Biology subjects

Martinez, J. A.

Publications and source records attributed to Martinez, J. A..

14 recordsLinked to original sources

bioRxiv2026

Dual control of plasmid copy number in E. coli by combining temperature shifts and RNAI-based genetic circuits for tunable replication dynamics

Plasmid copy number (PCN) is a central determinant of recombinant gene expression levels and metabolic burden in bacterial cell factories. However, dynamic real-time control of PCN during microbial cultivation remains largely unexplored. In the ColE1/pUC19 replication system, PCN is governed by an antisense RNAI/RNAII circuit, but this native mechanism provides no external handle for process-level intervention. Here, we engineer and characterize a dual-layer control architecture that combines two orthogonal perturbations to direct plasmid replication in Escherichia coli populations i.e., temperature shifts, which modulate the secondary structure of RNAII and, consequently, its binding to RNAI and its inhibitory potency (ex vivo control), and arabinose-inducible overexpression of a supplementary RNAI cassette, integrated either on a secondary low-copy plasmid or directly on the high-copy target plasmid (in vivo control). Using a superfolder GFP validated fluorescent reporter and automated flow cytometry in continuous cultures, we track PCN dynamics at the population level in real time under chemostat conditions. Preliminary screening in microplates high-throughput cultivation device across three strains, two carbon sources, and three temperatures (30, 37, and 42C) reveals that the two control layers act synergistically. Neither temperature alone nor inducible RNAI alone achieves the dynamic range obtained by their combination. This synergistic effect is sustained during continuous cultivation at a fixed dilution rate of 0.1/h, with carbon source and temperature transitions producing predictable and reproducible shifts in population-level PCN. These results establish a scalable, dual-input framework for on-demand PCN tuning in continuous bioprocesses, with direct relevance to biopharmaceutical plasmid production and synthetic biology applications.

bioengineering↗

bioRxiv2026

Zebrafish screen of schizophrenia risk genes reveals convergent dysregulation of cholesterol metabolism

Rare coding variants provide a tractable entry point for understanding the molecular mechanisms underlying schizophrenia risk. Here, we generated and characterized zebrafish lines with mutations in the orthologs of >20 human schizophrenia-associated genes, including eight of the top ten SCHEMA genes, genes disrupted in childhood-onset schizophrenia (COS), and genes located within recurrent copy number variants. Whole-brain phospho-Erk activity mapping and behavioral profiling identified phenotypes in multiple mutant lines. We prioritized a protein-truncating mutation in sp4, which encodes an activity-dependent transcription factor, and a COS-associated missense mutation in atp1a3a, which encodes a Na+/K+ ATPase pump, for additional characterization. Both knockout and point mutations in atp1a3a disrupted brain activity and behavior in larvae and impaired navigation of a Y-maze in juveniles. Bulk RNA sequencing data from adult sp4 and atp1a3a brains highlighted convergent upregulation of sterol biosynthesis pathways, including increased expression of srebf2 and msmo1. Analysis of previously published telencephalon single-cell data demonstrated that cholesterol synthesis genes are enriched in astrocyte-like cells and increase in expression during post-larval development. Consistent with transcriptomic findings, filipin staining indicated increased free cholesterol in juvenile sp4 and atp1a3a mutant brains. Our findings identify dysregulation of glial and sterol-associated programs as a shared molecular consequence of two distinct schizophrenia risk mutations. Although whether sterol pathway dysregulation represents a primary pathogenic mechanism or a secondary response to changes in neuronal activity requires further investigation, the convergence observed between genetic models and developmental stages suggests that disruptions to lipid homeostasis could represent a shared feature of schizophrenia disease biology.

genetics↗

bioRxiv2026

StrIPETrack: a real-time, ROI-flexible tracking platform for high-throughput zebrafish behavior

