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1. Kairos infers in situ horizontal gene transfer in longitudinally sampled microbiomes through microdiversity-aware sequence analysis

   https://doi.org/10.1101/2023.10.24.563791  

   Brown, Connor L; Cheung, Yat Fei; Song, Haoqiu; Snead, Delaney; Vikesland, Peter; Pruden, Amy; Zhang, Liqing (October 2023, bioRxiv)

   Abstract Horizontal gene transfer (HGT) occurring within microbiomes is linked to complex environmental and ecological dynamics that are challenging to replicate in controlled settings. Consequently, most extant studies of microbiome HGT are either simplistic experimental settings with tenuous relevance to real microbiomes or correlative studies that assume that HGT potential is a function of the relative abundance of mobile genetic elements (MGEs), the vehicles of HGT. Here we introduce Kairos as a bioinformatic tool deployed in nextflow for detecting HGT events “in situ,” i.e., within a microbiome, through analysis of time-series metagenomic sequencing data. Thein-situframework proposed here leverages available metagenomic data from a longitudinally sampled microbiome to assess whether the chronological occurrence of potential donors, recipients, and putatively transferred regions could plausibly have arisen due to HGT over a range of defined time periods. The centerpiece of the Kairos workflow is a novel competitive read alignment method that enables discernment of even very similar genomic sequences, such as those produced by MGE-associated recombination. A key advantage of Kairos is its reliance on assemblies rather than metagenome assembled genomes (MAGs), which avoids systematic exclusion of accessory genes associated with the binning process. In an example test-case of real world data, use of assemblies directly produced a 264-fold increase in the number of antibiotic resistance genes included in the analysis of HGT compared to analysis of MAGs with MetaCHIP. Further,in silicoevaluation of contig taxonomy was performed to assess the accuracy of classification for both chromosomally- and MGE-derived sequences, indicating a high degree of accuracy even for conjugative plasmids up to the level of class or order. Thus, Kairos enables the analysis of very recent HGT events, making it suitable for studying rapid prokaryotic adaptation in environmental systems without disturbing the ornate ecological dynamics associated with microbiomes. Current versions of the Kairos workflow are available here:https://github.com/clb21565/kairos. 

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2. mGem: Tapping into the language of symbiosis to advance human microbiome research

   https://doi.org/10.1128/mbio.03661-25  

   Lewin, Gina R; Khadempour, Lily (July 2026, mBio)

   Whiteley, Marvin (Ed.)

   In human microbiome research, the term “commensal” is often used to describe organisms that benefit their hosts. In ecology, in host-microbe symbiosis, a commensal organism has no impact on its host, whereas a mutualist organism benefits its host. While others have recognized this discrepancy in terminology use, old habits are hard to break, and the human microbiome community has continued in this vein. This is our call to action for the human microbiome community to use more precise terminology that appropriately reflects the impact that these microbes have on their hosts. We should use the terms “commensal” and “mutualist” when we know the effect on the host, and “symbiont” when we do not. By using the same terminology as ecologists, we will be able to make use of, and contribute to the vast research in the field of symbiosis. 

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3. For colonization success, should hosts and microbes travel alone, together, or swap partners along the way?

   https://doi.org/10.1101/2025.10.27.684839  

   Usui, Takuji; Yu, Jingcheng; Frederickson, Megan E (October 2025, bioRxiv)

   ABSTRACT Understanding what determines colonization success is a key challenge of global change ecology. Microbiomes that enhance host performance are likely to be co-introduced with hosts during colonization due to their intimate association. Yet, it is unclear how co-introduced microbes will impact host colonization, as both the microbiome and its effects could vary upon introduction into a new habitat. Here, we used duckweeds —a cosmopolitan, freshwater angiosperm— and their microbiome to track colonization dynamics during an experimental co-introduction in the wild. Notably, we found that host performance was substantially reduced when plants were co-introduced with microbes non-local to the introduced habitat, relative to hosts with a local microbiome. Moreover, negative impacts from the non-local microbiome persisted for multiple host generations despite a rapid turnover in microbiome composition during colonization. Overall, we suggest that considering the co-introduced microbiome can help predict host colonization success under global change. 

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4. Modeling the ecology of parasitic plasmids

   https://doi.org/10.1038/s41396-021-00954-6  

   Lopez, Jaime G.; Donia, Mohamed S.; Wingreen, Ned S. (April 2021, The ISME Journal)

   null (Ed.)

   Abstract Plasmids are autonomous genetic elements that can be exchanged between microorganisms via horizontal gene transfer (HGT). Despite the central role they play in antibiotic resistance and modern biotechnology, our understanding of plasmids’ natural ecology is limited. Recent experiments have shown that plasmids can spread even when they are a burden to the cell, suggesting that natural plasmids may exist as parasites. Here, we use mathematical modeling to explore the ecology of such parasitic plasmids. We first develop models of single plasmids and find that a plasmid’s population dynamics and optimal infection strategy are strongly determined by the plasmid’s HGT mechanism. We then analyze models of co-infecting plasmids and show that parasitic plasmids are prone to a “tragedy of the commons” in which runaway plasmid invasion severely reduces host fitness. We propose that this tragedy of the commons is averted by selection between competing populations and demonstrate this effect in a metapopulation model. We derive predicted distributions of unique plasmid types in genomes—comparison to the distribution of plasmids in a collection of 17,725 genomes supports a model of parasitic plasmids with positive plasmid–plasmid interactions that ameliorate plasmid fitness costs or promote the invasion of new plasmids. 

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5. A ridge-to-reef ecosystem microbial census reveals environmental reservoirs for animal and plant microbiomes

   https://doi.org/10.1073/pnas.2204146119  

   Amend, Anthony S.; Swift, Sean O.; Darcy, John L.; Belcaid, Mahdi; Nelson, Craig E.; Buchanan, Joshua; Cetraro, Nicolas; Fraiola, Kauaoa M.; Frank, Kiana; Kajihara, Kacie; et al (August 2022, Proceedings of the National Academy of Sciences)

   Microbes are found in nearly every habitat and organism on the planet, where they are critical to host health, fitness, and metabolism. In most organisms, few microbes are inherited at birth; instead, acquiring microbiomes generally involves complicated interactions between the environment, hosts, and symbionts. Despite the criticality of microbiome acquisition, we know little about where hosts’ microbes reside when not in or on hosts of interest. Because microbes span a continuum ranging from generalists associating with multiple hosts and habitats to specialists with narrower host ranges, identifying potential sources of microbial diversity that can contribute to the microbiomes of unrelated hosts is a gap in our understanding of microbiome assembly. Microbial dispersal attenuates with distance, so identifying sources and sinks requires data from microbiomes that are contemporary and near enough for potential microbial transmission. Here, we characterize microbiomes across adjacent terrestrial and aquatic hosts and habitats throughout an entire watershed, showing that the most species-poor microbiomes are partial subsets of the most species-rich and that microbiomes of plants and animals are nested within those of their environments. Furthermore, we show that the host and habitat range of a microbe within a single ecosystem predicts its global distribution, a relationship with implications for global microbial assembly processes. Thus, the tendency for microbes to occupy multiple habitats and unrelated hosts enables persistent microbiomes, even when host populations are disjunct. Our whole-watershed census demonstrates how a nested distribution of microbes, following the trophic hierarchies of hosts, can shape microbial acquisition. 

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