Hayley McCausland

Bio: Hayley McCausland is an academic researcher from University of California, Berkeley. The author has contributed to research in topics: Magnetosome & Entomophthora muscae. The author has an hindex of 4, co-authored 6 publications receiving 77 citations.

Magnetic genes: Studying the genetics of biomineralization in magnetotactic bacteria.

Abstract: Many species of bacteria can manufacture materials on a finer scale than those that are synthetically made. These products are often produced within intracellular compartments that bear many hallmarks of eukaryotic organelles. One unique and elegant group of organisms is at the forefront of studies into the mechanisms of organelle formation and biomineralization. Magnetotactic bacteria (MTB) produce organelles called magnetosomes that contain nanocrystals of magnetic material, and understanding the molecular mechanisms behind magnetosome formation and biomineralization is a rich area of study. In this Review, we focus on the genetics behind the formation of magnetosomes and biomineralization. We cover the history of genetic discoveries in MTB and key insights that have been found in recent years and provide a perspective on the future of genetic studies in MTB.

Robust manipulation of the behavior of Drosophila melanogaster by a fungal pathogen in the laboratory

Abstract: We are surrounded by billions of microbes, many of which live on or even inside us. With some of these tiny creatures we share a mutually beneficial relationship, and they help to protect and nourish us in return for food and shelter. But some microbes have taken this relationship a step further and evolved the ability to manipulate the behavior of their host animals to their advantage. For example, certain fungi can hijack the nervous systems of ants, turning them into ‘zombies’ that are forced to climb to the precise height of a plant with the right conditions for the fungus to grow. Another fungus, called Entomophthora muscae, induces a similar behavior in flies. Like with the ants, this fungus forces the flies to climb to a high location and to attach themselves to the plant with their mouthparts, so providing a basis for the fungus to grow. Due to the lack of knowledge and tools that allow us to study the genes and cells of many of these host species, it remains unclear how these microbes can manipulate other animals and change their behavior. Now, Elya et al. wanted to find out whether this process can be examined in a well-known ‘model organism’, the fruit fly. The fruit flies were infected with E. muscae obtained from the wild and activity patterns in the genes of both organisms were tracked. One day after infection with the fungus, the flies developed a strong immune response to the invader, and many genes involved in the immune system were overactive. After two days, the fungus started to adopt the shape that eventually kills the flies and began to invade the nervous system. By the third day, the fungus had spread throughout the body and most flies died around four to five days following infection. Two to three hours after the flies had died, the digestive and reproductive systems had been consumed by the fungus and the nervous system was in the process of being degraded. Contrary to other infected organisms, the fungus got inside the fly’s nervous system during the early stages of infection. This could be an important clue as to how the fungus changes the fly’s behavior, but more research is needed to confirm this. The techniques developed in the study of Elya et al. can now be used to study how exactly microbes affect their hosts. A better knowledge of the relationship between these organisms will provide new insight into how animal behaviors are encoded and generated.

Nano and Microtechnologies for the Study of Magnetotactic Bacteria

Abstract: Author(s): Tay, A; McCausland, H; Komeili, A; Di Carlo, D | Abstract: Magnetotactic bacteria (MTB) naturally synthesize magnetic nanoparticles that are wrapped in lipid membranes. These membrane-bound particles, which are known as magnetosomes, are characterized by their narrow size distribution, high colloidal stability, and homogenous magnetic properties. These characteristics of magnetosomes confer them with significant value as materials for biomedical and industrial applications. MTB are also a model system to study key biological questions relating to formation of bacterial organelles, metal homeostasis, biomineralization, and magnetoaerotaxis. The similar size scale of nano and microfluidic systems to MTB and ease of coupling to local magnetic fields make them especially useful to study and analyze MTB. In this Review, a summary of nano- and microtechnologies that are developed for purposes such as MTB sorting, genetic engineering, and motility assays is provided. The use of existing platforms that can be adapted for large-scale MTB processing including microfluidic bioreactors is also described. As this is a relatively new field, future synergistic research directions coupling MTB, and nano- and microfluidics are also suggested. It is hoped that this Review could start to bridge scientific communities and jump-start new ideas in MTB research that can be made possible with nano- and microfluidic technologies.

A fungal pathogen that robustly manipulates the behavior of Drosophila melanogaster in the laboratory

Abstract: Many microbes induce striking behavioral changes in their animal hosts, but how they achieve these effects is poorly understood, especially at the molecular level. This is due in large part to the lack of a robust system amenable to modern molecular manipulation. We recently discovered a strain of the behavior-manipulating fungal fly pathogen Entomophthora muscae infecting wild adult Drosophila in Northern California, and developed methods to reliably propagate the infection in lab.-reared Drosophila melanogaster. Our lab.-infected flies manifest the moribund behaviors characteristic of E. muscae infections: on their final day of life they climb to a high location, extend their proboscides and become affixed to the substrate, then finally raise their wings to strike a characteristic death pose that clears a path for spores that are forcibly ejected from their abdomen to land on and infect other flies. Using a combination of descriptive, histological, molecular and genomic techniques, we have carefully characterized the progress of infection in lab.-reared flies in both the fungus and host. Enticingly, we reveal that E. muscae invades the fly nervous system early in infection, suggesting a direct means by which the fungus could induce behavioral changes. Given the vast toolkit of molecular and neurobiological tools available for D. melanogaster, we believe this newly established E. muscae system will permit rapid progress in understanding how microbes manipulate animal behavior.

