Biology subjects

Diaz, P. I.

Publications and source records attributed to Diaz, P. I..

7 recordsLinked to original sources

bioRxiv2026

Higher-order metabolic interactions among oral commensals gate pathobiont expansion through succinate-driven pH modulation

Despite advances in defining microbiome shifts associated with inflammatory mucosal diseases, the ecological interactions that constrain or facilitate pathobiont expansion remain poorly understood. Using a six-species synthetic oral microbial community and factorial interaction screening, we identified a higher-order interaction governing the growth of the periodontal pathobiont Porphyromonas gingivalis. The core community member Veillonella parvula was the strongest positive determinant of P. gingivalis growth, but this effect was substantially reduced by the health-associated commensal Actinomyces oris. A. oris-mediated antagonism resulted from extracellular acidification and was enhanced under anaerobic conditions. Genetic dissection of A. oris fermentation revealed that lactate dehydrogenase (ldh1) contributes to anaerobic lactate production, but ldh1 deletion only partially relieved P. gingivalis inhibition. Instead, succinate, produced through a succinate dehydrogenase/fumarate reductase pathway (sdh2), emerged as the principal driver of acidification and P. gingivalis suppression. At high cell densities, however, V. parvula consumed both lactate and succinate, reversing acidification and restoring conditions permissive for P. gingivalis growth. To assess the relevance of these interactions in vivo, we analyzed subgingival microbiome from 1,355 adults, including 555 with detectable P. gingivalis. Among these individuals, P. gingivalis abundance was negatively associated with Actinomyces abundance after adjustment for periodontitis severity, whereas this association was attenuated at high V. parvula abundance, consistent with the interaction observed in vitro. Together, these findings identify succinate as a previously unrecognized mediator of interbacterial antagonism and reveal how higher-order metabolic interactions among oral commensals regulate pathobiont expansion through pH modulation, with protective effects shaped by oxygen availability and metabolic cross-feeding.

microbiology↗

bioRxiv2026

A population-scale landscape of the subgingival microbiome reveals divergent routes to periodontal dysbiosis

Periodontitis is an archetypical mucosal inflammatory disease in which microbiome dysbiosis at the tooth-epithelial interface interacts with host genetic and behavioral risk factors to drive immune-mediated tissue destruction. Although subgingival microbiome compositional shifts are thought to parallel disease severity, microbiome variation at the population-level and its relationship to periodontal clinical phenotypes and disease-modifying factors remain poorly defined. Here, we use unsupervised manifold learning to map the compositional landscape of the subgingival microbiome in 1,355 adults spanning periodontal health to severe periodontitis. We identified eight latent microbiome states organized along a branching continuum from eubiosis to dysbiosis. An intermediate microbial configuration marked ecological destabilization and bifurcation into two distinct periodontitis-associated dysbiotic trajectories, distinguished by links to gingival inflammation and smoking. Although the microbiome trajectories broadly tracked periodontal destruction, a minority of individuals showed discordant microbiome-clinical phenotypes, with some individuals with periodontitis retaining otherwise eubiotic microbiomes enriched for low-abundance pathobionts, while some cases of health or mild disease had highly dysbiotic communities, suggesting distinct host susceptibility. Together, these findings define a population-scale ecological landscape of the subgingival microbiome, reveal divergent trajectories to periodontal dysbiosis, and highlight heterogeneity in the relationship between microbial community structure and clinical disease expression.

microbiology↗

bioRxiv2026

Pervasive integrative and conjugative elements shape Porphyromonas gingivalis gene repertoires

BackgroundPorphyromonas gingivalis (Pg) is an oral pathobiont that contributes to periodontal disease and has been associated with systemic health conditions. Although Pg is recognized as exhibiting extensive strain-level genomic diversity and recombination, the extent to which mobile elements contribute to this variation, and their relevance to its fitness and virulence, remain incompletely understood. Our recent study of the Pg pangenome revealed diverse accessory defense-associated genes, raising the question of whether these are carried by unrecognized mobile genetic elements (MGEs). Integrative and conjugative elements (ICEs) are large autonomous mobile elements that often encode genes for proteins beneficial to their bacterial hosts, including defense systems that protect against phage infection. To date, only one ICE, CTnPg1, has been described in Pg. ResultsHere, we developed a bioinformatic approach integrating ICE prediction and curation, hallmark-gene detection, and genomic-context analysis, to investigate ICEs in Pg. We discovered that ICEs are pervasive in Pg genomes, with >90% of genomes harboring at least one ICE. We found that these elements comprise at least five distinct groups, two of which dominate and frequently co-occur in Pg genomes, inserting into distinct characteristic insertion sites. Using marker-gene analysis of enrichment-culture mini-metagenomes from subjects with periodontal disease we detected representatives of these dominant Pg ICE groups, as well as others, in recent clinical samples. We found that anti-defense and defense genes are common in Pg ICEs, and that these elements commonly encode biosynthetic gene clusters, including for menaquinone synthesis and predicted ribosomally synthesized and post-translationally modified peptides (RiPPs). In contrast to the extensive CRISPR-Cas defense targeting we observed for Pg phages, we detected no exact matches between ICE sequences and Pg CRISPR spacers. ConclusionThis work establishes that ICEs are pervasive contributors to Pgs pangenome and unique strain-level gene repertoires. Their distinct cargo profiles suggest that ICEs likely impact the virulence and ecology of Pg through the introduction and spread of advantageous traits, including expansion of Pgs biosynthetic capacity and resistance to phage infection. This work provides a curated framework for investigating ICE diversity in Pg and establishes a foundation for expanded experimental studies of their host ranges and roles in shaping Pgs interactions with phages, other microbes, and the human host.

