Presenter #1: Cade Mirchandani

TITLE: Bacterial symbiont evolution across time and space: from real-time in vitro strain competition to ancient molecular mimicry

Description: The intracellular symbiont Wolbachia pipientis evolved after the divergence of arthropods and nematodes, but it reached high prevalence in many of these taxa through its abilities to infect new hosts and their germlines. Some strains exhibit long-term patterns of co-evolution with their hosts, while other strains are capable of switching hosts. This makes strain selection an important factor in symbiont-based biological control. However, little is known about the ecological and evolutionary interactions that occur when a promiscuous strain colonizes an infected host. Here, we study what occurs when two strains come into contact in host cells following horizontal transmission and infection. We focus on the faithful wMel strain from Drosophila melanogaster and the promiscuous wRi strain from Drosophila simulans using an in vitro cell culture system with multiple host cell types and combinatorial infection states. Mixing D. melanogaster cell lines stably infected with wMel and wRi revealed that wMel outcompetes wRi quickly and reproducibly, even from minuscule starting quantities. This is a nearly deterministic outcome, independent of the starting infection frequency. This competitive advantage was not exclusive to wMel’s native D. melanogaster cell background, as wMel also outgrew wRi in D. simulans cells. Overall, wRi is less adept at in vitro growth and survival than wMel and its in vivo state, revealing differences between the two strains in cellular and humoral regulation. These attributes may underlie the observed low rate of mixed infections in nature and the relatively rare rate of host-switching in most strains. Our in vitro experimental framework for estimating cellular growth dynamics of Wolbachia strains in different host species, and cell types provides the first strategy for parameterizing endosymbiont and host cell biology at high resolution. This toolset will be crucial to our application of these bacteria as biological control agents in novel hosts and ecosystems.

Bio:Cade is a third-year PhD candidate co-advised by the Russell and Corbett-Detig Labs, with research interests in evolutionary and population genomics. In the Russell Lab, he investigates the evolutionary dynamics and history of symbionts, while in the Corbett-Detig Lab, he focuses on developing tools for conservation genomics.

Presenter #2: Gabriel Penunuri

Description: Host-microbe systems represent evolutionary niches that produce coevolved biological interactions and are a key component of global health. However, these systems have historically been challenging to research due to their experimental intractability. Impactful advances in global health will be obtained by leveraging in silico screens to identify genes involved in mediating interspecific interactions. One signature of host-microbe interaction that can be detected in silico is symbiont mimicry of host molecules. Molecular mimicry can occur at any level from DNA sequences, to protein structures, to functional phenotypes. Here, we applied protein structure prediction and alignment tools to explore host-associated bacterial structural proteomes for examples of protein structure mimicry. By leveraging the Legionella pneumophila proteome and its many known structural mimics, we developed and validated a screen that can be applied to other host-microbe systems to uncover signals of protein mimicry. We have also developed an evolutionary rate analysis workflow for determining sequences undergoing selection to supplement our structural analysis. These mimics represent candidate proteins that mediate host interactions in microbial proteomes. We successfully applied this screen to other microbes with demonstrated effects on global health, Helicobacter pylori and Wolbachia pipientis, identifying protein mimic candidates in each proteome. We discuss the roles these candidates may play in important Wolbachia-induced phenotypes and show that Wolbachia infection can partially rescue the loss of one of these factors. These predictions will progress our understanding of these systems and lay the groundwork for future in vitro and in vivo experiments and bioengineering projects. This work demonstrates how a genome-wide screen for candidates of host-manipulation and intracellular survival offers an opportunity to identify functionally important genes in host-microbe systems.

Bio: Gabe is a fourth-year PhD candidate co-advised by the Russell and Corbett-Detig Labs where he has been exploring uses for computationally predicted protein data sets at the genomic level. His work between the Russell and Corbett-Detig Labs has investigated the proteomes of host-microbe systems and their potential interactions.

Presenter #3: Cole Shanks

TITLE: Clinical Implications of Founder Effects
 

Hosted by: Professor Nader Pourmand / BME

The event will now be held on Zoom.

Zoom link: https://ucsc.zoom.us/j/99867561536?pwd=4clSHMV32N2iSMBd3eOmkZc0OMsJDf.1

Meeting ID: 998 6756 1536
Passcode: 873991