Mapping the genetic landscape of biomineralization in Magnetospirillum magneticum AMB-1 with RB-Tnseq

Abstract: Magnetotactic bacteria (MTB) are a phylogenetically diverse group of bacteria remarkable for their ability to biomineralize magnetite (Fe3O4) or greigite (Fe3S4) in organelles called magnetosomes. The majority of genes required for magnetosome formation are encoded by a magnetosome gene island (MAI). Most previous genetic studies in MTB have focused on the MAI, using screens to identify key MAI genes or targeted genetics to isolate specific genes and their function in one specific growth condition. Here, we conducted random barcoded transposon mutagenesis (RB-TnSeq) in Magnetospirillum magneticum AMB-1 to identify the global genetic requirements for magnetosome formation under different growth conditions. We generated a library of 184,710 unique strains in a wild-type background, generating ~34 mutant strains for each gene. RB-TnSeq also allowed us to determine the essential gene set of AMB-1 under standard laboratory growth conditions. To pinpoint novel genes that are important for magnetosome formation, we subjected the library to magnetic selection screens in varied growth conditions. We compared biomineralization in standard growth conditions to biomineralization in high iron and anaerobic conditions, respectively. Strains with transposon insertions in the MAI gene mamT had an exacerbated biomineralization defect under both high iron and anerobic conditions compared to standard conditions, adding to our knowledge of the role of MamT in magnetosome formation. Mutants in amb4151, a gene outside of the MAI, are more magnetic than wild-type cells under anaerobic conditions. All three of these phenotypes were validated by creating a markerless deletion strain of the gene and evaluating with TEM imaging. Overall, our results indicate that growth conditions affect which genes are required for biomineralization and that some MAI genes may have more nuanced functions than was previously understood.

Genomic Analysis of European Drosophila melanogaster Populations Reveals Longitudinal Structure, Continent-Wide Selection, and Previously Unknown DNA Viruses

Abstract: Genetic variation is the fuel of evolution, with standing genetic variation especially important for short-term evolution and local adaptation. To date, studies of spatiotemporal patterns of genetic variation in natural populations have been challenging, as comprehensive sampling is logistically difficult, and sequencing of entire populations costly. Here, we address these issues using a collaborative approach, sequencing 48 pooled population samples from 32 locations, and perform the first continent-wide genomic analysis of genetic variation in European Drosophila melanogaster. Our analyses uncover longitudinal population structure, provide evidence for continent-wide selective sweeps, identify candidate genes for local climate adaptation, and document clines in chromosomal inversion and transposable element frequencies. We also characterize variation among populations in the composition of the fly microbiome, and identify five new DNA viruses in our samples.

Magnetic genes: Studying the genetics of biomineralization in magnetotactic bacteria.

Abstract: Many species of bacteria can manufacture materials on a finer scale than those that are synthetically made. These products are often produced within intracellular compartments that bear many hallmarks of eukaryotic organelles. One unique and elegant group of organisms is at the forefront of studies into the mechanisms of organelle formation and biomineralization. Magnetotactic bacteria (MTB) produce organelles called magnetosomes that contain nanocrystals of magnetic material, and understanding the molecular mechanisms behind magnetosome formation and biomineralization is a rich area of study. In this Review, we focus on the genetics behind the formation of magnetosomes and biomineralization. We cover the history of genetic discoveries in MTB and key insights that have been found in recent years and provide a perspective on the future of genetic studies in MTB.

Methods for the study of innate immunity in Drosophila melanogaster.

Abstract: From flies to humans, many components of the innate immune system have been conserved during metazoan evolution. This foundational observation has allowed us to develop Drosophila melanogaster, the fruit fly, into a powerful model to study innate immunity in animals. Thanks to an ever-growing arsenal of genetic tools, an easily manipulated genome, and its winning disposition, Drosophila is now employed to study not only basic molecular mechanisms of pathogen recognition and immune signaling, but also the nature of physiological responses activated in the host by microbial challenge and how dysregulation of these processes contributes to disease. Here, we present a collection of methods and protocols to challenge the fly with an assortment of microbes, both systemically and orally, and assess its humoral, cellular, and epithelial response to infection. Our review covers techniques for measuring the reaction to microbial infection both qualitatively and quantitatively. Specifically, we describe survival, bacterial load, BLUD (a measure of disease tolerance), phagocytosis, melanization, clotting, and ROS production assays, as well as efficient protocols to collect hemolymph and measure immune gene expression. We also offer an updated catalog of online resources and a collection of popular reporter lines and mutants to facilitate research efforts. This article is categorized under: Technologies > Analysis of Cell, Tissue, and Animal Phenotypes.

Microfluidic Screening of Electric Fields for Electroporation

Abstract: Electroporation is commonly used to deliver molecules such as drugs, proteins, and/or DNA into cells, but the mechanism remains poorly understood. In this work a rapid microfluidic assay was developed to determine the critical electric field threshold required for inducing bacterial electroporation. The microfluidic device was designed to have a bilaterally converging channel to amplify the electric field to magnitudes sufficient to induce electroporation. The bacterial cells are introduced into the channel in the presence of SYTOX(®), which fluorescently labels cells with compromised membranes. Upon delivery of an electric pulse, the cells fluoresce due to transmembrane influx of SYTOX(®) after disruption of the cell membranes. We calculate the critical electric field by capturing the location within the channel of the increase in fluorescence intensity after electroporation. Bacterial strains with industrial and therapeutic relevance such as Escherichia coli BL21 (3.65 ± 0.09 kV/cm), Corynebacterium glutamicum (5.20 ± 0.20 kV/cm), and Mycobacterium smegmatis (5.56 ± 0.08 kV/cm) have been successfully characterized. Determining the critical electric field for electroporation facilitates the development of electroporation protocols that minimize Joule heating and maximize cell viability. This assay will ultimately enable the genetic transformation of bacteria and archaea considered intractable and difficult-to-transfect, while facilitating fundamental genetic studies on numerous diverse microbes.