Biology subjects

Croze, O. A.

Publications and source records attributed to Croze, O. A..

4 recordsLinked to original sources

bioRxiv2025

Chemokinesis by a microbial predator

Regulated motility is vital for many cells--both for unicellular microbes and for cells within multicellular bodies. Different conditions require different rates and directions of movement. For the microbial predator Capsaspora owczarzaki, its motility is likely essential for predation. This organism has been shown to prey on diverse organisms, including the schistosome parasites that co-reside with it in Biomphalaria glabrata snails. Capsaspora is also an evolutionary model for the unicellular ancestor of animals. This phylogenic placement makes Capsasporas motility an attractive target for understanding the evolution of motility in animal cells. Until now, little was known of how Capsaspora regulates it rate and direction of motility. Here we found that it exhibits chemokinesis (increased movement in response to chemical factors) in response to proteins released from prey cells. Chemokinesis also occurs in response to pure proteins--including bovine serum albumin. We found that this chemokinesis behavior is dependent on Capsaspora cell density, which suggests that the regulated motility is a cooperative behavior (possibly to improve cooperative feeding). We developed a mathematical model of Capsaspora motility and found that chemokinesis alone does not benefit Capsaspora predation. However, when coupled with chemotaxis (directional motility along a chemical gradient toward prey), chemokinesis may improve predation. Finally, we quantitatively analyzed Capsasporas previously reported chemotaxis behavior. These findings lay a foundation for characterizing the mechanisms of regulated motility in a predator of a human pathogen and a model for the ancestor of animals.

biochemistry↗

bioRxiv2019

Combining SIMS and mechanistic modelling to reveal nutrient kinetics in an algal-bacterial mutualism

Microbial communities are of considerable significance for biogeochemical processes, for the health of both animals and plants, and for biotechnological purposes. A key feature of the interactions between microbes is the exchange of nutrients between cells. Isotope labelling followed by analysis with secondary ion mass spectrometry (SIMS) can identify nutrient fluxes and heterogeneity of substrate utilisation on a single cell level. Here we present a novel approach that combines SIMS with a mechanistic model to reveal otherwise inaccessible nutrient kinetics. The method is applied to study the onset of a synthetic mutualistic partnership between a vitamin B12-dependent mutant of the alga Chlamydomonas reinhardtii and the B12-producing, heterotrophic bacterium Mesorhizobium loti, which is supported by algal photosynthesis. Results show that an initial pool of fixed carbon delays the onset of mutualistic cross-feeding, and the model allows quantification of this delay. Our method is widely applicable to other microbial systems, and will contribute to furthering a mechanistic understanding of microbial interactions.

microbiology↗

bioRxiv2019

Diurnal variations in the motility of algal populations

The motility of microalgae has been studied extensively, particularly in model microorganisms such as Chlamy-domonas reinhardtii. For this and other microalgal species, diurnal cycles are well-known to control the metabolism, growth and cell division. Diurnal variations, however, have been largely neglected in quantitative studies of motility. Here, we demonstrate using tracking microscopy how the motility statistics of C. reinhardtii are modulated by diurnal cycles. We discovered that the mean swimming speed is greater during the dark period of a diurnal cycle. From this measurement, using a hydrodynamic power balance, we conjecture that this is a result of the mean flagellar beat frequency being modulated by the flagellar ATP. Our measurements also quantify the diurnal variations of the orientational and gravitactic transport of C. reinhardtii. We discuss the implications of our frequency results in the context of cellular bioenergetics. Further, we explore the population-level consequences of diurnal variations of motility statistics by evaluating a prediction for how the gravitactic steady state changes with time during a diurnal cycle. SIGNIFICANCEWe report tracking microscopy measurements which demonstrate that the mean swimming speed of C. reinhardtii is significantly greater during the dark period of a diurnal cycle. Using hydrodynamic (low Reynolds number) power balance, we also inferred the mean flagellar beat frequency from the swimming speed, hypothesising that the observed variations in this frequency correlate with the diurnal regulation of flagellar ATP. Diurnal variations of the orientational and gravitactic transport of C. reinhardtii were also quantified and used in a continuum model to predict that, at the population scale, the steady state vertical distribution of C. reinhardtii is broader during the dark period. Our findings could have significant implications for microalgal biotechnologies, e.g. microalgal harvesting, and plankton migration in the ocean.

biophysics↗

bioRxiv2017

Microbial mutualism at a distance

The exchange of diffusive metabolites is known to control the spatial patterns formed by microbial populations, as revealed by recent studies in the laboratory. However, the matrices used, such as agarose pads, lack the structured geometry of many natural microbial habitats, including in the soil or on the surfaces of plants or animals. Here we address the important question of how such geometry may control diffusive exchanges and microbial interaction. We model mathematically mutualistic interactions within a minimal unit of structure: two growing reservoirs linked by a diffusive channel through which metabolites are exchanged. The model is applied to study a synthetic mutualism, experimentally parameterised on a model algal-bacterial co-culture. Analytical and numerical solutions of the model predict conditions for the successful establishment of remote mutualisms, and how this depends, often counterintutively, on diffusion geometry. We connect our findings to understanding complex behaviour in synthetic and naturally occurring microbial communities.

biophysics↗