Biology subjects

Goh, Y.-X.

Publications and source records attributed to Goh, Y.-X..

4 recordsLinked to original sources

bioRxiv2026

Genomic diversification underlies the broad ecological range of Salmonella enterica serotype Typhimurium

Salmonella Typhimurium is a versatile foodborne pathogen with a broad ecological range, making it an ideal model to better understand pathogen adaptations that allow them to infect multiple hosts and persist across environments. Here, we analyzed 595 genomes of S. Typhimurium representing three food animal sources (bovine, swine, and poultry) and one non-food animal source (wild birds). We found that S. Typhimurium from food animal sources generally had a more open pangenome and harbored more antimicrobial resistance genes (ARGs). Notably, swine isolates exhibited the most open pangenome and the highest prevalence of ARGs, patterns that were associated with a greater presence of mobile genetic elements, particularly plasmids. Despite similar core genome sizes, S. Typhimurium from different sources displayed distinct patterns of positive selection in the core genome that varied in frequency and targeted functional categories. In contrast, although accessory genome sizes varied substantially across sources, the frequency of positive selection remained similar. Using machine learning, we identified source-predictive genetic variants, many of which are associated with stress-response functions. These findings suggest that gain and loss of accessory genes and positive selection acting on core genes support differential adaptation in S. Typhimurium, potentially contributing to its broad ecological range.

genomics↗

bioRxiv2026

Motile and non-motile Listeria species adopt distinct genomic and ecological strategies to achieve broad geographic ranges in soil

Broad geographic ranges indicate high ecological versatility and are generally associated with low extinction risk. Motility is not only a physiological feature, but also a core ecological trait for bacteria. However, the genomic foundations underlying the broad geographic ranges of motile and non-motile bacteria remain poorly understood. To address this, we analyzed 141 and 90 genomes of Listeria welshimeri and L. booriae, systematically screened from 1,004 soil samples across the United States, representing widespread motile and non-motile species, respectively. We show that L. welshimeri exhibits restricted phylogeographic structure and a weak distance-decay relationship, suggesting minimal geographic barriers to dispersal. Its high dispersal capacity likely stems from enhanced motility and effective host colonization, evidenced by strong positive selection on flagellar genes and the close relatedness to isolates from wild birds. In contrast, L. booriae displays a regionally endemic distribution and limited dispersal. With a large, open pangenome, L. booriae appears strongly adapted to local environments. This is evidenced by pronounced positive selection on genes involved in inorganic ion, amino acid, and coenzyme transport and metabolism, as well as strong associations with abiotic factors, particularly climate, and accompanying bacterial consortia. In summary, to establish widespread distributions, L. welshimeri tends to rely on movement and colonization of wildlife hosts to facilitate long-distance dispersal, while L. booriae leverages genomic plasticity and metabolic versatility that enable adaptation to diverse environmental conditions. These findings highlight the distinct genomic foundations and ecological strategies that motile and non-motile bacteria use to achieve broad geographic ranges in the environment.

ecology↗

bioRxiv2025

Disentangling the impact of abiotic and biotic environmental factors and dispersal dynamics on bacterial pangenome fluidity

