About

Alecia Septer is an Associate Professor and Associate Chair for Academic Programs in the Department of Earth, Marine and Environmental Sciences at the University of North Carolina at Chapel Hill. She holds a PhD in Microbiology from the University of Georgia, where she was a National Defense Science and Engineering Graduate Fellow. Her research focuses on how interbacterial competition impacts community structure and function in marine ecosystems. Specifically, she aims to couple bacterial model systems with environmental culturing and field-based experiments to study how bacteria evolve and regulate deployment of competitive mechanisms. Connecting the molecular mechanisms of these behaviors to ecological roles, her work seeks to expand understanding of how social interactions among microorganisms affect community composition and influence animal and ecosystem health. Additionally, her research aims to inform the development of therapeutics to combat pathogens affecting humans and marine animals. Her efforts contribute to a broader understanding of microbial interactions within marine environments, emphasizing the importance of bacterial competition in ecological and health contexts.

Research topics

• Genetics
• Microbiology
• Biology
• Ecology
• Cell biology
• Biochemistry
• Chemistry

Selected publications

• Application of <i>hsp60</i> amplicon sequencing to characterize microbial communities associated with juvenile and adult <i>Euprymna scolopes</i> squid

  ISME Communications · 2025-01-01

  articleOpen accessSenior author

  Abstract The symbiotic relationship between Vibrio (Aliivibrio) fischeri and the Hawaiian bobtail squid, Euprymna scolopes, serves as a key model for understanding host–microbe interactions. Traditional culture-based methods have primarily isolated V. fischeri from the light organs of wild-caught squid, yet culture-independent analyses of this symbiotic microbiome remain limited. This study aims to enhance species-level resolution of bacterial communities associated with E. scolopes using hsp60 amplicon sequencing. We validated our hsp60 sequencing approach using pure cultures and mixed bacterial populations, demonstrating its ability to distinguish V. fischeri from other closely related vibrios and the possibility of using this approach for strain-level diversity with further optimization. This approach was applied to whole-animal juvenile squid exposed to either seawater or a clonal V. fischeri inoculum, as well as ventate samples and light organ cores from wild-caught adults. V. fischeri accounted for the majority of the identifiable taxa for whole-animal juvenile samples and comprised 94%–99% of amplicon sequence variants (ASVs) for adult light organ core samples, confirming that V. fischeri is the dominant, if not sole, symbiont typically associated with E. scolopes light organs. In one ventate sample, V. fischeri comprised 82% of reads, indicating the potential for non-invasive community assessments using this approach. Analysis of non-V. fischeri ASVs revealed that Bradyrhizobium spp. and other members of the Rhodobacterales order are conserved across juvenile and adult samples. These findings provide insight into the presence of additional microbial associations with the squid host tissue outside of the light organ that have not been previously detected through traditional culture methods.

  PublisherOA PDFDOI

• A mutualistic model bacterium is lethal to non-symbiotic hosts via the type VI secretion system

  mBio · 2025-04-17 · 3 citations

  articleOpen access

  ABSTRACT What makes a bacterium pathogenic? Since the early days of germ theory, researchers have categorized bacteria as pathogens or non-pathogens, those that cause harm and those that do not, but this binary view is not always accurate. Vibrio fischeri is an exclusive mutualistic symbiont found within the light organs of Hawaiian bobtail squid. This symbiotic interaction requires V. fischeri to utilize a range of behaviors and produce molecules that are often associated with pathogenicity. This juxtaposition of employing “pathogenic” behaviors for a symbiotic relationship led the field to focus on how V. fischeri establishes a beneficial association with its host. In this study, we observe that V. fischeri induces mortality in zebrafish embryos and Artemia nauplii. Non-lethal doses of V. fischeri lead to zebrafish growth delays and phenotypes indicative of disease. Our data also provide evidence that the conserved type VI secretion system on chromosome I (T6SS1) plays a role in the V. fischeri -induced mortality of zebrafish embryos and Artemia nauplii. These results support the hypothesis that the V. fischeri T6SS1 is involved in eukaryotic cell interactions. Despite its traditional view as a beneficial symbiont, we provide evidence that V. fischeri is capable of harming aquatic organisms, indicating its potential to be pathogenic toward non-symbiotic hosts. IMPORTANCE Vibrio fischeri is best known for its beneficial partnership with the Hawaiian bobtail squid, where it uses molecular tools often associated with disease-causing bacteria. Our research shows that V. fischeri can also cause harm, killing zebrafish embryos and brine shrimp larvae. We pinpoint one of V. fischeri ’s two type VI secretion systems (T6SS1) as a key factor in this pathogenicity. These findings reveal that V. fischeri is not strictly a mutualistic microbe but can act like a pathogen under certain conditions. This broadens our understanding of how V. fischeri could interact with different hosts and offers new insights into the dual roles bacteria can play in nature.

