# Biotype-specific evolution

> **NIH NIH R21** · WAYNE STATE UNIVERSITY · 2024 · $188,180

## Abstract

PROJECT SUMMARY
Cholera is presently caused by O1 serogroup, El Tor biotype V. cholerae, which emerged in 1961 to initiate the
ongoing seventh pandemic. The prior 6 cholera pandemics were caused by O1 serogroup classical biotype V.
cholerae. Over the past 60 years, classical biotype has essentially disappeared from the aquatic environment
and as a cause of cholera. However, the reasons for this are unknown. V. cholerae in the environment is found
in association with numerous vertebrate fish species. The proposed work will use a zebrafish model for V.
cholerae that can investigate interactions between V. cholerae and natural aquatic hosts covering the entire
infectious cycle. Previous work found dramatic differences in the timeline of zebrafish colonization by classical
and El Tor biotypes, with classical being cleared within 72 h and El Tor able to colonize for up to 14 days with
high levels of bacterial replication. We hypothesize that this prolonged fish colonization and replication provided
a strong selective advantage to El Tor, allowing it to replace classical in environmental niches. V. cholerae El
Tor biotype has 2 pathogenicity islands termed VSP-1 and VSP-2 that classical lacks. Data from preliminary
experiments indicate an El Tor strain deleted for VSP-1 has a normal fish colonization phenotype, whereas a
strain deleted for VSP-2 is defective in prolonged colonization. Therefore, it is likely that gene(s) within VSP-2
are essential for prolonged colonization. Aim 1 of this proposal will use a progressive deletion strategy to identify
and characterize gene(s) within VSP-2 that are important for prolonged colonization and assess whether such
genes are sufficient to prolong classical colonization. On the host side, innate and adaptive immunity provide
protection from invading pathogens. Fish have innate immune responses very similar to mammals, as well as
adaptive immune responses that develop over the first 4-6 weeks of life. We hypothesize that classical biotype
is rapidly cleared by a strictly innate response, whereas El Tor can only be cleared by an adaptive immune
response. Aim 2-1 of this proposal will test these hypotheses using larval zebrafish, which have a fully functioning
innate response but an undeveloped adaptive response. Aim 2-2 will further test the hypothesis that El Tor
clearance requires adaptive immunity by using zebrafish mutants that are defective in adaptive immunity.
Completion of the proposed work, using zebrafish as an environmental V. cholerae host model, will significantly
advance our understanding of V. cholerae evolution and selective pressures in a natural reservoir. The long term
goal of this work is to better understand the V. cholerae life cycle, how it contributes to pathogenesis in humans,
and identify new strategies to combat V. cholerae disease and transmission.
.

## Key facts

- **NIH application ID:** 10761802
- **Project number:** 5R21AI171072-02
- **Recipient organization:** WAYNE STATE UNIVERSITY
- **Principal Investigator:** JEFFREY H WITHEY
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2024
- **Award amount:** $188,180
- **Award type:** 5
- **Project period:** 2023-01-06 → 2026-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10761802

## Citation

> US National Institutes of Health, RePORTER application 10761802, Biotype-specific evolution (5R21AI171072-02). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10761802. Licensed CC0.

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