Quantitative phenotyping is essential to studies of animal behavior, enabling systematic analysis of variation arising from natural diversity or experimental manipulation. High-throughput behavioral assays that can simultaneously test multiple animals support sufficiently powered studies of behavioral variation, but accurate tracking of each animal is critical. Furthermore, behavioral tasks and experimental arenas span a wide range of complexity, from the reaction of a single larval zebrafish to an acoustic stimulus to associative conditioning in cue-rich environments. Here, we developed and validated StrIPETrack (Structural similarity-based Image Processing for Estimation and Tracking), a Python-based, modular animal tracking software designed for flexible region-of-interest (ROI) definitions and extensibility across assays. We show that StrIPETrack measures activity comparably to our previous LabVIEW-based zebrafish tracking software and detects similar behavioral differences between wild-type clutches. In addition, StrIPETrack accurately captures behavior in a complex arena: the Y-maze. Our approach for analyzing Y-maze navigation yields an expanded set of metrics beyond turn count and direction, revealing more subtle behavioral variation. Overall, this versatile software can be applied to monitor the activity of multiple animals in parallel in both simple high-throughput and more complex assays, and can be readily adapted to new paradigms. SummaryOur open-source tracking software provides rich behavioral phenotyping of animals in many behavioral tasks. The flexible ROI design and live tracking makes the software adaptable to diverse paradigms.

animal behavior and cognition↗

bioRxiv2026

Prioritizing Neuroactive Ligands Using Motif-Guided Virtual Discovery and Zebrafish Profiling

Virtual screening of ultra-large chemical libraries is a highly effective strategy for early-stage drug discovery. However, these pipelines often yield thousands of molecules that pass computational filters, and in silico-derived interaction energies do not consistently predict experimental efficacy. Furthermore, many high-affinity hits do not necessarily function effectively in an organism with tissues, barriers, and extensive off-target possibilities. A major hurdle in drug discovery is the prioritization of top candidates for rodent testing. Here, we introduce Rosetta Engine for Anchoring Ligands with a Motif ("REAL-M"), a novel computational screening algorithm that uses structural interaction data from the Protein Data Bank (PDB) to guide ligand placement and selection. Using the hypocretin receptor as a test case for this computational pipeline, 28 of 30 predicted antagonists significantly blocked binding of the cognate peptide agonist in a PRESTO-Tango cell-based reporter assay, including six chemically diverse molecules with comparable efficacy to preexisting antagonists. Three of the six molecules significantly mitigated hypocretin-induced larval zebrafish hyperactivity. Secondary testing with a zebrafish hcrtr2 null mutant ensured that behavioral phenotypes were not due to off-target interactions, which we did observe with preexisting antagonists. This pipeline is readily adaptable to the thousands of zebrafish proteins with highly conserved binding pockets.

pharmacology and toxicology↗

bioRxiv2025

Synthetic niches enable co-culture bioprocessing but are prone to mutational escape

Stabilizing microbial co-cultures is a central challenge for bioproduction. While division of labor between strains can enhance efficiency, it often results in population instability over time. Classical strategies, including cross-feeding, quorum sensing, and toxin-antitoxin modules, often rely on complex ecological interactions that are difficult to predict or maintain under bioprocess conditions. Here, we introduce synthetic niches as an alternative framework, using genetic toggle switches that couple growth to defined phenotypic states. We engineered two auxotrophic strains, TOGGLE_green and TOGGLE_yellow, in which growth is linked to either GFP- or YFP-expressing states and assessed their behavior in continuous bioreactor cultures using automated flow cytometry. Unexpectedly, the introduction of auxotrophic pressure reshaped circuit function i.e., instead of maintaining bistability, toggle strains behaved as unidirectional inducible systems that reverted upon inducer withdrawal. This feature enabled simplified control with a single input but also revealed a vulnerability to mutational escape under intensified cultivation. A simple repression-based ODE model recapitulated the reversible dynamics, but deviations under prolonged operation highlighted the rapid evolutionary erosion of control. Our findings demonstrate both the potential and the limitations of synthetic niches for co-culture engineering and emphasize the need to integrate evolutionary robustness into the design of next-generation bioprocess control strategies.

synthetic biology↗

bioRxiv2025

Overriding bioprocess perturbations with a cell machine interface for reliable microbial stress-response control

