Biology subjects

Deever, A. N.

Publications and source records attributed to Deever, A. N..

3 recordsLinked to original sources

bioRxiv2026

Human Saliva Induces Acetoin-Dependent Metabolic Adaptation that Promotes Stress Tolerance in Streptococcus mutans

Oral microbes are continually exposed to host-derived saliva, yet its effects on bacterial metabolism and stress adaptation remain incompletely defined. We investigated how saliva supplementation alters the physiology of the caries-associated bacterium Streptococcus mutans using transcriptomics (RNA-Seq), targeted metabolite measurements, specific gene deletions, and transposon sequencing (Tn-Seq). Growth in a chemically defined medium supplemented with pooled saliva altered expression of genes involved in carbohydrate transport, purine biosynthesis, and pyruvate-associated metabolism, including induction of the acetoin dehydrogenase operon. Saliva significantly increased extracellular acetoin accumulation across all S. mutans isolates tested, whereas little accumulation occurred in two commensal streptococcal species examined. Deletion of acetolactate synthase/decarboxylase (alsSaldB) abolished the saliva-associated increase, while deletion of individual acetoin dehydrogenase components (adhC / lplA) enhanced accumulation, supporting the predicted roles of genes in acetoin synthesis and catabolism. Increasing the available carbohydrate concentrations within the media further increased acetoin accumulation, alongside declining terminal culture pH that was significantly lower in cultures supplemented with saliva. Following growth with saliva, S. mutans exhibited approximately 10,000-fold greater survival during a hydrogen peroxide challenge than cells grown without saliva. Mutants within the acetoin pathway retained saliva-associated protection but showed approximately 100-fold lower survival than the wild type. Serial passage of a pooled transposon library identified previously unrecognized saliva-associated fitness determinants, including depletion of mutants carrying insertions in the acetoin dehydrogenase operon. Together, these findings identify acetoin metabolism as a contributor to saliva-associated metabolic remodeling and oxidative stress tolerance in S. mutans and establish saliva as a critical modulator of S. mutans physiology.

microbiology↗

bioRxiv2026

Strain-Level Diversity Decouples Biofilm Architecture, Acidogenic and Aciduric Traits, and Antimicrobial Tolerance in Streptococcus mutans

Streptococcus mutans is a key contributor to dental caries, with its capacity to form structured biofilm microcolonies being a principal component of its cariogenic potential. Yet, most mechanistic studies rely on a limited number of laboratory strains and may not capture the functional diversity present across the species. Here, we characterized a panel of phenotypically and genomically diverse S. mutans isolates to determine how strain background influences biofilm architecture, extracellular matrix accumulation, acid-associated physiology, environmental responsiveness, and antimicrobial susceptibility. Quantitative high-resolution imaging revealed extensive heterogeneity in produced biofilm microcolony size, structure, and matrix composition, demonstrating that biofilm architecture is not a uniform species-level trait. Interestingly, the commonly used reference strain UA159 displayed an intermediate phenotype related to microcolony size and biofilm organization. Human saliva further altered biofilm structure and matrix accumulation in a strain-dependent manner rather than producing a standard species-wide response. Isolates also differed in growth and retained biofilm biomass under acidic conditions, while acid accumulation within mature biofilms varied independently of average microcolony volume, demonstrating that strains that produce larger microcolonies on average were not necessarily associated with greater acid accumulation. Susceptibility to the antiseptics chlorhexidine and cetylpyridinium chloride likewise differed among isolates and could not be predicted from formed biofilm architecture alone. Together, these findings demonstrate that disease-relevant traits commonly attributed to S. mutans are distributed unevenly and only partially coupled across strain backgrounds, with biofilm spatial organization failing to serve as a dominant phenotype linking acid accumulation, acid tolerance, and antimicrobial susceptibility.

microbiology↗

bioRxiv2025

Design, Development and Validation of New Fluorescent Strains for Studying Oral Streptococci

Bacterial strains that are genetically engineered to constitutively produce fluorescent proteins have aided our study of bacterial physiology, biofilm formation, and interspecies interactions. Here, we report on the construction and utilization of new strains that produce the blue fluorescent protein mTagBFP2, the green fluorescent protein sfGFP, and the red fluorescent protein mScarlet-I3 in species Streptococcus gordonii, Streptococcus mutans, and Streptococcus sanguinis. Gene fragments, developed to contain the constitutive promoter Pveg, the fluorescent gene of interest as well as aad9, providing resistance to the antibiotic spectinomycin, were inserted into selected open reading frames on the chromosome that were both transcriptionally silent and whose loss caused no measurable changes in fitness. All strains, except for sfGFP in S. sanguinis, were validated to produce a detectable and specific fluorescent signal. Individual stains, along with extracellular polymeric substances (EPS) within biofilms, were visualized and quantified through either widefield or super-resolution confocal microscopy approaches. Finally, to validate the ability to perform single cell-level analysis using the strains, we imaged and analyzed a triculture mixed-species biofilm of S. gordonii, S. mutans, and S. sanguinis grown with and without addition of human saliva. Quantification of the loss in membrane integrity using a SYTOX dye revealed that all strains had increased loss of membrane integrity with water or human saliva added to the growth media, but the proportion of the population stained by the SYTOX dye varied by species. In all, these fluorescent strains will be a valuable resource for the continued study of oral microbial ecology.

microbiology↗