Biology subjects

Davidson, F. A.

Publications and source records attributed to Davidson, F. A..

5 recordsLinked to original sources

bioRxiv2023

Reciprocal sharing of two classes of public goods facilitates Bacillus subtilis biofilm formation

Extracellular proteases are a class of public good that support growth of Bacillus subtilis when nutrients are in a polymeric form. B. subtilis biofilm matrix molecules are another class of public good that are needed for biofilm formation and prone to exploitation. In this study, we investigated the role of extracellular proteases in B. subtilis biofilm formation and explored interactions between different public good producer strains across various conditions. We confirmed that extracellular proteases support biofilm formation even when glutamic acid provides a freely available nitrogen source. Removal of AprE from the NCIB 3610 secretome adversely affects colony biofilm architecture, while sole induction of WprA activity into an otherwise extracellular protease-free strain is sufficient to promote wrinkle development within the colony biofilm. We found that changing the nutrient source used to support growth affected B. subtilis biofilm structure, hydrophobicity, and architecture. We propose that the different phenotypes observed may be due to increased protease dependency for growth when a polymorphic protein presents the sole nitrogen source. We however cannot exclude that the phenotypic changes are due to alternative matrix molecules being made. Co-culture of biofilm matrix and extracellular protease mutants can rescue biofilm structure, yet reliance on extracellular proteases for growth influences population coexistence dynamics. Our findings highlight the intricate interplay between these two classes of public goods, providing insights into microbial social dynamics during biofilm formation across different ecological niches.

microbiology↗

bioRxiv2023

Extracellular proteases are an essential public good supporting Bacillus subtilis growth through exogenous protein degradation

Bacteria encounter polymeric nutrient sources that need to be processed to support growth. Bacillus subtilis is a bacterium known for its adaptability and resilience within the rhizosphere and broader soil environment. Here we explore the role that a suite of extracellular proteases plays in supporting growth of B. subtilis when an extracellular heterologous protein (BSA) provides an abundant, but polymeric, food source. We confirm the essential role of extracellular proteases in this context and note the influence of the polymeric nutrient concentration on the yield of growth, but not on the relative level of extracellular proteases. We demonstrate the collective action of the extracellular proteases in supporting B. subtilis growth and evidence their use as a shared public good. Furthermore, we show that B. subtilis is subjected to a public good dilemma, but only in the context of using a polymeric food source. Using mathematical simulations, we uncover that this dilemma is driven by the relative cost of producing the public good. Collectively, our findings reveal how B. subtilis can survive in environments that vary significantly in terms of immediate nutrient accessibility. This information should inform steps to improve its efficacy as a biofertilizer in agricultural settings.

microbiology↗

bioRxiv2022

Systematic microscopical analysis reveals obligate synergy between extracellular matrix components during Bacillus subtilis colony biofilm development

Single-species bacterial colony biofilms often present recurring morphologies that are thought to be of benefit to the population of cells within and known to be dependent on the self-produced extracellular matrix. However, much remains unknown in terms of the developmental process at the single cell level. Here, we design and implement systematic time-lapse imaging and quantitative analyses of the growth of Bacillus subtilis colony biofilms. We follow development from the initial deposition of founding cells through to the formation of large-scale complex structures. Using the model biofilm strain NCIB 3610, we examine the movement dynamics of the growing biomass and compare with those displayed by a suite of otherwise isogenic matrix-mutant strains. Correspondingly, we assess the impact of an incomplete matrix on biofilm morphologies and sessile growth rate. Our results indicate that radial expansion of colony biofilms results from division of bacteria at the biofilm periphery rather than being driven by swelling due to fluid intake. Moreover, we show that lack of exopolysaccharide production has a negative impact on cell division rate, and the extracellular matrix components act synergistically to give the biomass the structural strength to produce aerial protrusions and agar substrate-deforming ability.

microbiology↗

bioRxiv2021

A theoretical framework for multi-species range expansion in spatially heterogeneous landscapes

Range expansion is the spatial spread of a population into previously unoccupied regions. Understanding range expansion is important for the study and successful manipulation and management of ecosystems, with applications ranging from controlling bacterial biofilm formation in industrial and medical environments to large scale conservation programmes for species undergoing climate-change induced habitat disruption. During range expansion, species typically encounter competitors. Moreover, the environment into which expansion takes place is almost always heterogeneous when considered at the scale of the individual. Despite the ubiquitous nature of these features, the impact of competition and spatial landscape heterogeneities on range expansion remains understudied. In this paper we present a theoretical framework comprising two competing generic species undergoing range expansion and use it to investigate the impact of spatial landscape heterogeneities on range expansion with a particular focus on its effect on competition dynamics. We reveal that the area covered by range expansion during a fixed time interval is highly variable due to the fixed landscape heterogeneities. Moreover, we report significant variability in competitive outcome (relative abundance of a focal species) but determine that this is induced by low initial population densities, independent of landscape heterogeneities. We further show that both area covered by range expansion and competitive outcome can be accurately predicted by a Voronoi tessellation with respect to an appropriate metric, which only requires information on the spatial landscape and the response of each species to that landscape. Finally, we reveal that if species interact antagonistically during range expansion, the dominant mode of competition depends on the initial population density. Antagonistic actions determine competitive outcome if the initial population density is high, but competition for space is the dominant mode of competition if the initial population density is low.

ecology↗

bioRxiv2021

Founder cell configuration drives competitive outcome within colony biofilms

Bacteria typically form dense communities called biofilms, where cells are embedded in a self-produced extracellular matrix. Competitive interactions between strains within the biofilm context are studied due to their potential applications in biological, medical, and industrial systems. Combining mathematical modelling with experimental assays, we reveal that the spatial structure and the competitive dynamics within biofilms are significantly affected by the location and density of founder cells. Using an isogenic pair of Bacillus subtilis strains, we show that the observed spatial structure and relative strain biomass in a mature biofilm can be mapped directly to the locations of founder cells. Moreover, we define a predictor of competitive outcome that accurately forecasts relative abundance of strains based solely on the founder cells access to free space. Consequently, we reveal that variability of competitive outcome in biofilms inoculated at low founder density is a natural consequence of the random positioning of founding cells in the inoculum. Extending our study to non-isogenic strain pairs of B. subtilis, we show that even for strains with different antagonistic strengths, a race for space remains the dominant mode of competition in biofilms inoculated at low founder densities. Our results highlight the importance of spatial dynamics on competitive interactions within biofilms and hence to related applications.

microbiology↗