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Mlynek KD, Toothman RG, Martinez EE, Qiu J, Richardson JB, Bozue JA. Mutation of wbtJ, a N-formyltransferase involved in O-antigen synthesis, results in biofilm formation, phase variation and attenuation in Francisella tularensis. MICROBIOLOGY (READING, ENGLAND) 2024; 170:001437. [PMID: 38421161 PMCID: PMC10924466 DOI: 10.1099/mic.0.001437] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2023] [Accepted: 01/29/2024] [Indexed: 03/02/2024]
Abstract
Two clinically important subspecies, Francisella tularensis subsp. tularensis (type A) and F. tularensis subsp. holarctica (type B) are responsible for most tularaemia cases, but these isolates typically form a weak biofilm under in vitro conditions. Phase variation of the F. tularensis lipopolysaccharide (LPS) has been reported in these subspecies, but the role of variation is unclear as LPS is crucial for virulence. We previously demonstrated that a subpopulation of LPS variants can constitutively form a robust biofilm in vitro, but it is unclear whether virulence was affected. In this study, we show that biofilm-forming variants of both fully virulent F. tularensis subspecies were highly attenuated in the murine tularaemia model by multiple challenge routes. Genomic sequencing was performed on these strains, which revealed that all biofilm-forming variants contained a lesion within the wbtJ gene, a formyltransferase involved in O-antigen synthesis. A ΔwbtJ deletion mutant recapitulated the biofilm, O-antigen and virulence phenotypes observed in natural variants and could be rescued through complementation with a functional wbtJ gene. Since the spontaneously derived biofilm-forming isolates in this study were a subpopulation of natural variants, reversion events to the wbtJ gene were detected that eliminated the phenotypes associated with biofilm variants and restored virulence. These results demonstrate a role for WbtJ in biofilm formation, LPS variation and virulence of F. tularensis.
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Affiliation(s)
- Kevin D. Mlynek
- Bacteriology Division, US ARMY Medical Research Institute of Infectious Diseases (USAMRIID), Frederick, MD, USA
| | - Ronald G. Toothman
- Bacteriology Division, US ARMY Medical Research Institute of Infectious Diseases (USAMRIID), Frederick, MD, USA
| | - Elsie E. Martinez
- Bacteriology Division, US ARMY Medical Research Institute of Infectious Diseases (USAMRIID), Frederick, MD, USA
| | - Ju Qiu
- Regulated Research Administration Division, USAMRIID, Frederick, MD, USA
| | | | - Joel A. Bozue
- Bacteriology Division, US ARMY Medical Research Institute of Infectious Diseases (USAMRIID), Frederick, MD, USA
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Mlynek KD, Cline CR, Biryukov SS, Toothman RG, Bachert BA, Klimko CP, Shoe JL, Hunter M, Hedrick ZM, Dankmeyer JL, Mou S, Fetterer DP, Qiu J, Lee ED, Cote CK, Jia Q, Horwitz MA, Bozue JA. The rLVS Δ capB/ iglABC vaccine provides potent protection in Fischer rats against inhalational tularemia caused by various virulent Francisella tularensis strains. Hum Vaccin Immunother 2023; 19:2277083. [PMID: 37975637 PMCID: PMC10760400 DOI: 10.1080/21645515.2023.2277083] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Accepted: 10/26/2023] [Indexed: 11/19/2023] Open
Abstract
Francisella tularensis is one of the several biothreat agents for which a licensed vaccine is needed. To ensure vaccine protection is achieved across a range of virulent F. tularensis strains, we assembled and characterized a panel of F. tularensis isolates to be utilized as challenge strains. A promising tularemia vaccine candidate is rLVS ΔcapB/iglABC (rLVS), in which the vector is the LVS strain with a deletion in the capB gene and which additionally expresses a fusion protein comprising immunodominant epitopes of proteins IglA, IglB, and IglC. Fischer rats were immunized subcutaneously 1-3 times at 3-week intervals with rLVS at various doses. The rats were exposed to a high dose of aerosolized Type A strain Schu S4 (FRAN244), a Type B strain (FRAN255), or a tick derived Type A strain (FRAN254) and monitored for survival. All rLVS vaccination regimens including a single dose of 107 CFU rLVS provided 100% protection against both Type A strains. Against the Type B strain, two doses of 107 CFU rLVS provided 100% protection, and a single dose of 107 CFU provided 87.5% protection. In contrast, all unvaccinated rats succumbed to aerosol challenge with all of the F. tularensis strains. A robust Th1-biased antibody response was induced in all vaccinated rats against all F. tularensis strains. These results demonstrate that rLVS ΔcapB/iglABC provides potent protection against inhalational challenge with either Type A or Type B F. tularensis strains and should be considered for further analysis as a future tularemia vaccine.