Controlling cell population dynamics and phenotypic diversification is a key objective in systems and synthetic biology, particularly for ensuring uniform responses from engineered gene circuits. While cell-machine interfaces have been employed to modulate host-gene circuit interactions, environmental perturbations typical of industrial bioreactor conditions remain underexplored. In this study, we investigate the impact of such perturbations on the general stress response in Escherichia coli and Saccharomyces cerevisiae. Using scale-down bioreactor experiments, we evaluate the performance of the Segregostat, a real-time control system that leverages automated flow cytometry to induce dynamic nutrient shifts. The Segregostat achieves robust stress response control, even under severe perturbations such as extended residence times in a two-compartment reactor. We hypothesize that this robustness arises from the systems ability to amplify host-compatible fluctuations beyond bioreactor-induced perturbations. Our findings highlight the importance of integrating environmental factors into control strategies for reliable gene circuit behavior in industrial bioprocessing environments.

bioengineering↗

bioRxiv2025

A Fitness Entropy Compensation effect set the trade-off between growth and gene expression in cell populations

We present findings on a Fitness-Entropy Compensation (FEC) mechanism which offsets the activation of gene circuits that compromise survival. It counteracts the resulting fitness reduction by increasing the diversity in gene expression among individual cells within the population. This diversity, quantified by the Shannon entropy, enables cells with lower expression levels to support the survival of the entire population. We investigated the presence of FEC in a range of synthetic and stress-related genetic circuits in continuous culture. Our results reveal that it effectively stabilizes cell populations by mitigating the detrimental trade-offs between growth and gene expression. This stabilization is due to the reduced growth rate of the induced phenotype that leads to environmental changes, decreases induction strength, and promotes escape from unfit states. These findings suggest that the FEC mechanism may be a universal strategy for stabilization in various cellular systems and set the basis for a quantitative description of the trade-off between growth and gene expression and its consequences at the population level.

systems biology↗

bioRxiv2025

Enantiomer-Specific Malathion Degradation by Gut Microbes of the Colorado Potato Beetle

Symbiotic microbes play pivotal roles in insect ecology, including the detoxification of insecticides, which reduces target host mortality and diminishes the efficacy of chemical pest control agents. Quantifying the prevalence of symbiont-mediated insecticide detoxification across the microbiome is necessary to understand its contributions to pesticide resistance, and to understand how pesticides alter gut microbial communities. Here, we investigated the prevalence and mechanisms of pesticide degradation within the gut microbiota of the Colorado potato beetle (Leptinotarsa decemlineata), a significant agricultural pest that has driven ongoing insecticide innovation for decades. Beetles were collected from an organic farm in Tyler, TX, and 18 bacterial isolates representing the diversity of their gut microbiota were screened for their ability to degrade three common insecticides in vitro: imidacloprid, fenitrothion, and malathion. Among these, Acinetobacter calcoaceticus, Pseudomonas protegens, and an unnamed Microbacterium species degraded malathion as a sole carbon source, with distinct enantiomer-specific preferences. Untargeted GC-MS analysis revealed breakdown products, providing initial insights into the metabolic pathways utilized by these microbes. These findings suggest that microbial association with resistant insect hosts may select for microbial insecticide utilization, potentially enhancing resistance development in agricultural pests and influencing the surrounding soil microbiome.

microbiology↗

bioRxiv2023

Release of extracellular DNA by Pseudomonas species as a major determinant for biofilm switching and an early indicator for cell population control

Withdrawal StatementThe authors have withdrawn this manuscript due to a duplicate posting of manuscript number BIORXIV/2021/430776. Therefore, the authors do not wish this work to be cited as reference for the project. If you have any questions, please contact the corresponding author. The correct preprint can be found at doi: 10.1101/2021.02.11.430776

microbiology↗

bioRxiv2023

Thioredoxin regulates the redox state and the activity of the human tRNA ligase complex