  PublisherDOI

• <i>Euprymna berryi</i> as a comparative model host for <i>Vibrio fischeri</i> light organ symbiosis

  Applied and Environmental Microbiology · 2025-07-10 · 4 citations

  articleOpen access

  ABSTRACT Functional studies of host-microbe interactions benefit from natural model systems that enable the exploration of molecular mechanisms at the host-microbe interface. Bioluminescent Vibrio fischeri colonize the light organ of the Hawaiian bobtail squid, Euprymna scolopes , and this binary model has enabled advances in understanding host-microbe communication, colonization specificity, in vivo biofilms, intraspecific competition, and quorum sensing. The hummingbird bobtail squid, Euprymna berryi, can be generationally bred and maintained in lab settings and has had multiple genes deleted by CRISPR approaches. The prospect of expanding the utility of the light organ model system by producing multigenerational host lines led us to determine the extent to which the E. berryi light organ symbiosis parallels known processes in E. scolopes . However, the nature of the E. berryi light organ, including its microbial constituency and specificity for microbial partners, has not been examined. In this report, we isolated bacteria from E. berryi animals and tank water. Assays of bacterial behaviors required in the host, as well as host responses to bacterial colonization, illustrate largely parallel phenotypes in E. berryi and E. scolopes hatchlings. This study reveals E. berryi to be a valuable comparative model to complement studies in E. scolopes . IMPORTANCE Microbiome studies have been substantially advanced by model systems that enable functional interrogation of the roles of the partners and the molecular communication between those partners. The Euprymna scolopes-Vibrio fischeri system has contributed foundational knowledge, revealing key roles for bacterial quorum sensing broadly and in animal hosts, for bacteria in stimulating animal development, for bacterial motility in accessing host sites, and for in vivo biofilm formation in development and specificity of an animal’s microbiome. Euprymna berryi is a second bobtail squid host, and one that has recently been shown to be robust to laboratory husbandry and amenable to gene knockout. This study identifies E. berryi as a strong symbiosis model host due to features that are conserved with those of E. scolopes , which will enable the extension of functional studies in bobtail squid symbioses.

  PublisherDOI

• Differential metaproteomics of bacteria grown <i>in vitro</i> and <i>in planta</i> reveals functions used during growth on maize roots

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-06-02 · 3 citations

  preprintOpen access

  Abstract Microbes are ubiquitous in the rhizosphere and play crucial roles in plant health, yet the metabolisms and physiologies of individual species in planta remain poorly understood. In this study, we examined microbial gene expression in response to the maize root environment for seven bacterial species originally isolated from maize roots. We grew each species individually, both in vitro in a minimal medium and in planta , and used differential metaproteomics to identify functions upregulated specifically when bacteria are grown on maize roots. We identified between 1,500 and 2,100 proteins from each species, with approximately 30-70% of these proteins being differentially abundant between the two conditions. While we found that transporter proteins were upregulated in all species in planta , all other differentially abundant functions varied greatly between species, suggesting niche specialization in root-associated microbes. Indeed, in vitro assays confirmed that Curtobacterium pusillum likely degrades plant hemicellulose, Enterobacter ludwigii may benefit the plant by phosphate solubilization, and Herbaspirillum robiniae colonizes maize roots more effectively when both of its Type VI Secretion Systems are functional. Together, our findings highlight both conserved and species-specific bacterial strategies for growth in the root environment and lay a foundation for future work investigating the mechanisms underlying plant-microbiota interactions.

