Research

The squid-vibrio symbiosis
The symbiosis established between Euprymna scolopes and Vibrio fischeri is an exquisite example of co-evolution between a host and a beneficial microbe. Within 2-4 h after hatching from their eggs, juvenile squid are able to collect bacteria from surrounding seawater and facilitate their movement to the light organ located beneath the mantle. Using flagellar-based motility, V. fischeri chemotax through the pores into the light organ to establish an infection that persists throughout the lifetime of the host.

V. fischeri is a genetically tractable organism, which coupled with the ability to generate juvenile squid within a laboratory setting, enables researchers to investigate the general mechanisms beneficial microbes use to colonize and persist within their hosts. Because V. fischeri is ancestrally related to many pathogenic bacteria, e.g., Vibrio cholerae and Vibrio vulnificus, we believe our research will also provide insight into the common strategies that members of the Vibrionaceae employ to cause disease.

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Bacterial-Host Metabolic Interactions

Understanding the factors that impact the fitness of host-associated microbes ultimately depends on determining the mechanisms they use to acquire nutrients and energy for growth. Sulfur is an element that is necessary for bacterial growth. Many bacteria can utilize inorganic sulfate as their sole sulfur source; however, sulfate assimilation is energetically costly. Therefore, many bacteria utilize mechanisms to scavenge various organosulfur compounds from the environment. The Miyashiro lab investigates the molecular mechanisms used by V. fischeri to satisfy its sulfur requirements for growth within the light organ, as well as the impact that the biogeography of the bacerial populations has on expression of nutrient acquisition systems.

Project members: Nathan Wasilko, Josue Ceron and Emily Baker.

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Type VI Secretion System

The type VI secretion system (T6SS) is a needle-like nanomachine that bacterial cells express to inject damaging effectors into other cells in a contact-dependent manner.  While multiple V. fischeri strains are found within adult squid, certain strains of V. fischeri harbor this molecular weapon and express it during symbiosis establishment.  This provides T6SS+ strains with the ability to exclude or eliminate other strains from the spatially defined crypt spaces of the light organ.  The Miyashiro lab investigates the consequences that T6SS-mediated interactions have on the beneficial bacterial populations associated with the squid host, as well as the molecular regulatory mechanisms that control T6SS expression.

Project members: Kirsten Guckes, Andrew Cecere, Anjali McNeil, Peyton Moore, Britney Peachey.

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Quorum Sensing Regulation of Bioluminescence

Quorum sensing is a process in which bacteria coordinate behaviors through the synthesis and detection of small molecules called autoinducers.  In V. fischeri, quorum sensing promotes bioluminescence production in the squid light organ. The Miyashiro lab uses the squid-vibrio symbiosis as a platform to study quorum sensing within a host.  Specifically, we are interested in understanding how quorum sensing impacts the ability of V. fischeri to establish symbiosis and the extent to which populations of bacteria produce and respond to autoinducers in vivo.

Project Members: Taylor Yount and Molly Ehrig

Quorum sensing
Quorum sensing describes the process by which bacterial populations and consortia can coordinate group-level behaviors using small signaling molecules called autoinducers. In V. fischeri, quorum sensing controls bioluminescence, motility, and host-colonization factors. Our lab focuses on the small regulatory RNA Qrr1, which post-transcriptionally controls the expression of a master regulator (LitR), in response to various signals associated with quorum sensing. Current projects are focused on using genetic screens to identify novel regulators of qrr1 and examine their impact on quorum sensing within the squid light organ.

NagC regulation
NagC is a transcriptional repressor that prevents in the absence of N-acetyl-glucosamine (GlcNAc) the expression of metabolic genes involved in GlcNAc utilization. We have found that a V. fischeri mutant containing a mutation in nagC is severely compromised in its ability to initially colonize juvenile squid, although once inside the squid light organ, this mutant establishes a symbiosis indistinguishable from wild-type cells. Current projects are focused on elucidating the mechanism underlying this defect by examining the regulon of NagC in V. fischeri.