Biology subjects

Swink, C.

Publications and source records attributed to Swink, C..

4 recordsLinked to original sources

bioRxiv2026

Oxidative stress reshapes diatom-microbiome interactions by shifting benefits from mutualistic to opportunistic bacteria

The roles of reactive oxygen species (ROS) as signaling molecules and inhibitors of phytoplankton growth are well documented. While phytoplankton physiological mechanisms for ROS detoxification are well characterized, the role of heterotrophic bacterial partners in ROS alleviation and outcomes for these bacteria remain poorly understood. Here, we examined how extracellular hydrogen peroxide (H2O2) shapes nutrient exchange between the diatom Phaeodactylum tricornutum and two phycosphere bacteria. From an initial screen of 20 bacteria, we identified a "helper" (Muricauda sp.) that enabled P. tricornutum to survive acute H2O2 stress and a "non-helper" (Algoriphagus sp.) that did not. Using nanoscale secondary ion mass spectrometry (nanoSIMS), we tracked diatom-derived carbon and nitrogen (13C and 15N) transfer to each bacterial partner under ROS stress. Oxidative stress disrupted diatom metabolism and altered nutrient transfer: diatom-derived carbon and nitrogen incorporation was significantly reduced in the helper but increased in the non-helper under H2O2 stress. Growth assays revealed that the helper preferentially utilized exudates from healthy, intact hosts, whereas the non-helper did not grow on exudates but thrived on lysates from damaged or lysed cells. Together, these findings indicate the helper was better adapted to accessing resources from living hosts, while the non-helper relied on nutrients released through ROS-induced host damage. Our results highlight oxidative stress as a key driver of algal-bacterial interactions and suggest that bacterial resource-acquisition strategy underlies host protection: bacteria utilizing healthy-host exudates are more likely to protect hosts from oxidative stress, while those benefiting from host damage are not, despite retaining ROS detoxification capacity.

microbiology↗

bioRxiv2024

Spatially structured competition and cooperation alters algal carbon flow to bacteria

Microbial communities regulate the transformations of carbon in aquatic systems through metabolic interactions and food-web dynamics that can alter the balance of photosynthesis and respiration. Direct competition for resources is thought to drive microbial community assembly in algal systems, but other interaction modes that may shape communities are more challenging to isolate. Through untargeted metabolomics and metabolic modeling, we predicted the degree of resource competition between bacterial pairs when growing on model diatom Phaeodactylum tricornutum-derived substrates. In a subsequent sequential media experiment, we found that pairwise interactions were consistently more cooperative than predicted based on resource competition alone, indicating an unexpected role for cooperation in algal carbon processing. To link this directly to algal carbon fate, we chose a representative cooperative and competitive influencer isolate and a model recipient and applied single-cell isotope tracing in a custom porous microplate cultivation system. In the presence of live algae, the recipient drew down more algal carbon in the presence of the cooperative influencer compared to the competitive influencer, supporting the sequential experiment results. We also found that total carbon assimilation into bacterial biomass, integrated over influencer and recipient, was significantly higher for the cooperative interaction. Our findings support the notion that non-competitive interactions are critical for predicting algal carbon fate. Significance StatementMicrobial interactions have widely been studied in the context of host resources but testing and measuring direct interactions in a lab has been particularly challenging. By combining untargeted metabolomics, sequential/(co-)culture, and metabolic modeling, we demonstrate that the presence of an unexpected interaction mode in a live system and show how it impacts the flow of host-derived resources. This top-down approach can help identify novel bacterial interactions that play a crucial role in microbial community-host ecosystems, which may have an impact in holobiont phenotypes including alga, fungal, or plant systems.

microbiology↗

bioRxiv2024

Seasonal niche overlap of diverse facultative antagonistic bacteria of diatoms in a productive coastal ecosystem

Biotic interactions between microbes underpin marine ecosystem health, governing the flux of carbon and other nutrients in the ocean. However, studying aquatic microbial interactions is challenging. Model systems can provide in depth understanding of the mechanisms driving such associations. Yet, insights of the prevalence and co-occurrence dynamics of laboratory model systems in natural ecosystems remain limited. By leveraging 16S and 18S metabarcoding combined with phylogenetic analysis, we assessed the environmental presence of facultative bacterial pathogens of one of the most globally abundant phytoplankton groups, the diatoms. Sampling microbial assemblages in a productive coastal ecosystem over the course of an annual cycle, we detected multiple algicidal bacteria that frequently exhibited overlapping co-occurrences. Together, these bacteria positively correlated with members of the potentially toxic genus Pseudo-nitzchia, as well as temperature. Our study indicates that antagonistic bacteria occupy shared temporal niches and demonstrates the need to consider their cumulative impacts on diatom population health, including in future ocean conditions.

ecology↗

bioRxiv2022

Dynamic Phaeodactylum tricornutum Exometabolites Shape Surrounding Bacterial Communities

The roles of exometabolites in mediating algal-bacterial interactions and regulating microbial community composition are not well understood. Here, we identified specific exometabolites from the model diatom Phaeodactylum tricornutum affecting abundance of specific bacterial taxa in isolation and in a community setting. We examined the response of a P. tricornutum-adapted enrichment community and found that both algal exudates and algal presence drove similar changes in community composition compared to controls. Using LC-MS/MS, we identified 50 metabolites produced by axenic P. tricornutum and found that different exometabolites accumulated during different algal growth phases. Profiling growth of 12 bacterial isolates representative of the enrichment community uncovered two algal exometabolites (out of 12 tested) which supported growth of a subset of isolates as a primary carbon source. We compared enrichment community response with and without the addition of two contrasting metabolites: 4-hydroxybenzoic acid, which supported isolate growth, and lumichrome, which did not. Exogenous metabolite additions did promote increased abundances of taxa that were able to utilize the metabolite in the isolate study, but also revealed the importance of factors relating to algal presence in regulating community composition. Collectively, this work demonstrates the influence of specific algal exometabolites in driving microbial community composition.

microbiology↗