  PublisherOA PDFDOI

• <i>Euprymna berryi</i> as a comparative model host for <i>Vibrio fischeri</i> light organ symbiosis

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-01-13

  preprintOpen access

  ABSTRACT Functional studies of host-microbe interactions benefit from natural model systems that enable exploration of molecular mechanisms at the host-microbe interface. Bioluminescent Vibrio fischeri colonize the light organ of the Hawaiian bobtail squid, Euprymna scolopes , and this binary model has enabled advances in understanding host-microbe communication, colonization specificity, in vivo biofilms, intraspecific competition, and quorum sensing. The hummingbird bobtail squid, Euprymna berryi, can be generationally bred and maintained in lab settings and has had multiple genes deleted by CRISPR approaches. The prospect of expanding the utility of the light organ model system by producing multigenerational host lines led us to determine the extent to which the E. berryi light organ symbiosis parallels known processes in E. scolopes . However, the nature of the E. berryi light organ, including its microbial constituency and specificity for microbial partners, have not been examined. In this report, we isolate bacteria from E. berryi animals and tank water. Assays of bacterial behaviors required in the host, as well as host responses to bacterial colonization, illustrate largely parallel phenotypes in E. berryi and E. scolopes hatchlings. This study reveals E. berryi to be a valuable comparative model to complement studies in E. scolopes . IMPORTANCE Microbiome studies have been substantially advanced by model systems that enable functional interrogation of the roles of the partners and the molecular communication between those partners. The Euprymna scolopes-Vibrio fischeri system has contributed foundational knowledge, revealing key roles for bacterial quorum sensing broadly and in animal hosts, for bacteria in stimulating animal development, for bacterial motility in accessing host sites, and for in vivo biofilm formation in development and specificity of an animal’s microbiome. Euprymna berryi is a second bobtail squid host, and one that has recently been shown to be robust to laboratory husbandry and amenable to gene knockout. This study identifies E. berryi as a strong symbiosis model host due to features that are conserved with those of E. scolopes , which will enable extension of functional studies in bobtail squid symbioses.

  PublisherOA PDFDOI

• H-NS is a conserved repressor of the type VI secretion system in <i>Vibrio fischeri</i>

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-01-30

  preprintOpen accessSenior authorCorresponding

  Abstract The type VI secretion system (T6SS) is a broadly distributed interbacterial weapon found in both beneficial and pathogenic bacteria and can enhance a microbe’s ability to colonize a host. Vibrio fischeri is a beneficial symbiont of fish and squid and a model organism for T6SS function, which is activated in high-viscosity conditions. Previously, we isolated an hns mutant in a transposon screen to identify regulators of the T6SS in the fish symbiont V. fischeri MJ11. The hns gene encodes the DNA-binding protein, H-NS, a conserved global regulator of gene expression that aids in adaptation to changing environments. Quantitative transcriptomes of the hns mutant and parent strains grown in liquid or hydrogel media revealed hns is required for the global transcriptional changes that occur during transition from lower to higher viscosity conditions. Furthermore, T6SS gene transcripts are more abundant in the hns mutant in both conditions, suggesting H-NS represses T6SS in the parent. Single-cell fluorescence microscopy confirmed hns mutant cells make more T6SS weapons in both liquid and hydrogel medium, where the hns mutant is more proficient at killing a competitor strain, compared to the wild-type parent. Finally, disrupting the hns gene in additional light organ isolates resulted in a similar derepression of T6SS, indicating H-NS is a conserved repressor of this interbacterial weapon. This work furthers our understanding of the role of H-NS as a global regulator during environmental shifts in a host-associated bacterial symbiont and expands the list of species where H-NS represses T6SS to include V. fischeri .

  PublisherOA PDFDOI

• A tripartite model system for Southern Ocean diatom-bacterial interactions reveals the coexistence of competing symbiotic strategies