The mammalian tRNA ligase complex (tRNA-LC) catalyzes the splicing of intron-containing pre-tRNAs in the nucleus and the splicing of XBP1 mRNA during the unfolded protein response (UPR) in the cytoplasm. We recently reported that the tRNA-LC co-evolved with PYROXD1, an essential oxidoreductase that protects the catalytic cysteine of RTCB, the catalytic subunit of the tRNA-LC, against aerobic oxidation. In this study we show that the oxidoreductase Thioredoxin (TRX) preserves the enzymatic activity of RTCB under otherwise inhibiting concentrations of oxidants. TRX physically interacts with oxidized RTCB, and reduces and re-activates RTCB through the action of its redox-active cysteine pair. We further show that TRX interacts with RTCB at late stages of UPR. Since the interaction requires oxidative conditions, our findings suggest that prolonged UPR generates reactive oxygen species. Thus, our results support a functional role for TRX in securing and repairing the active site of the tRNA-LC, thereby allowing pre-tRNA splicing and UPR to occur when cells encounter mild, but still inhibitory levels of reactive oxygen species.

biochemistry↗

bioRxiv2022

Controlling microbial co-culture based on substrate pulsing can lead to stability through differential fitness advantages

Microbial consortia are an exciting alternative for increasing the performances of bioprocesses for the production of complex metabolic products. However, the functional properties of microbial communities remain challenging to control, considering the complex interaction mechanisms occurring between co-cultured microbial species. Indeed, microbial communities are highly dynamic and can adapt to changing environmental conditions through complex mechanisms, such as phenotypic diversification. We focused on stabilizing a co-culture of Saccharomyces cerevisiae and Escherichia coli in continuous cultures. Our preliminary data pointed out that transient diauxic shifts could lead to stable co-culture by providing periodic fitness advantages to the yeast. Based on a computational toolbox called MONCKS (for MONod-type Co-culture Kinetic Simulation), we were able to predict the dynamics of diauxic shift for both species based on a cybernetic approach. This toolbox was further used to predict the frequency of diauxic shift to be applied to reach co-culture stability. These simulations were successfully reproduced experimentally in continuous bioreactors with glucose pulsing. Finally, based on a bet-hedging reporter, we observed that the yeast population exhibited an increased phenotypic diversification process in co-culture compared with mono-culture, suggesting that this mechanism could be the basis of the metabolic fitness of the yeast.

systems biology↗

bioRxiv2021

Reducing phenotypic and genotypic instabilities of microbial population during continuous cultivation based on stochastic switching dynamics

Predicting the fate of a microbial population (i.e., growth, gene expression...) remains a challenge, especially when this population is exposed to very dynamic environmental conditions, such as those encountered during continuous cultivation. Indeed, the dynamic nature of continuous cultivation process implies the potential deviation of the microbial population involving genotypic and phenotypic diversification. This work has been focused on the induction of the arabinose operon in Escherichia coli as a model system. As a preliminary step, the GFP level triggered by an arabinose-inducible ParaBAD promoter has been tracked by flow cytometry in chemostat with glucose-arabinose co-feeding. For a large range of glucose-arabinose co-feeding, the simultaneous occurrence of GFP positive and negative subpopulation was observed. In a second set of experiments, continuous cultivation was performed by adding either glucose or arabinose, based on the ability of individual cells for switching from low GFP to high GFP states, according to a technology called segregostat. In segregostat mode of cultivation, on-line flow cytometry analysis was used for adjusting the arabinose/glucose transitions based on the phenotypic switching capabilities of the microbial population. This strategy allowed finding an appropriate arabinose pulsing frequency, leading to a prolonged maintenance of the induction level with limited impact on phenotypic diversity for more than 60 generations. This result suggests that constraining individual cells into a given phenotypic trajectory is maybe not the best strategy for directing cell population. Instead, allowing individual cells switching around a predefined threshold seems to be a robust strategy leading to oscillating, but predictable, cell population behavior.

microbiology↗

bioRxiv2020

Occurrence and characterization of cyst nematode species (Globodera spp.) associated with potato crops in Colombia

