Biology subjects

Ong, C. T.

Publications and source records attributed to Ong, C. T..

5 recordsLinked to original sources

bioRxiv2026

Metagenomic prediction of methane emissions in sheep using single- and multi-matrix BLUP models with taxonomic and functional microbial features

BackgroundEnteric methane emissions from ruminant livestock represent a major greenhouse gas contributor, yet identification of high- and low-emitting ruminants remains expensive and logistically challenging for agricultural methane mitigation strategies. Ruminal microbial profiles derived from long-read sequencing technology provide a potential proxy to predict methane production. The optimal bioinformatic pipelines for processing long-read metagenomic data to perform methane predictions have yet to be determined. Here we evaluated how different metagenomic analysis pipelines affect methane predictive model accuracy in grazing sheep. ResultsWe applied three bioinformatic pipelines to characterize the taxonomic and functional features of rumen microbiomes from 396 sheep. Functional abundance features were annotated from Clusters of Orthologous Genes (COG) or Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. The single-matrix model using COG features achieved the highest microbiability (m2 = 0.942: proportion of variance component explained by microbial features) and predictive accuracy (5-fold cross validation r = 0.609: Pearsons correlation between predicted and observed values). Both functional features outperformed all taxonomic features across all three pipelines in predictive accuracy. The multi-matrix models combined functional and taxonomic features slightly improved methane predictive accuracy across both 5-fold cross-validation and leave-one-day-out validation compared to the models using functional features alone. ConclusionsThese findings demonstrate the potential advantages of using long-read metagenomic data to predict enteric methane emissions in ruminants. COG-based functional features achieved the highest predictive accuracy among all feature types, suggesting that functional annotation of existing long-read sequences is sufficient for accurate methane prediction without requiring complementary taxonomic data.

genomics↗

bioRxiv2026

Epigenetic Patterns of Xylanibacter ruminicola in Bovine Rumen Across Seasons and Pregnancy

Ruminants obtain nutrients through the microbial fermentation of plant material in the rumen. Xylanibacter ruminicola is a highly abundant bacterial species in the rumen. During fermentation, X. ruminicola utilizes diverse carbohydrates from plant materials to synthesize propionate, a volatile fatty acid providing energy to ruminants. However, variation in pasture quality (e.g, nutrient and fibre content) across seasons and host pregnancy status can alter the rumen microenvironment, potentially affecting microbial activity. Bacteria in culture display distinct methylation (a reversible epigenetic modification capable of gene regulation) changes in response to the growth environment. We hypothesized that the changes to the rumen environment would affect the DNA methylation patterns within the X. ruminicola genome. Rumen fluid from 37 female Brahman cattle (17 pregnant) were sampled across four seasons. DNA methylation profiles (N6-methyladenine, N4-methylcytosine, and 5-methylcytosine) of X. ruminicola across seasons (varying pasture quality) and pregnancy statuses characterized using Oxford Nanopore sequencing. After correcting for relative abundance, DNA methylation levels within the coding DNA sequences of several X. ruminicola genes differed between seasons and pregnancy status. Most of these genes were classified as ExbD/TolR family proteins and related to the protein transport process. Our study demonstrates that the DNA methylation profiles of rumen X. ruminicola genes vary with host environment factors. These results provide insight into the role of bacterial DNA methylation in mediating interactions between bacteria and their environments. Lay SummaryRuminants rely on rumen microbes to convert plants into nutrients. Xylanibacter ruminicola is a bacterial species in the rumen that produces nutrients for ruminants during plant fermentation. Changes in pasture quality and host pregnancy status can influence the activity of X. ruminicola, as reflected in the DNA methylation profile across its genome. DNA methylation is a reversible DNA modification that can affect gene activity and help bacterial adaptation to changing environments. Rumen fluid from 37 female Brahman cattle (17 pregnant) across four seasons were used to evaluate the pasture quality and host pregnancy effects on the DNA methylation profile of X. ruminicola. The relative abundances of X. ruminicola were influenced by pasture quality, but not by host pregnancy. However, host pregnancy status and changes in pasture quality influenced the DNA methylation signatures of X. ruminicola. Genes with DNA methylation changes were associated with the protein transport process. These findings suggest that the DNA methylation profiles of rumen X. ruminicola vary with host environment factors. Teaser TextThis study demonstrates that the DNA methylation profiles of rumen Xylanibacter ruminicola vary with host environment factors. These findings provide insight into the role of bacterial DNA methylation in mediating interactions between rumen bacteria and their environment.

