Biology subjects

Keegstra, J.

Publications and source records attributed to Keegstra, J..

4 recordsLinked to original sources

bioRxiv2026

Widespread attraction of marine bacteria to the macroalgae-derived polysaccharide fucoidan

Fucoidan is the second most abundant polysaccharide in brown macroalgae, contributing up to 50% of the dissolved organic matter released daily from these algae into the ocean, substantially influencing the marine carbon cycle. Due to its complex chemical structure, fucoidan is highly resistant to microbial degradation and accumulates on the surface of macroalgae, where it contributes to regulating their microbiome. Here, we used a range of microfluidic assays to quantify the chemotactic and physiological responses of marine bacteria to fucoidan. Our results reveal that all the strains tested (14 out of 14) are attracted to fucoidan produced by two different species of brown macroalgae. Attraction occurred only at high fucoidan concentrations (0.1 to 1 mg/mL), such as those expected in the immediate vicinity of algal surfaces, whereas low concentrations elicited no response or modest chemorepulsion. Although fucoidan did not support bacterial growth under our experimental conditions, it did not impair the utilization of other carbon sources. Together, these findings suggest that fucoidan gradients can act as chemical cues guiding marine bacteria toward the nutrient-rich microenvironment of macroalgal surfaces, pointing to a potential ecological role of fucoidan in shaping macroalgal microbiota, bacterial behavior, and ultimately carbon cycling in the ocean.

microbiology↗

bioRxiv2023

Interspecies interactions determine growth dynamics of biopolymer degrading populations in microbial communities.

Microbial communities perform essential ecosystem functions such as the remineralization of organic carbon that exists as biopolymers. The first step in mineralization is performed by biopolymer degraders, which harbor enzymes that can break down polymers into constituent oligo- or monomeric forms. The released nutrients not only allow degraders to grow, but also promote growth of cells that either consume the breakdown products, i.e., exploiters, or consume metabolites released by the degraders, i.e., scavengers. It is currently not clear how such remineralizing communities assemble at the microscale - how interactions between the different guilds influence their growth and spatial distribution, and hence the development and dynamics of the community. Here we address this knowledge gap by studying marine microbial communities that grow on the abundant marine biopolymer alginate. We used batch growth assays and microfluidics coupled to time-lapse microscopy to quantitatively investigate growth and spatial distribution of single cells. We found that the presence of exploiters or scavengers alters the spatial distribution of degrader cells. In general, exploiters and scavengers - which we collectively refer to as consumer cells - slowed down the growth of degrader cells. In addition, coexistence with consumers altered the production of the extracellular enzymes that breakdown polymers by degrader cells. Our findings reveal that ecological interactions by non-degrading community members have a profound impact on the functions of microbial communities that remineralize carbon biopolymers in nature. ImportanceBiopolymers are the most abundant source of carbon on the planet and their breakdown by microbial degraders releases metabolic products that allow cross-feeding cells to grow and fuel the assembly of microbial communities. While it is known that the growth of degraders can facilitate growth of downstream cross-feeders in microbial communities, it has remained generally unclear if and how cross-feeders influence growth of degraders. Bridging this knowledge gap is important because degraders primarily drive the remineralization of carbon, a central process in the carbon cycle. We found that the presence cross-feeders can influence the growth of degraders by altering their spatial distribution as well as extracellular breakdown enzyme activity. Our study sheds light on the role of microbial interactions in shaping the rate of carbon remineralization in nature.

microbiology↗

bioRxiv2022

Intercellular collectivity is governed by enzyme secretion strategies in marine polysaccharide degrading bacteria

Polysaccharide breakdown by bacteria requires the activity of enzymes that degrade polymers extracellularly. This generates a localized pool of breakdown products that are accessible to the enzyme producers themselves as well as to other organisms. Marine bacterial taxa often show marked differences in the production and secretion of degradative enzymes that break down polysaccharides. These differences can have profound effects on the pool of diffusible breakdown products and hence on the ecological dynamics. However, the consequences of differences in enzymatic secretions on cellular growth dynamics and interactions are unclear. Here we combine experiments and models to study the growth dynamics of single cells within populations of marine Vibrionaceae strains that grow on the abundant marine polymer alginate, using microfluidics coupled to quantitative single-cell analysis and mathematical modelling. We find that strains that have low extracellular secretions of alginate lyases show stronger aggregative behaviors compared to strains that secrete high levels of enzymes. One plausible reason for this observation is that low secretors require a higher cellular density to achieve maximal growth rates in comparison with high secretors. Our findings indicate that increased aggregation increases intercellular synergy amongst cells of low-secreting strains. By mathematically modelling the impact of the level of degradative enzyme secretion on the rate of oligomer loss to diffusion, we find that enzymatic capability modulates the propensity of cells within clonal populations to cooperate or compete with each other. Our experiments and models demonstrate that marine bacteria display distinct aggregative behaviors and intercellular interactions based on their enzymatic secretion capabilities when growing on polysaccharides.

microbiology↗

bioRxiv2017

Generation And Attenuation Of Variability In A Bacterial Signalling Network Revealed By Single-Cell FRET

We present in vivo single-cell FRET measurements in the Escherichia coli chemotaxis system that reveal pervasive signaling variability, both across cells in isogenic populations and within individual cells over time. We quantify cell-to-cell variability of adaptation, ligand response, as well as steady-state output level, and analyze the role of network design in shaping this diversity from gene expression noise. In the absence of changes in gene expression, we find that single cells demonstrate strong temporal fluctuations. We provide evidence that such signaling noise can arise from at least two sources: (i) stochastic activities of adaptation enzymes, and (ii) receptor-kinase dynamics in the absence of adaptation. We demonstrate that under certain conditions, (ii) can generate giant fluctuations that drive signaling activity of the entire cell into a stochastic two-state switching regime. Our findings underscore the importance of molecular noise, arising not only in gene expression but also in protein networks.

systems biology↗