  UNC Libraries · 2025-08-16

  articleOpen access

  Southern Ocean (SO) diatoms play an important role in global carbon flux, and their influence on carbon export is directly linked to interactions with epiphytic bacteria. Bacterial symbionts that increase diatom growth promote atmospheric carbon uptake, while bacterial degraders divert diatom biomass into the microbial loop where it can then be released as carbon dioxide through respiration. To further explore SO diatom-bacterial associations, a natural model system is needed that is representative of these diverse and important interactions. Here, we use concurrent cultivation to isolate a species of the ecologically-important SO diatom, Pseudo-nitzschia subcurvata, and its co-occurring bacteria. Although vitamin-depleted, axenic Pseudo-nitzschia grew poorly in culture, addition of a co-isolated Roseobacter promoted diatom growth, while addition of a co-isolated Flavobacterium negatively impacted diatom growth. Microscopy revealed both bacterial isolates are physically associated with diatom cells and genome sequencing identified important predicted functions including vitamin synthesis, motility, cell attachment mechanisms, and diverse antimicrobial weapons that could be used for interbacterial competition. These findings revealed the natural coexistence of competing symbiotic strategies of diatom-associated bacteria in the SO, and the utility of this tripartite system, composed of a diatom and two bacterial strains, as a co-culture model to probe ecological-relevant interactions between diatoms and the bacteria that compete for access to the phycosphere.

  PublisherDOI

• Abstract 1965 Two sides of the same coin: the pathogenic side of the symbiont Vibrio fischeri

  Journal of Biological Chemistry · 2025-05-01

  articleOpen access

  What makes a bacterium pathogenic? People have categorized bacteria as pathogens or non-pathogens, those that cause harm and those that do not, since the early days of germ theory. However, this binary view is not always accurate. Vibrio fischeri is an exclusive mutualistic symbiont found within the light organs of Hawaiian bobtail squid. This symbiotic interaction requires V. fischeri to utilize a range of behaviors and produce molecules that are often associated with pathogenicity. During symbiosis establishment, V.

  PublisherOA PDFDOI

• Complete genome sequence of <i>Sagittula stellata</i> strain E-37 reveals a plasmid-encoded type six secretion system

  Microbiology Resource Announcements · 2024-10-22

  articleOpen accessSenior author

  ABSTRACT We announce the complete genome sequence of Sagittula stellata strain E-37. The hybrid assembly of long and short reads revealed one chromosome and four plasmids. Furthermore, the genome analysis showed that the plasmid-encoded type six secretion system is linked to plasmid replication genes that may be common to Roseobacters.

  PublisherDOI

• A mutualistic model bacterium is lethal to non-symbiotic hosts via the type VI secretion system

  bioRxiv (Cold Spring Harbor Laboratory) · 2024-12-14

  preprintOpen access

  Abstract What makes a bacterium pathogenic? Since the early days of germ theory, researchers have categorized bacteria as pathogens or non-pathogens, those that cause harm and those that do not, but this binary view is not always accurate. Vibrio fischeri is an exclusive mutualistic symbiont found within the light organs of Hawaiian bobtail squid. This symbiotic interaction requires V. fischeri to utilize a range of behaviors and produce molecules that are often associated with pathogenicity. This juxtaposition of employing “pathogenic” behaviors for a symbiotic relationship led the field to focus on how V. fischeri establishes a beneficial association with its host. In this study, we observe that V. fischeri induces mortality in zebrafish embryos and Artemia nauplii. Non-lethal doses of V. fischeri leads to zebrafish growth delays and phenotypes indicative of disease. Our data also provide evidence that the conserved type VI secretion system on chromosome I (T6SS1) plays a role in the V. fischeri -induced mortality of zebrafish embryos and Artemia nauplii. These results support the hypothesis that the V. fischeri T6SS1 is involved in eukaryotic cell interactions. Despite its traditional view as a beneficial symbiont, we provide evidence that V. fischeri is capable of harming aquatic organisms, indicating its potential to be pathogenic toward non-symbiotic hosts.

  PublisherOA PDFDOI

Recent grants

• Genetic determinants of interbacterial competition during host colonization

  NIH · $2.2M · 2020–2030

Frequent coauthors

• Lauren Speare

  Oregon State University

  18 shared

• Stephanie Smith

  University of North Carolina at Chapel Hill

  13 shared

• Eric V. Stabb

  University of Illinois Chicago

  12 shared

• Anne K. Dunn

  University of Oklahoma

  10 shared

• Massimo Merighi

  Ginkgo BioWorks (United States)

  9 shared

• John S. Gunn

  The Ohio State University

  7 shared

• Aditi Bhatiya

  The Ohio State University

  5 shared

• Garrett Sharpe

  University of North Carolina at Chapel Hill

  5 shared

Education

• PhD, Microbiology

  University of Georgia

  2012

• BS, Microbiology

  The Ohio State University

  2004

Awards & honors

• National Defense Science and Engineering Graduate Fellow, Un…