (treatment with carbapenems) induces A. baumannii to defend, enhancing resistance and increasing the chances of acquiring new resistance mechanisms.

microbiology↗