microbiology↗

bioRxiv2026

DNA methylation in Escherichia coli changes in response to growth conditions

Bacteria require rapid adaptation under fluctuating environmental conditions. Commonly recognized global regulators enable bacteria to respond promptly to external changes, though they are either restricted to specific bacterial taxonomies or physiological statuses, suggesting that additional regulators are required for adaptation. DNA methylation is a reversible modification affecting bacterial gene regulation. However, conventional methods can only detect one DNA methylation form each round, leaving the understanding of DNA methylation in bacterial adaptation mostly unknown. This study aimed to identify genome-wide DNA methylation variation (N6-methyladenine, N4-methylcytosine, and 5-methylcytosine) in Escherichia coli under different culture conditions using Oxford Nanopore sequencing. DNA samples from six conditions (normal, low oxygen, low pH, high temperature, high salt, and recovery after low pH exposure) during the exponential and stationary phases were extracted. When culture conditions were compared to the normal condition, E. coli exhibited more differentially methylated sites during the exponential phase than in the stationary phase. During the exponential phase, the genes differentially methylated in all conditions were involved in cellular activities, such as cellular and metabolic processes. During the stationary phase, universally differentially methylated genes were associated with oxidation responses. Subsequent analysis found that although DNA methylation analysis was affected by batch effects, some genes (e.g. rpoS) showed consistently differential methylation across datasets. Our findings suggest that the E. coli DNA methylation profile was affected by growth phases and conditions, and DNA methylation profiling by Oxford Nanopore sequencing could be a potential approach for gene activity estimation in environmental samples. ImportanceBacterial DNA methylation is a reversible genetic modification affecting gene regulation, enabling rapid adaptation. Three major forms in bacteria are N6-methyladenine, N4-methylcytosine, and 5-methylcytosine. Using Oxford Nanopore sequencing, we characterized genome-wide variation in these methylation types in Escherichia coli under six conditions (normal, low oxygen, low pH, high temperature, high salt, and recovery after low pH exposure). DNA methylation signatures in E. coli varied with growth conditions. Using the normal condition as a baseline, E. coli during the exponential phase exhibited more differentially methylated genomic loci under stress conditions compared to the stationary phase. Under stress conditions, genes with differential methylation were associated with cellular processes or oxidative responses, depending on the growth phase. Our findings reveal that the DNA methylation signature in E. coli was affected by growth phases and conditions, and Oxford Nanopore-based DNA methylation profiling could be a potential approach for gene activity estimation in environmental samples.

microbiology↗

bioRxiv2026

Short communication: Oral microbiome as a potential proxy for grazing livestock methane emissions

