Biology subjects

Gama, J. A.

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

6 recordsLinked to original sources

bioRxiv2024

Universal rules govern plasmid copy number

Plasmids -autonomously replicating DNA molecules- exhibit a broad range of replication and mobility strategies, genetic repertoires, host ranges, sizes, and copies per cell. However, the determinants of plasmid copy number (PCN) remain poorly understood. Here, we use extensive DNA sequencing data to analyse the copy number of thousands of diverse bacterial plasmids in a comprehensive manner. We find that PCN is highly variable, spanning nearly three orders of magnitude, and that it is intrinsically robust against changes in genomic context. We further show that PCN variability is tightly associated with plasmid lifestyles, and propose the concept of replicon dominance to explain interactions in widespread multi-replicon plasmids. Finally, we uncover a universal scaling law that links copy number and plasmid size across bacterial species, indicating that pervasive constraints modulate the PCN-size trade-off.

microbiology↗

bioRxiv2024

Plasmids modulate microindel mutations in Acinetobacter baylyi ADP1

Plasmids can impact the evolution of their hosts, e.g. due to carriage of mutagenic genes, through cross-talk with host genes or as result of SOS induction during transfer. Here we demonstrate that plasmids can cause microindel mutations in the host genome. These mutations are driven by the production of single-stranded DNA molecules that invade replication forks at microhomologies and subsequently get integrated into the genome. Using the gammaproteobacterial model organism Acinetobacter baylyi, we show that carriage of broad host range plasmids from different incompatibility groups can cause microindel mutations directly or indirectly. The plasmid pQLICE belonging to the incompatibility group Q (IncQ) and replicating by a characteristic strand displacement mechanism can generate chromosomal microindel mutations directly with short stretches of DNA originating from pQLICE. In addition, the presence of plasmids can increase microindel mutation frequencies indirectly (i.e., with chromosomal ectopic DNA) as shown with the IncP plasmid vector pRK415 (theta replication mechanism), presumably through plasmid-chromosome interactions that lead to DNA damages. These results provide new mechanistic insights into the microindel mutation mechanism, suggesting that single-stranded DNA repair intermediates are the causing agents. By contrast, the IncN plasmid RN3 appears to suppress host microindel mutations. The suppression mechanism remains unknown. Other plasmids in this study confer ambiguous or no quantifiable mutagenic effects.

microbiology↗

bioRxiv2023

The recombination initiation functions DprA and RecFOR suppress microindel mutations in Acinetobacter baylyi ADP1

Short-Patch Double Illegitimate Recombination (SPDIR) has been recently identified as a rare mutation mechanism. During SPDIR, ectopic DNA single-strands anneal with genomic DNA at microhomologies and get integrated in the course of DNA replication, presumably acting as Okazaki fragments. The resulting microindel mutations are highly variable in size and sequence. In the soil bacterium Acinetobacter baylyi, SPDIR mutations are tightly controlled by genome maintenance functions including RecA. In this study, we investigate the roles of DprA, RecFOR and RecBCD, which are cytoplasmic functions that load DNA single-strands with RecA. All three functions suppress SPDIR mutations in wildtype to levels below the detection limit. While SPDIR mutations are slightly elevated in the absence of DprA alone, they are strongly increased in the absence of both DprA and RecA. This SPDIR-avoiding function of DprA is not related to its role in natural transformation. These results suggest an antimutational function for DprA and offer an explanation for the ubiquity of dprA in the genomes of non-transformable bacteria.

molecular biology↗

bioRxiv2022

Consistent typing of plasmids with the mge-cluster pipeline

Extrachromosomal elements of bacterial cells such as plasmids are notorious for their importance in evolution and adaptation to changing ecology. However, high-resolution population-wide analysis of plasmids has only become accessible recently with the advent of scalable long-read sequencing technology. Current typing methods for the classification of plasmids remain limited in their scope which motivated us to develop a computationally efficient approach to simultaneously recognize novel types and classify plasmids into previously identified groups. Our method can easily handle thousands of input sequences which are compressed using a unitig representation in a de Bruijn graph. We provide an intuitive visualization, classification and clustering scheme that users can explore interactively. This provides a framework that can be easily distributed and replicated, enabling a consistent labelling of plasmids across past, present, and future sequence collections. We illustrate the attractive features of our approach by the analysis of population-wide plasmid data from the opportunistic pathogen Escherichia coli and the distribution of the colistin resistance gene mcr-1.1 in the plasmid population.

bioinformatics↗

bioRxiv2020

Cryptic β-lactamase evolution is driven by low β-lactam concentrations

Our current understanding of how low antibiotic concentrations shape the evolution of contemporary {beta}-lactamases is limited. Using the wide-spread carbapenemase OXA-48, we tested the long-standing hypothesis that selective compartments with low antibiotic concentrations cause standing genetic diversity that could act as a gateway to develop clinical resistance. Here, we subjected Escherichia coli expressing blaOXA-48, on a clinical plasmid, to experimental evolution at sub-minimum inhibitory concentrations (sub-MIC) of ceftazidime. We identified and characterized seven single variants of OXA-48. Susceptibility profiles and dose-response curves showed that they increased resistance only marginally. However, in competition experiments at sub-MIC of ceftazidime, they showed strong selectable fitness benefits. Increased resistance was also reflected in elevated catalytic efficiencies towards ceftazidime. These changes are likely caused by enhanced flexibility of the {Omega}- and {beta}5-{beta}6 loops. In conclusion, low-level concentrations of {beta}-lactams can drive the evolution of {beta}-lactamases through cryptic phenotypes which may act as stepping-stones towards clinical resistance.

evolutionary biology↗

bioRxiv2020

Piggybacking on niche-adaptation reduces the cost of multidrug resistance plasmids

The persistence of plasmids in bacterial populations represents a puzzling evolutionary problem with serious clinical implications due to their role in the ongoing antibiotic resistance crisis. Recently, major advancements have been made towards resolving this "plasmid paradox" but mainly in a non-clinical context. Here we propose an additional explanation for the maintenance of multidrug resistance (MDR) plasmids in clinical Escherichia coli strains. After co-evolving two MDR plasmids encoding last resort carbapenem resistance with an extraintestinal pathogenic E. coli strain, we observed that chromosomal media adaptive mutations in the global regulatory systems CCR (Carbon Catabolite Repression) and ArcAB (Aerobic Respiration Control) pleiotropically mitigated the costs of both plasmids. Mechanistically, cost reductions were due to a net downregulation of plasmid gene expression. Our results suggest that global chromosomal transcriptional re-wiring during bacterial niche-adaptation may facilitate plasmid maintenance.

microbiology↗