Understanding how pangenomes originate and evolve is crucial for predicting evolutionary trajectories and uncovering ecological interactions of bacterial pathogens. Pangenome fluidity has been attributed to adaptive evolution, yet the underlying ecological drivers for bacterial pathogens persisting in natural reservoirs remain poorly understood. Listeria monocytogenes (Lm), a foodborne pathogen causing fatal listeriosis, serves as an ideal model for investigating the ecological mechanisms underlying pangenome fluidity in bacterial pathogens due to its high evolutionary divergence, broad ecological versatility, and significant public health concern. Through pangenome analysis of 177 Lm isolates representing three evolutionary lineages (I, II, and III) that we isolated from soils across the United States, we found that substantial genome variation was strongly associated with climatic factors (e.g. precipitation and temperature), soil properties (e.g. aluminum, pH, and molybdenum), and bacterial community composition, particularly Nitrospirae, Planctomycetes, Acidobacteria, and Cyanobacteria. These factors exerted selective pressure across many gene functions, with pronounced effects on genes involved in cell envelope synthesis, defense mechanisms, and replication, recombination, and repair. Among Lm lineages occupying varied habitats, distinct pangenome properties were observed. Lineage III exhibited a highly fluid pangenome, which was attributed to local adaptation to nutrient-limited conditions and strong dispersal limitation. In contrast, lineage I maintained a conserved pangenome, likely due to frequent homogenizing dispersal. Consistent with these dispersal patterns, we identified an elevated risk of soil-to-human transmission in lineage I, evidenced by epidemiological links between three soil-derived and 17 clinical isolates. Collectively, this study reveals the pivotal role of environmental selection imposed by both abiotic factors and bacterial communities in governing the adaptive pangenome evolution in bacterial pathogens. It also highlights significant differences in pangenome flexibility, ecological niches, and transmission dynamics across lineages of the same pathogen species, underscoring the need for tailored source tracking strategies. AUTHOR SUMMARYStudying the full set of genes found in different strains of a bacterium (i.e. pangenome) helps us understand how bacterial pathogens develop and adapt to changes in the environment. Here, we focused on Listeria monocytogenes (Lm), a pathogen capable of spreading through food and surviving in diverse environments, to understand how environmental factors and the way that bacteria move across locations can influence the pangenome content in this important bacterium. By analyzing the genomes of 177 Lm strains representing three evolutionary lineages (I, II, and III) collected from soils across the United States, we found that variation in climate, soil chemistry, and surrounding bacteria (e.g., Nitrospirae) was closely linked to genetic differences among strains. These environmental conditions seemed to affect genes that help build the cell envelop, protect the bacteria from harm, and fix damaged DNA. We also observed different levels of genome flexibility across Lm lineages which were found to be related to how they move across different locations. Lineage III showed evidence of barriers to spreading, which may enhance genetic differentiation across populations, leading to a more flexible pangenome. In contrast, lineage I appeared to spread more readily and was epidemiologically linked to human clinical cases, which may facilitate genetic exchange that reduce pangenome diversity. This study shows that both non-living environmental conditions--like precipitation and pH--and nearby groups of bacteria play a big role in shaping how bacterial pathogens change their genes to survive. It also highlights that different subtypes of the same pathogen can have different gene flexibility and spread in different ways, calling for specific biocontrol measures.

genomics↗

bioRxiv2024

Evidence of horizontal gene transfer and environmental selection impacting antibiotic resistance evolution in soil-dwelling Listeria

Soil has been identified as an important reservoir of antibiotic resistance genes (ARGs) and there is a need to understand how corresponding environmental changes influence their emergence, evolution, and spread. As a soil-dwelling bacterial genus containing important pathogens, Listeria, including L. monocytogenes, the causative agent of listeriosis in humans, could serve as a key model for establishing this understanding. Notably, acquired antibiotic resistance among L. monocytogenes isolated from foods and the environment has been observed in some regions over the past decade. Here we characterized ARGs using 594 genomes representing 19 Listeria species that we previously isolated from soils across the United States. Among the five putatively functional ARGs identified, lin, which confers resistance to lincomycin, was the most prevalent, followed by mprF, sul, fosX, and norB. ARGs were found to be predominant in Listeria sensu stricto species and species more closely related to L. monocytogenes tended to harbor more ARGs. Notably, lin, fosX, and norB showed evidence of recent horizontal gene transfer (HGT) across species, likely through transformation as opposed to conjugation and transduction, while mprF and sul appear to have undergone positive selection. In addition, soil properties and surrounding land use were identified as the most important factors associated with ARG richness and genetic divergence, respectively. Using machine learning, we demonstrated that the presence of ARGs can be predicted from environmental variables with good accuracy (mean auROC of 0.76). Collectively, our data suggest that recent HGT and environmental selection played a vital role in the acquisition and diversification of ARGs in the soil environment.

microbiology↗