Enteric methane emissions from ruminant livestock contribute to global warming, creating an urgent need for effective mitigation strategies that do not compromise animal productivity and welfare. Methanogenic archaea within the rumen microbiome drive enteric methane emissions. However, large-scale rumen-fluid sampling in commercial production systems is impractical, due to its invasive nature and the associated logistical challenges. This study hypothesised that rumination enables the capture of rumen microbial signals within the oral cavity and using oral microbiome profiles to provide a practical, non-invasive alternative method for proxy methane phenotyping in commercial production systems. To test the hypothesis, we estimated the oral microbiability, defined as the proportion of phenotypic variance in methane emissions explained by oral microbiome variation. Samples were collected from 209 animals across two trials in Queensland, Australia. Oral microbiome samples were obtained from all animals, with paired rumen samples in one trial, and methane emissions were measured using either the sulphur hexafluoride (SF6) tracer technique or the GreenFeed system. Microbial features were characterised using taxonomic and functional annotations, and microbiability was estimated using mixed linear models incorporating microbiome-based relationship matrices. Although the small sample size limited strong conclusions, the oral microbiability estimates reported in this study were comparable to those derived from rumen samples. Functional microbial profiles generally explained a greater proportion of methane variation than taxonomic profiles, suggesting that microbial function is more closely linked to methane production than community composition alone. However, these differences were not statistically significant due to large standard errors. These findings suggest that oral microbiome sampling potentially provides a practical, minimally invasive, scalable proxy method for methane emissions of individual cattle in grazing systems, where direct methane gas measurements are labour-intensive and difficult to implement. Integrating oral microbiome profiles in the existing breeding model with the host genetics, weight and environmental factors could provide a promising pathway for enabling selection for low emissions and advancing reduced emissions livestock farming under real-world production conditions. Lay summaryCattle produce methane as part of their normal digestion and this contributes to climate change. Reducing methane emission in grazing livestock systems is therefore important. However, measuring methane from individual grazing animals is difficult, costly, and often impractical under commercial conditions. The rumen microbiome has been used as a proxy for estimating methane emissions, but collecting rumen samples is invasive and impractical for large-scale use. Because rumination transfers material from the rumen to the mouth, we investigated whether microbes found in cattle mouths could also be used to estimate how much methane an individual animal produced. We suggest that mouth-swab sampling method can be an alternative to rumen fluid sampling because it was less invasive, relatively quick and practically applicable in commercial conditions. Importantly, the microbiome explained a meaningful proportion of the between-animal variation for methane emission. This suggests that collection of mouth swabs is a potentially scalable alternative proxy method to identify cattle that naturally produce less methane. Overall, our findings support the potential use of oral ruminant microbial information to improve breeding and management strategies aimed at reducing methane emissions while maintaining productive livestock systems. Teaser TextThis study demonstrates that collecting oral swabs from the mouths of grazing beef cattle could provide a scalable method to estimate individual methane emissions in commercial production systems, offering a practical alternative to invasive rumen sampling and complex gas measurement systems. These findings support the development of scalable breeding and management strategies for methane mitigation in large-scale livestock production systems.

microbiology↗

bioRxiv2022

The role of Staphylococcus agnetis and Staphylococcus hyicus in the pathogenesis of buffalo fly skin lesions in cattle

Buffalo flies (Haematobia irritans exigua) are hematophagous ectoparasites of cattle causing production and welfare impacts in northern Australian herds. Skin lesions associated with buffalo fly infestation and Stephanofilaria nematode infection are manifested as focal dermatitis or ulcerated areas most commonly on the medial canthus of the eye, along the lateral and ventral neck and on the abdomen of cattle. For closely related horn flies (Haematobia irritans irritans), Staphylococcus aureus have been suggested as a contributing factor in the development of lesions. To investigate the potential role of bacterial infection in the pathogenesis of buffalo fly lesions, swabs were taken from lesions and normal skin, and bacteria were also isolated from surface washings of buffalo flies and surface-sterilised homogenized flies. Bacterial identification was conducted by MALDI-TOF, strain typing by rep-PCR and DNA sequencing to determine species similarity and virulence factors. Of 49 bacterial isolates collected from lesions, 37 were identified as Staphylococcus agnetis and 12 as Staphylococcus hyicus, whereas from normal skin four isolates were S. hyicus and one was Staphylococcus sciuri. Of the Staphylococcus isolates isolated from buffalo flies, five were identified as S. agnetis and three as S. hyicus. Fifty percent of the buffalo fly isolates had rep-PCR genotypic patterns identical to the lesion isolates. Genome sequencing of 16 S. agnetis and four S. hyicus isolates revealed closely similar virulence factor profiles, with all isolates possessing exfoliative toxin A and C genes. The findings from this study suggest the involvement of S. agnetis and S. hyicus in buffalo fly lesion pathogenesis. This should be taken into account in the development of effective treatment and control strategies for lesions.

microbiology↗