Biology subjects

Laderman, E.

Publications and source records attributed to Laderman, E..

5 recordsLinked to original sources

bioRxiv2026

Deep sequencing artificially inflates estimates of microbial diversity

Sequencing artifacts challenge accuracy and reproducibility when quantifying microbial diversity. To track error propagation in microbiome analyses, we analyze no-diversity amplicons, which are amplified from host genes with limited genetic diversity or from synthetic spike-ins. We find that sequencing at greater than 104 reads exponentially increased no-diversity amplicon sequence variant (ASV) richness, with hundreds of ASVs observed per sample. This striking pattern was shared with microbial amplicons (16S rRNA, ITS, gyrB, rpoB), which revealed inflated Shannon diversity with an increase in read counts for both the community and within taxa. Comparing sequencing error profiles between no-diversity and microbial amplicons showed that truncating reads to shorter lengths and use of the AVITI Element platform can mitigate, but not abolish, the impacts of artificial inflation; we recommend caution when read depths vary orders of magnitude between samples. Overall, utilizing no-diversity amplicons can help optimize parameters to improve estimates of microbial diversity.

ecology↗

bioRxiv2025

Seasonality, land use, and diversity shape microbiome-pathogen interactions in wild populations of Arabidopsis thaliana

The microbiome often protects plants against pathogens, but most findings are limited to controlled experiments in the lab. In the context of wild populations, one key challenge is to understand sources of variation that impact the commensal microbiome, which in turn shapes the degree of protection. Here, we surveyed both disease symptoms and microbiomes from wild populations of Arabidopsis thaliana over four consecutive seasons (fall/spring) across three different land use types. Land use types varied in the extent of anthropogenic influences and included forest meadows, human-impacted fields adjacent to agriculture or municipal parks, and highly disturbed habitats near railroad tracks. By building an integrative map of abiotic and biotic variables, we find that a key predictor of disease was biodiversity across ecological scales. Plant communities with higher diversity were associated with reduced disease burden in A. thaliana populations but also increased diversity within the microbiome of A. thaliana. This increased microbial diversity was additionally associated with less disease in A. thaliana. However, the diversity-microbiome-disease relationships were all sensitive to season and further modulated by land use. Taken together, our work highlights the importance of anthropogenic change reshaping species interactions across ecological scales to impact disease risk in wild plant populations.

ecology↗

bioRxiv2025

Negative frequency-dependent selection contributes to modular structure of effector repertoires in Pseudomonas syringae

The evolutionary fate of multi-strain pathogens is shaped by host-pathogen ecological interactions. In bacterial pathogens of plants, enhanced strain characterization and advances in our understanding of molecular mechanisms underlying defense pathways open the door for revisiting the role of negative frequency-dependent selection (NFDS) in strain structure, including its interplay with genetic exchange. NFDS arising from specific defense is one potential mechanism for generating, maintaining, and structuring pathogen diversity. In plants, specific protection against microbial pathogens involves Resistance proteins (R-proteins) that recognize virulence factors (effectors) secreted by pathogens, typically to subvert the initial line of host defense. Here we formulate a stochastic computational co-evolution model that explicitly incorporates variable length R-gene and effector repertoires, and migration from their regional pools. We use this model to understand potential mechanisms shaping effector repertoire structure and associated strain coexistence in the generalist plant pathogen P. syringae. The demonstration of a modular structure in our numerical simulations motivates the analysis of genome sequences from 76 strains collected in the Midwestern US and 1104 strains from global sources. We find that effector repertories both locally and globally exhibit a modular structure, with higher similarity within than between clusters. The observed modules are consistent with the core genome phylogeny and are unexplained by plant host species, location of isolation, and genetic linkage between effectors. An extension of the model is needed to take into account the evidence for genetic exchange and the phylogenetic congruence of effector modules. We initialize the system with a phylogenetically congruent modular structure and include recombination rates decreasing as a function of phylogenetic distance. We show that NFDS can counter-balance the effects of mixing due to recombination and in so doing, contributes to the maintenance of strain structure. These findings indicate that the observed similarity clusters may constitute, in part, emergent niches arising from eco-evolutionary dynamics that contribute to strain coexistence.

ecology↗

bioRxiv2023

Parallelized screening of virus accessory genes reveals diverse defense and counter-defense mechanisms

Viruses have been evolving host-modifying factors for billions of years. Genomes of bacterial and archaeal viruses are replete with fast-evolving, uncharacterized accessory genes (AGs), most of which likely antagonize host defenses or other viruses1, 2. Systematic investigation of AGs could uncover a multitude of biological mechanisms involved in virus-host competition, but AG identification in genomic databases remains a challenge. We developed an integrated computational and high-throughput discovery platform to identify AGs in virus genomes and assay their functions in complementary phage infection-dependent and -independent contexts. Our approach showcases how phages interact with the principal layers of antiviral immunity, including cell surface modifications, restriction systems, and abortive infection (Abi) mechanisms, which operate simultaneously in the same host. We discovered multiple Enterobacteriophage AGs associated with counter-defense functions that activate rather than inhibit antiviral immunity in cells, including the surprising finding that anti-restriction AGs elicit programmed cell death (PCD) activity of some restriction-modification (R-M) systems. We propose that counter-defense AGs that trigger PCD create a conundrum for phages whereby keeping the AGs causes PCD but losing them exposes the phage to restriction by bacteria. Strategies employed by viruses to avoid this double jeopardy could be an important factor in virus evolution that remains to be explored.

microbiology↗

bioRxiv2022

Core Defense Hotspots within Pseudomonas aeruginosa are a consistent and rich source of anti-phage defense systems

Bacteria use a diverse arsenal of anti-phage immune systems, including CRISPR-Cas and restriction enzymes. Identifying the full defense repertoire of a given species is still challenging, however. Here, we developed a computational tool to broadly identify anti-phage systems, which was applied to >180,000 genomes available on NCBI, revealing Pseudomonas aeruginosa to possess the most diverse anti-phage arsenal of any species with >200 sequenced genomes. Using network analysis to identify the common neighbors of anti-phage systems, we surprisingly identified two highly conserved core defense hotspot loci (cDHS1 and cDHS2). Across more than 1,000 P. aeruginosa strains, cDHS1 is up to 224 kb (mean: 34 kb) with varied arrangements of at least 31 immune systems while cDHS2 has 24 distinct systems (mean: 15.4 kb). cDHS1/2 are present in most P. aeruginosa isolates, in contrast to highly variable mobile DHSs. Most cDHS genes are of unknown function potentially representing new anti-phage systems, which we validated by identifying a novel anti-phage system (Shango) commonly encoded in cDHS1. Identification of core gene markers that flank immune islands could be a simple approach for immune system discovery and may represent popular landing spots for diverse MGEs carrying anti-phage systems.

genomics↗