Biology subjects

Rojas-Montero, M.

Publications and source records attributed to Rojas-Montero, M..

5 recordsLinked to original sources

bioRxiv2025

Bacteriophage genome-wide transposon mutagenesis

Bacteriophages have genomes that span a wide size range, are densely packed with coding sequences, and frequently encode genes of unknown function. Classical forward genetics has defined essential genes for phage replication in a few model systems but remains laborious and non-scalable. Unbiased functional genomics approaches are therefore needed for phages, particularly for large lytic phages. Here, we develop a phage transposon sequencing (TnSeq) platform that uses the mariner transposase to insert an anti-CRISPR selectable marker into phage genomes. CRISPR-Cas13a-based enrichment of transposed phages followed by pooled sequencing identifies both fitness-conferring and dispensable genes. Using the Pseudomonas aeruginosa-infecting nucleus-forming jumbo phage {Phi}KZ (280,334 bp; 371 predicted genes) as a model, we show that [~]110 genes are fitness-conferring via phage TnSeq. These include conserved essential genes involved in phage nucleus formation, protein trafficking, transcription, DNA replication, and virion assembly. We also isolate hundreds of individual phages with insertions in non-essential genes and reveal conditionally essential genes that are specifically required in clinical isolates, at environmental temperature, or in the presence of a defensive nuclease. Phage TnSeq is a facile, scalable technology that can define essential phage genes and generate knockouts in all non-essential genes in a single experiment, enabling conditional genetic screens in phages and providing a broadly applicable resource for phage functional genomics.

microbiology↗

bioRxiv2025

Reverse transcribed ssDNA derepresses translation of a retron antiviral protein

Retrons are bacterial immune systems that prevent the spread of phages by initiating a toxic response within infected hosts. All previously characterized retrons produce high levels of multicopy single-stranded DNA (msDNA) in the cell by reverse transcription, which acts as an antitoxin in the absence of phage infection. However, we describe here a non-canonical mechanism for Type VI retrons, which do not produce detectable msDNA in the absence of phage, yet still provide phage defense. Focusing primarily on Retron-Vpa2, a Type VI retron from Vibrio parahaemolyticus, we show broad defense against phages and identify triggers of the system within phage recombination systems. Within the Retron-Vpa2 operon, we find a highly enriched, structured transcript that we term a hybrid RNA (hyRNA), which contains both the retrons reverse transcription template and a translationally repressed toxic effector coding sequence. We find that phage infection induces the accumulation of high levels of msDNA and that this msDNA is necessary for derepressing translation of the antiviral toxin. These findings present key biological and mechanistic insights into a distinct group of retrons while highlighting the diversity of systems that participate in bacterial immunity.

microbiology↗

bioRxiv2025

Phage defense and genome editing using novel retrons sourced from isolated environmental bacteria

Retrons are bacterial immune systems that protect a bacterial population against phages by killing infected hosts. Retrons typically comprise a reverse transcriptase, a template noncoding RNA that is partially reverse transcribed into RT-DNA, and a toxic effector. The reverse transcriptase, noncoding RNA, and RT-DNA complex sequester the toxic effector until triggered by phage infection, at which point the toxin is released to induce cell death. Due to their ability to produce single-stranded DNA in vivo, retrons have also been engineered to produce donor templates for genome editing in both prokaryotes and eukaryotes. However, the current repertoire of experimentally characterized retrons is limited, with most retrons sourced from clinical and laboratory strains of bacteria. To better understand retron biology and natural diversity, and to expand the current toolbox of retron-based genome editors, we developed a pipeline to isolate retrons and their bacterial hosts from a variety of environmental samples. Here, we present six of these novel retrons, each isolated from a different host bacterium. We characterize the full operon of these retrons and test their ability to defend against a panel of E. coli phages. For two of these retrons, we further unravel their mechanism of defense by identifying the phage genes responsible for triggering abortive infection. Finally, we engineer these retrons for genome editing in E. coli, demonstrating their potential use in a biotechnological application.

microbiology↗

bioRxiv2024

An experimental census of retrons for DNA production and genome editing

Retrons are bacterial immune systems that use reverse transcribed DNA as a detector of phage infection. They are also increasingly deployed as a component of biotechnology. For genome editing, for instance, retrons are modified so that the reverse transcribed DNA (RT-DNA) encodes an editing donor. Retrons are commonly found in bacterial genomes; thousands of unique retrons have now been predicted bioinformatically. However, only a small number have been characterized experimentally. Here, we add substantially to the corpus of experimentally studied retrons. We synthesized >100 previously untested retrons to identify the natural sequence of RT-DNA they produce, quantify their RT-DNA production, and test the relative efficacy of editing using retron-derived donors to edit bacterial genomes, phage genomes, and human genomes. We add 62 new empirically determined, natural RT-DNAs, which are not predictable from the retron sequence alone. We report a large diversity in RT-DNA production and editing rates across retrons, finding that top performing editors outperform those used in previous studies, and are drawn from a subset of the retron phylogeny.

bioengineering↗

bioRxiv2023

Simultaneous multi-site editing of individual genomes using retron arrays

Our understanding of genomics is limited by the scale of our genomic technologies. While libraries of genomic manipulations scaffolded on CRISPR gRNAs have been transformative, these existing approaches are typically multiplexed across genomes. Yet much of the complexity of real genomes is encoded within a genome across sites. Unfortunately, building cells with multiple, non-adjacent precise mutations remains a laborious cycle of editing, isolating an edited cell, and editing again. Here, we describe a technology for precisely modifying multiple sites on a single genome simultaneously. This technology - termed a multitron - is built from a heavily modified retron, in which multiple donor-encoding msds are produced from a single transcript. The multitron architecture is compatible with both recombineering in prokaryotic cells and CRISPR editing in eukaryotic cells. We demonstrate applications for this approach in molecular recording, genetic element minimization, and metabolic engineering.

bioengineering↗