# Investigating Rickettsia Interspecies and Host-Specific Lipopolysaccharide Variation

> **NIH NIH R21** · UNIVERSITY OF MARYLAND BALTIMORE · 2022 · $231,750

## Abstract

PROJECT SUMMARY
 Rickettsiae are Gram-negative obligate intracellular Alphaproteobacteria and metabolic parasites with a wide range
of eukaryotic hosts. Across the Rickettsia tree, vector-borne pathogens (i.e., Spotted Fever Group (SFG) and Typhus
Group (TG) disease agents) are interspersed with many endosymbionts and other species of unknown pathogenicity.
A treasure trove of sequenced genomes allows for robust comparisons to illuminate mechanisms behind vector
transmission and pathogenesis. This is crucial for human health, as rising deforestation and urbanization are fueling
spikes in rickettsial diseases across the US, with the ever-present chance tetracycline-resistant strains will emerge.
 Dr. Gillespie uses phylogenomics to identify lineage specific factors that are subsequently characterized for roles
in rickettsial pathogenesis. Teaming with Dr. Ernst, an expert on bacterial LPS, has resulted in the very recent
discovery that not all Rickettsia lipid A is created equal! Lipid A, the membrane component of LPS that is among
the most proinflammatory molecules known, diverges in acyl chain length at a definable point in SFG Rickettsiae
evolution − one of the deadliest pathogens (the Rocky Mountain Spotted Fever agent R. rickettsi) adopts a 2’ acyl
chain like that found in the highly potent E. coli lipid A! This implies Rickettsiae lipid A interacts variably with the host
MD-2/TLR4 receptor. We have also made two other discoveries indicating LPS is variable across Rickettsia
species. First, the polysaccharide synthesis operon (pso), which encodes enzymes involved in synthesis of LPS
carbohydrate moiety (CaMo), is highly divergent across Rickettsia genomes. Second, genes encoding two enzymes
that potential modify LPS with phosphoethanolamine (pEtN by Ept) and phosphorylcholine (ChoP by LicD) have been
acquired by lateral gene transfer and are pseudogenized in some non-pathogens that don’t infect vertebrates!
 These collective data strengthen our hypothesis that LPS is variable across diverse Rickettsiae; further, given the
physiological and immunological differences between arthropod and vertebrate cells, we posit that Rickettsia LPS
structure changes during shifts between arthropod and vertebrate host environments, similar to other bacteria (i.e.
Yersinia pestis and Francisella tularensis), and may be a mechanism for silencing the host innate immune system.
 In this proposal, two independent (yet complementary) Specific Aims are designed to test these hypotheses. First
(AIM 1), we will use FLATn, a rapid method to yield lipid A structures with minimal input sample and no chemical
extraction, to determine lipid A acyl chain length variability for ten diverse rickettsiae infecting both arthropod and
vertebrate cells. Next (AIM 2), a subset of these species will be used to characterize CaMo structures and gauge
gene expression of ps, ept, and licD; furthermore, we will characterize Rickettsia typhi pEtN addition to LPS and mine
Rickettsia genome...

## Key facts

- **NIH application ID:** 10527408
- **Project number:** 1R21AI166832-01A1
- **Recipient organization:** UNIVERSITY OF MARYLAND BALTIMORE
- **Principal Investigator:** Joseph J Gillespie
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $231,750
- **Award type:** 1
- **Project period:** 2022-06-01 → 2024-05-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10527408

## Citation

> US National Institutes of Health, RePORTER application 10527408, Investigating Rickettsia Interspecies and Host-Specific Lipopolysaccharide Variation (1R21AI166832-01A1). Retrieved via AI Analytics 2026-05-25 from https://api.ai-analytics.org/grant/nih/10527408. Licensed CC0.

---

*[NIH grants dataset](/datasets/nih-grants) · CC0 1.0*