Potato cyst nematodes (PCN) from the genus Globodera spp. cause major losses in potato (Solanum tuberosum) industry worldwide. Despite their importance, at present little is known about the status of this plant pathogen in cultivated potatoes in Colombia. In this study, a total of 589 samples collected from 75 geographic localities from nine potato producing departments of Colombia were assayed for the presence of potato cyst nematodes. Fifty-seven percent of samples tested positive for PCN. All populations but one were identified as Globodera pallida, with conspicuous morphometric variation found among populations. Based on phylogenetic analysis of the internal transcribed spacer region (ITS1-5.8S-ITS2) of the rRNA gene and D2-D3 expansion segments of the 28S rRNA gene, G. pallida from Colombia formed a monophyletic group closely related to Peruvian populations, with the lowest average number of nucleotide substitutions per site (Dxy= 0.002) and net nucleotide substitutions per site (Da= 0.001), when compared to G. pallida populations from South, North America and Europe. A single sample formed a well-supported subclade along with G. rostochiensis and G. tabacum from Japan, USA and Argentina. To our knowledge this is the first comprehensive survey of Globodera populations from Colombia that includes morphological and genetic data. Our findings on species diversity and phylogenetic relationships of Globodera populations from Colombia may help elucidate the status and distribution of Globodera species, and lead to the development of accurate management strategies for the potato cyst nematodes.

zoology↗

bioRxiv2017

Lack of Evidence that Ursodeoxycholic Acid’s Effects on the Gut Microbiome Influence Colorectal Adenoma Risk

ObjectiveWe previously reported that Ursodeoxycholic acid (UDCA), a therapeutic bile acid, reduces risk for advanced colorectal adenoma in men but not women. Interactions between the gut microbiome and fecal bile acid composition as a factor in colon cancer neoplasia have been postulated but evidence is limited to small cohorts and animal studies.\n\nDesignUsing banked stool samples collected as part of a phase III randomized clinical trial of UDCA for the prevention of colorectal neoplasia, we compared change in the microbiome composition after 3 years intervention in a subset of participants randomized to 8-10 mg/kg of body weight UDCA (n=198) to placebo (n=203). UDCA effects on the microbiome, sex and adenoma outcome were investigated.\n\nResultsStudy participants randomized to UDCA experienced compositional changes in their microbiome that were statistically more similar to other individuals in the UDCA arm than to those in the placebo arm. This change reflected an UDCA-associated shift in microbial community distance metrics (P <0.001), independent of sex, with no evidence of UDCA effect on microbial richness (P > 0.05). These UDCA-associated shifts in microbial community distance metrics from baseline to end-of-study were not associated with risk of any or advanced adenoma (all P> 0.05) in men or women.\n\nConclusionDespite a large sampling of randomized clinical trial participants, daily UDCA use only modestly influenced the relative abundance of microbial species in stool with no evidence for effects of UDCA on stool microbial community composition as a modifier of colorectal adenoma risk.\n\nSUMMARYO_ST_ABSWhat is already known about this subject?C_ST_ABSO_LIUrsodeoxycholic acid (UDCA) is a therapeutic bile acid used in the treatment of primary biliary cirrhosis (PBC) and investigated for anti-cancer activity in the colon\nC_LIO_LIIn humans, UDCA is produced in the colon from the conjugation of primary bile acids by intestinal bacteria\nC_LIO_LIIntestinal bacteria play a critical role in human intestinal health and disease including a hypothesized role in the development of colorectal cancer.\nC_LIO_LIUDCA was found to reduce the risk of more advanced colorectal adenoma with effects present in men but not women.\nC_LIO_LITherapeutic UDCA was recently shown to reduce the extent of bacterial dysbiosis in patients with PBC\nC_LI\n\nWhat are the new findings?O_LIAmong a population of patients with colorectal adenoma, low dose oral UDCA taken daily produced modest changes in fecal bacterial composition\nC_LIO_LIUDCA associated changes in the gut microbiome were similar in men and women.\nC_LIO_LIUDCA associated changes in the gut micobiome were not associated with risk of any or advanced colorectal adenoma in the patient population.\nC_LI\n\nHow might it impact on clinical practice in the foreseeable future?O_LIThese findings confirm effects of oral UDCA on the microbiome that may be beneficial for patients with PBC.\nC_LIO_LIThese findings suggest that the anti-cancer effects of UDCA for colorectal adenoma prevention are not due to major effects of UDCA on the gut microbiome.\nC_LI

cancer biology↗