- The long-term goals of the proposed research program are to provide insight into the complex dialogue that occurs each generation between humans and their microbiota during the critical period following birth. Recent research has indicated a strong correlation between outcomes of these early events and life-long health. However, the inaccessibility of colonized tissues and high diversity of the microbiota renders an in-depth study of early colonization of human tissues extremely challenging. When faced with such complex phenomena, biologists often turn to simpler model systems to provide insights into evolutionarily conserved features and reveal basic principles. To decipher the cellular and molecular mechanisms underlying the initiation of bacterial associations with apical surfaces of mucosal epithelia, the proposed program exploits the binary symbiosis between the bacterium Vibrio fischeri and its squid host, Euprymna scolopes. This relatively simple association has been studied for over two decades as a model for the chronic colonization of mucosa by Gram-negative bacteria. As in humans, the squid-vibrio association begins anew each generation, requiring a `winnowing' of other environmental bacteria that results in persistent association restricted to the coevolved partners. In this system, the process of symbiosis initiation occurs across ~100 microns over minutes to hours. It can be directly imaged in its entirety using confocal microscopy, which offers the rare opportunity to define, with high temporal and spatial resolution, the reciprocal molecular and biochemical dialogue that results in the establishment of a specific, life-long beneficial symbiosis. This project brings together two collaborators, each with expertise in the biology of one of the symbiotic partners, and introduces new technology to the study of host-microbe interactions, including: Nanoscale Secondary Ion Mass Spectrometry (NanoSIMS), which allows precision tracking of symbiont molecules into host tissues; Hybridization-Chain-Reaction Fluorescent In Situ Hybridization (HCR-FISH), which enables visualization of rare transcripts in host and symbiont cells; NanoString, a new technology for simultaneous analysis of dozens to hundreds of targeted transcripts; and high-efficiency RNAseq, which produces robust transcriptional libraries from as little as 10 ng total RNA (~105 bacteria).
Specific aims to be addressed are: (1) the examination of how symbiotic bacterial strain variation affects symbiosis onset and persistence; (2) the characterization of outer membrane vesicle (OMV) contents, their trafficking into host cells, and host responses to OMV cargo; and, (3) the investigation of the roles of vibrio virulence determinants in a non-pathogenic association. An understanding of the human microbiome is in its infancy, and this frontier field is currently at the stage of building paradigms. Within this context, as the squid-vibrio system has in the past, the results of the current study will shed light upon fundamental principles governing the onset of both beneficial and pathogenic associations.

Public Health Relevance

A critical period in the colonization of humans and other animals by both the normal microbiota and encroaching microbial pathogens is the very first minutes to hours of their encounter with host tissues. The interplay between the two partners during this period determines whether a healthy association will be fostered, a dysfunctional microbial community will develop, or a frank pathogenesis will ensue. A collaborative team of scientists, using host cell biology, innovative imaging, microbial genetics, and genomics/transcriptomics approaches, will discover the molecular and biochemical mechanisms underlying this crucial period, defining the general principles that govern the reciprocal interactions between host cells and the microbes in their environment.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Method to Extend Research in Time (MERIT) Award (R37)
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Bacterial Pathogenesis Study Section (BACP)
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Baqar, Shahida
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University of Hawaii
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United States
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Kremer, Natacha; Koch, Eric J; El Filali, Adil et al. (2018) Persistent Interactions with Bacterial Symbionts Direct Mature-Host Cell Morphology and Gene Expression in the Squid-Vibrio Symbiosis. mSystems 3:
Koehler, Sabrina; Gaedeke, Roxane; Thompson, Cecilia et al. (2018) The model squid-vibrio symbiosis provides a window into the impact of strain- and species-level differences during the initial stages of symbiont engagement. Environ Microbiol :
Peyer, Suzanne M; Kremer, Natacha; McFall-Ngai, Margaret J (2018) Involvement of a host Cathepsin L in symbiont-induced cell death. Microbiologyopen 7:e00632
Bongrand, Clotilde; Ruby, Edward G (2018) Achieving a multi-strain symbiosis: strain behavior and infection dynamics. ISME J :
Nawroth, Janna C; Guo, Hanliang; Koch, Eric et al. (2017) Motile cilia create fluid-mechanical microhabitats for the active recruitment of the host microbiome. Proc Natl Acad Sci U S A 114:9510-9516
Aschtgen, Marie-Stephanie; Wetzel, Keith; Goldman, William et al. (2016) Vibrio fischeri-derived outer membrane vesicles trigger host development. Cell Microbiol 18:488-99
Schwartzman, Julia A; Ruby, Edward G (2016) Stress as a Normal Cue in the Symbiotic Environment. Trends Microbiol 24:414-424
Nikolakakis, K; Monfils, K; Moriano-Gutierrez, S et al. (2016) Characterization of the Vibrio fischeri Fatty Acid Chemoreceptors, VfcB and VfcB2. Appl Environ Microbiol 82:696-704
Schwartzman, Julia A; Ruby, Edward G (2016) A conserved chemical dialog of mutualism: lessons from squid and vibrio. Microbes Infect 18:1-10
Schwartzman, Julia A; Koch, Eric; Heath-Heckman, Elizabeth A C et al. (2015) The chemistry of negotiation: rhythmic, glycan-driven acidification in a symbiotic conversation. Proc Natl Acad Sci U S A 112:566-71

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