Biology subjects

Wale, N.

Publications and source records attributed to Wale, N..

4 recordsLinked to original sources

bioRxiv2024

Imaging flow cytometry enables label-free cell sorting of morphological variants from unculturable bacterial populations.

Bacterial populations often display remarkable morphological heterogeneity. Flow cytometric cell sorting (often called FACS) is an important tool for understanding this diversity. FACs allows researchers to obtain pure samples of each morphological variant (or morphotype) that is present within a mixed population of cells and thus permits each morphotype to be phenotyped. In FACS, cells are first labeled with fluorescent markers such as antibodies or transgenic constructs, and then separated out based on their possession of these labels. However, since the development of fluorescent labels requires a priori knowledge of bacterial biology, it is often impossible to apply FACS to understudied and/or unculturable bacteria. This challenge has limited our capacity to investigate the biology of bacterial size and shape in all but a small, largely culturable subset of bacterial taxa. Here, we present an innovative strategy that permits label-free cell sorting of bacterial morphotypes, using an unculturable, pleiomorphic pathogen (Pasteuria ramosa) as a model bacterium. We show that imaging flow cytometry (IFC) can be used to systematically identify light-scattering and autofluorescence "signatures" of bacterial morphotypes, on which basis cell sorting can be conducted. Critically, our IFC-enabled cell sorting strategy yields samples of sufficient purity (>90%) for common downstream analyses e.g., "-omics" analyses. Our work represents an innovative application of IFC and provides an economical, widely applicable solution to a central problem in the study of bacterial diversity. ImportanceBacteria come in many different shapes and sizes. Why this morphological variation exists is a longstanding question in microbiology, but it remains difficult to answer. To phenotype different morphological variants (morphotypes) within a bacterial population, we need to separate them from one another. This is normally achieved using flow cytometric cell-sorting, whereby morphotypes are labelled with fluorescent antibodies and separated on the basis of their differential fluorescence. Unfortunately, it is difficult to develop fluorescent-labels specific to unculturable or poorly studied bacteria because of the limited availability of appropriate molecular tools. Here, we demonstrate that imaging flow cytometry can be used to design and validate label-free cell sorting strategies. Recently, there has been a resurgence of interest in bacterial morphological diversity and a call to expand its study across the tree of life. Our work will help microbiologists to answer this call.

microbiology↗

bioRxiv2024

Red blood cell dynamics during malaria infection violate the assumptions of mathematical models of infection dynamics

For decades, mathematical models have been used to understand the course and outcome of malaria infections (i.e., infection dynamics) and the evolutionary dynamics of the parasites that cause them. The extent to which this conclusion holds will in part depend on model assumptions about the host-mediated processes that regulate RBC availability, i.e., removal (clearance) of uninfected RBCs and supply of RBCs. Diverse mathematical functions have been used to describe host-mediated RBC supply and clearance in rodent malaria infections; however, the extent to which these functions adequately capture the dynamics of these processes has not been quantitatively interrogated, as in vivo data on these processes has been lacking. Here, we use a unique dataset, comprising time-series measurements of erythrocyte (i.e., mature RBC) and reticulocyte (i.e., newly supplied RBC) densities during Plasmodium chabaudi malaria infection, and a quantitative data-transformation scheme to elucidate whether RBC dynamics conform to common model assumptions. We found that RBC supply and clearance dynamics are not well described by mathematical functions commonly used to model these processes. Indeed, our results suggest said dynamics are not well described by a single-valued function at all. Furthermore, the temporal dynamics of both processes vary with parasite growth rate in a manner again not captured by existing models. Together, these finding suggest that new model formulations are required if we are to explain and ultimately predict the within-host population dynamics and evolution of malaria parasites.

microbiology↗

bioRxiv2023

Virulence and transmission biology of the widespread, ecologically important pathogen of zooplankton, Spirobacillus cienkowskii