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Affiliation(s)
- Kevin D. Mlynek
- Bacteriology Division, US Army Medical Research Institute of Infectious Diseases, Frederick, MD, USA
| | - Curtis R. Cline
- Pathology Division, US Army Medical Research Institute of Infectious Diseases, Frederick, MD, USA
| | - Sergei S. Biryukov
- Bacteriology Division, US Army Medical Research Institute of Infectious Diseases, Frederick, MD, USA
| | - Ronald G. Toothman
- Bacteriology Division, US Army Medical Research Institute of Infectious Diseases, Frederick, MD, USA
| | - Beth A. Bachert
- Bacteriology Division, US Army Medical Research Institute of Infectious Diseases, Frederick, MD, USA
| | - Christopher P. Klimko
- Bacteriology Division, US Army Medical Research Institute of Infectious Diseases, Frederick, MD, USA
| | - Jennifer L. Shoe
- Bacteriology Division, US Army Medical Research Institute of Infectious Diseases, Frederick, MD, USA
| | - Melissa Hunter
- Bacteriology Division, US Army Medical Research Institute of Infectious Diseases, Frederick, MD, USA
| | - Zander M. Hedrick
- Bacteriology Division, US Army Medical Research Institute of Infectious Diseases, Frederick, MD, USA
| | - Jennifer L. Dankmeyer
- Bacteriology Division, US Army Medical Research Institute of Infectious Diseases, Frederick, MD, USA
| | - Sherry Mou
- Bacteriology Division, US Army Medical Research Institute of Infectious Diseases, Frederick, MD, USA
| | - David P. Fetterer
- Regulated Research Administration Division, U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID), Frederick, MD, USA
| | - Ju Qiu
- Regulated Research Administration Division, U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID), Frederick, MD, USA
| | - Eric D. Lee
- Pathology Division, US Army Medical Research Institute of Infectious Diseases, Frederick, MD, USA
| | - Christopher K. Cote
- Bacteriology Division, US Army Medical Research Institute of Infectious Diseases, Frederick, MD, USA
| | - Qingmei Jia
- Division of Infectious Diseases, Department of Medicine, University of California, Los Angeles, CA, USA
| | - Marcus A. Horwitz
- Division of Infectious Diseases, Department of Medicine, University of California, Los Angeles, CA, USA
| | - Joel A. Bozue
- Bacteriology Division, US Army Medical Research Institute of Infectious Diseases, Frederick, MD, USA
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Mlynek KD, Lopez CT, Fetterer DP, Williams JA, Bozue JA. Phase Variation of LPS and Capsule Is Responsible for Stochastic Biofilm Formation in Francisella tularensis. Front Cell Infect Microbiol 2022; 11:808550. [PMID: 35096655 PMCID: PMC8795689 DOI: 10.3389/fcimb.2021.808550] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2021] [Accepted: 12/22/2021] [Indexed: 11/24/2022] Open
Abstract
Biofilms have been established as an important lifestyle for bacteria in nature as these structured communities often enable survivability and persistence in a multitude of environments. Francisella tularensis is a facultative intracellular Gram-negative bacterium found throughout much of the northern hemisphere. However, biofilm formation remains understudied and poorly understood in F. tularensis as non-substantial biofilms are typically observed in vitro by the clinically relevant subspecies F. tularensis subsp. tularensis and F. tularensis subsp. holarctica (Type A and B, respectively). Herein, we report conditions under which robust biofilm development was observed in a stochastic, but reproducible manner in Type A and B isolates. The frequency at which biofilm was observed increased temporally and appeared switch-like as progeny from the initial biofilm quickly formed biofilm in a predictable manner regardless of time or propagation with fresh media. The Type B isolates used for this study were found to more readily switch on biofilm formation than Type A isolates. Additionally, pH was found to function as an environmental checkpoint for biofilm initiation independently of the heritable cellular switch. Multiple colony morphologies were observed in biofilm positive cultures leading to the identification of a particular subset of grey variants that constitutively produce biofilm. Further, we found that constitutive biofilm forming isolates delay the onset of a viable non-culturable state. In this study, we demonstrate that a robust biofilm can be developed by clinically relevant F. tularensis isolates, provide a mechanism for biofilm initiation and examine the potential role of biofilm formation.
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Affiliation(s)
- Kevin D. Mlynek
- Bacteriology Division, U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID), Frederick, MD, United States
| | - Christopher T. Lopez
- Bacteriology Division, U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID), Frederick, MD, United States
| | - David P. Fetterer
- Division of Biostatistics, U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID), Frederick, MD, United States
| | - Janice A. Williams
- Pathology Division, U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID), Frederick, MD, United States
| | - Joel A. Bozue
- Bacteriology Division, U.S. Army Medical Research Institute of Infectious Diseases (USAMRIID), Frederick, MD, United States
- *Correspondence: Joel A. Bozue,
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