Borrelia peptidoglycan interacting Protein (BpiP) contributes to the fitness of Borrelia burgdorferi against host-derived factors and influences virulence in mouse models of Lyme disease.

Yue Chen,Sean M Vargas,Trever C Smith,Karen L Wozniak,Janakiram Seshu,Taylor Macmackin Ingle,Sai Lakshmi Rajasekhar Karna,Floyd L Wormley,D Scott Samuels

doi:10.1371/journal.ppat.1009535

Yue Chen, Sean M Vargas + Show 7 more

Open Access

https://doi.org/10.1371/journal.ppat.1009535

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Abstract

The Peptidoglycan (PG) cell wall of the Lyme disease (LD) spirochete, Borrelia burgdorferi (Bb), contributes to structural and morphological integrity of Bb; is a persistent antigen in LD patients; and has a unique pentapeptide with L-Ornithine as the third amino acid that cross-links its glycan polymers. A borrelial homolog (BB_0167) interacted specifically with borrelilal PG via its peptidoglycan interacting motif (MHELSEKRARAIGNYL); was localized to the protoplasmic cylinder of Bb; and was designated as Borrelia peptidoglycan interacting Protein (BpiP). A bpiP mutant displayed no defect under in vitro growth conditions with similar levels of several virulence-related proteins. However, the burden of bpiP mutant in C3H/HeN mice at day 14, 28 and 62 post-infection was significantly lower compared to control strains. No viable bpiP mutant was re-isolated from any tissues at day 62 post-infection although bpiP mutant was able to colonize immunodeficient SCID at day 28 post-infection. Acquisition or transmission of bpiP mutant by Ixodes scapularis larvae or nymphs respectively, from and to mice, was significantly lower compared to control strains. Further analysis of bpiP mutant revealed increased sensitivity to vancomycin, osmotic stress, lysosomal extracts, human antimicrobial peptide cathelicidin-LL37, complement-dependent killing in the presence of day 14 post-infection mouse serum and increased internalization of CFSC-labeled bpiP mutant by macrophages and dendritic cells compared to control strains. These studies demonstrate the importance of accessory protein/s involved in sustaining integrity of PG and cell envelope during different phases of Bb infection.

Highlights

Lyme disease is the most common tick-borne infectious disease in the US with more than 40,000 confirmed and around 300,000 estimated infections occurring each year according to Centers for Disease Control and Prevention [1]
Peptidoglycan (PG) cell wall contributes to structural integrity of Borrelia burgdorferi (Bb), remodeling of its cell envelope in response to environmental signals and in modulation of antimicrobial responses in different hosts during the infectious cycle
We demonstrate the role of a borrelial protein, designated as Borrelia peptidoglycan interacting Protein (BpiP), in the patho-physiology of Bb

Summary

Introduction

Lyme disease is the most common tick-borne infectious disease in the US with more than 40,000 confirmed and around 300,000 estimated infections occurring each year according to Centers for Disease Control and Prevention [1]. Bb is constrained by 1) environmental signals; 2) limited/variable levels of key nutrients; and 3) effects of numerous antimicrobial factors impacting its survival in ticks and vertebrate hosts [2, 5]. To overcome these bottlenecks, Bb undergoes extensive remodeling of its cell envelope—comprising of an inner cytoplasmic membrane, the peptidoglycan (PG) cell wall and the outer membrane with a constellation of primarily lipoproteins—connecting its metabolism and survival strategies to availability/transport of nutrients to survive and colonize highly divergent hosts. The molecular mechanisms and key determinants that contribute to remodeling and structural integrity of the borrelial cell envelope facilitating host-specific adaptation of Bb are unclear and are open areas of investigation

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