microbiology↗

bioRxiv2026

Chemotherapy-Induced Oral Mucosal Injury Is Defined by p53 Activation, Cell Cycle Arrest and Diverse Epithelial Progenitor Dynamics

Chemotherapy-induced oral mucositis is a common and debilitating complication, yet the mechanisms underlying oral mucosa injury and repair remain poorly defined. Using a mouse model of 5-fluorouracil (5-FU)-induced mucositis, we define gene networks and oral mucosal cellular landscape dynamics in response to chemotoxic stress. We show that 5-FU-induced epithelial atrophy is driven primarily by cell cycle arrest rather than apoptosis, despite concurrent activation of p53-dependent transcriptional programs linked to both cell fates within individual cells. Relative to intestine, the recovering oral mucosa exhibits a more effective cell cycle checkpoint response and uniquely undergoes metabolic reprogramming toward lipid oxidation. Single-cell RNA sequencing revealed putative epithelial progenitor populations with distinct responses to chemotherapy, including chemoresistant cells with a p53- and AP-1 complex gene signature, reminiscent of lung transitional cell states. These findings define diverse progenitor dynamics and p53-driven responses as key determinants of oral mucosal injury and repair following chemotherapy.

cell biology↗

bioRxiv2025

Ecological and Stochastic Determinants of the Growth and Persistence of the Oral Pathogen Porphyromonas gingivalis

Population density plays a critical role in microbial fitness, yet its influence on pathogen colonization and persistence remains incompletely understood. Porphyromonas gingivalis (Pg) exhibits Allee-type growth, requiring a quorum threshold to replicate, yet is frequently detected at low abundance in vivo. We integrate quantitative growth experiments with mathematical modeling to identify ecological and stochastic determinants of Pg persistence. A cubic Allee-effect model quantifies a quorum threshold below which populations collapse, while conditioned medium from Veillonella parvula (Vp) lowers this threshold, indicating early-colonizer facilitation. Stochastic extensions and Fokker-Planck analysis show that microenvironmental noise enables escapes across the Allee barrier, consistent with long-term subthreshold experiments yielding a stationary, powerlaw-like distribution and under-threshold survival. Pg-Vp co-cultures further demonstrate replicate rescue outcomes for subcritical inocula. Critically, Vp reliably saturates to capacity, constraining terminal phases within the experimental horizon to coexistence (Pg persists with Vp at capacity) or Pg extinction. A two-species replicator model maps these outcomes onto a ({beta}, {gamma}) plane, restricting accessible regions once Vp is established and suggesting interventions that reduce facilitation or variability to restore eubiosis and limit Pg-associated inflammation.

systems biology↗

bioRxiv2025

The Impact of Serum on a Complex Synthetic Community Model of the Subgingival Microbiome

Despite rapid advances in characterizing the human microbiome, the ecological pressures shaping its transitions from healthy to diseased states remain poorly resolved. This is particularly true for periodontitis, a slow-progressing chronic inflammatory disease associated with well-defined shifts in the subgingival microbiome. Here, we report the development of a complex synthetic community model of the subgingival microbiome, designed for systematic interrogation of ecological factors that drive community restructuring. The model includes 22 prevalent and abundant subgingival species maintained in mucin-rich medium under microaerophilic, continuous culture conditions, in a chemostat. Using this system, we interrogated the impact of serum, as a surrogate for the inflammatory exudate, on community structure and function. Through integrated 16S rRNA gene sequencing, metatranscriptomics, and metabolomics, we found that serum was not required for a community with a periodontitis-like configuration to establish, but its presence intensified features of dysbiosis. Serum increased total biomass, promoted polymicrobial aggregate formation, promoted nitrogen and protein metabolism thereby modifying the environmental pH towards alkalinity, and introduced nitrosative stress. Serum also modified the community metatranscriptome in ways that paralleled microbiome activities in human periodontitis. Serum, however, decreased community diversity by disproportionally conferring a competitive advantage to the pathogen Porphyromonas gingivalis. This synthetic community model has revealed serum as a key nutritional pressure that modulates subgingival microbiome ecology and may perpetuate dysbiosis.

microbiology↗

bioRxiv2020

A cross-species interaction with a symbiotic commensal enables cell-density-dependent growth and in vivo virulence of an oral pathogen

Recent studies describe in detail the shifts in composition of human-associated polymicrobial communities from health to disease. However, the specific processes that drive the colonization and overgrowth of pathogens within these communities remain incompletely understood. We used in vitro culture systems and a disease-relevant mouse model to show that population size, which determines the availability of an endogenous diffusible small molecule, limits the growth, colonization, and in vivo virulence of the human oral pathogen Porphyromonas gingivalis. This bacterial pathogen overcomes the requirement for an endogenous cue by utilizing a cell-density dependent, growth-promoting, soluble molecule provided by the symbiotic early colonizer Veillonella parvula, but not produced by other commensals tested. Our work shows that exchange of cell-density-dependent diffusible cues between specific early and late colonizing species in a polymicrobial community drives microbial successions, pathogen colonization and disease development, representing a target process for manipulation of the microbiome towards the healthy state.

microbiology↗