Spirobacillus cienkowskii (Spirobacillus, hereafter) is a widely distributed bacterial pathogen that has significant impacts on the population dynamics of zooplankton (Daphnia spp.), particularly in months when Daphnia are asexually reproducing. Yet little is known about Spirobacillus virulence, transmission mode and dynamics. As a result, we cannot explain the dynamics of Spirobacillus epidemics in nature or use Spirobacillus as a model pathogen, despite Daphnias tractability as a model-host. Here, we work to fill these knowledge gaps experimentally. We found that Spirobacillus is among the most virulent of Daphnia pathogens, killing its host within a week and reducing host fecundity. We further found that Spirobacillus did not transmit horizontally among hosts unless the host died or was destroyed (i.e., it is an "obligate killer"). In experiments aimed at quantifying the dynamics of horizontal transmission among asexually reproducing Daphnia, we demonstrated that Spirobacillus transmits poorly in the laboratory. In mesocosms, Spirobacillus failed to generate epidemics; in experiments wherein individual Daphnia were exposed, Spirobacillus transmission success was low. In the (limited) set of conditions we considered, Spirobacillus transmission success did not change with host density or pathogen dose and declined following environmental incubation. Lastly, we conducted a field survey of Spirobacillus prevalence within egg-cases (ephippia) made by sexually reproducing Daphnia. We found Spirobacillus DNA in [~]40% of ephippia, suggesting that, in addition to transmitting horizontally among asexually reproducing Daphnia, Spirobacillus may transmit vertically from sexually reproducing Daphnia. Our work fills critical gaps in the biology of Spirobacillus and illuminates new hypotheses vis-a-vis its life-history. ImportanceSpirobacillus cienkowskii is a bacterial pathogen of zooplankton, first described in the 19th Century and recently placed in a new family of bacteria, the Silvanigrellaceae. Spirobacillus causes epidemics in lake zooplankton populations and increases the probability that zooplankton will be eaten by predators. However, little is known about how Spirobacillus transmits among hosts, its impact on host survival and reproduction (i.e., how virulent it is) in laboratory conditions and what role virulence plays in Spirobacillus life cycle. Here, we experimentally quantified Spirobacillus virulence and showed that Spirobacillus must kill its host to transmit horizontally. We also found evidence that Spirobacillus may transmit vertically via Daphnias seed-like egg cases. Our work will help scientists to (i) understand Spirobacillus epidemics, (ii) use Spirobacillus as a model pathogen for the study of host-parasite interactions and (iii) better understand the unusual group of bacteria to which Spirobacillus belongs.

microbiology↗

bioRxiv2019

Breaking down defenses: Quantitative analysis of malaria infection dynamics reveals distinct immune defense strategies

Hosts defend themselves against pathogens by mounting an immune response. Fully understanding the immune response as a driver of host disease and pathogen evolution requires a quantitative account of its impact on parasite population dynamics. Here, we use a data-driven modeling approach to quantify the birth and death processes underlying the dynamics of infections of the rodent malaria parasite, Plasmodium chabaudi, and the red blood cells (RBCs) it targets. We decompose the immune response into three components, each with a distinct effect on parasite and RBC vital rates, and quantify the relative contribution of each component to host disease and parasite density. Our analysis suggests that these components are deployed in a coordinated fashion to realize distinct resource-directed defense strategies that complement the killing of parasitized cells. Early in the infection, the host deploys a strategy reminiscent of siege and scorched-earth tactics, in which it both restricts the supply of RBCs and destroys them. Late in the infection, a juvenilization strategy, in which turnover of RBCs is accelerated, allows the host to recover from anemia while holding parasite proliferation at bay. By quantifying the impact of immunity on both parasite fitness and host disease, we reveal that phenomena often interpreted as immunopathology may in fact be beneficial to the host. Finally, we show that, across mice, the components of the host response are consistently related to each other, even when infections take qualitatively different trajectories. This suggests the existence of simple rules that govern the immune systems deployment.

ecology↗