Gene essentiality, miniature inverted-repeat transposable elements and pigmentation in Porphyromonas gingivalis: Convergence at a unique glycosyltransferase.
disease is a bacterially-induced ailment which results in inflammation, destruction of
oral structural integrity, loss of teeth and systemic comorbidities. It is a
polymicrobial disease in which no single bacterial species is sufficient or necessary to
elicit disease. Yet several periodontopathic species such as Porphyromonas gingivalis
have been associated with disease ... read moreoccurrence and progression. P. gingivalis is a
Gram-negative anaerobic bacterial species with a subgingival oral cavity niche. P.
gingivalis elaborates numerous virulence factors that aid in its ability to colonize,
evade immune system clearance and cause disease. The most recognizable phenotypic
feature, which doubles as an important virulence factor, is black colony pigmentation.
Pigmentation of P. gingivalis protects against phagocytosis, UV damage and oxidative
damage, and non-pigmented mutants have been shown to be avirulent in animal infection
models. Another important virulence feature, on a molecular level as opposed to
macroscopic colony pigmentation, is lipopolysaccharide. P. gingivalis can display at
least five different lipid-A versions as well as two distinct O-antigen moieties of
lipopolysaccharide, which carry different immunomodulatory capabilities. A third
virulence feature, on a genetic and genomic level, is a diverse repertoire of mobile and
repetitive elements. Intra-strain chromosomal rearrangement and transcriptional
modulation have been demonstrated for mobile and repetitive elements in P. gingivalis,
and the potential of interstrain and interspecies genetic transfer allows for clone and
population-level adaptation. We chose to further investigate the virulence factors of P.
gingivalis by adapting and developing transposon mutagenesis using a transposon system
and coupling it with sequencing technology for P. gingivalis. After generating the
transposon mutant library we characterized the in vitro essential genes of P. gingivalis
and began investigating colony pigmentation and tetrapyrrole metabolism. Through
screening the library for colony pigmentation defects and selecting the library under
variable nutrient conditions we identified a novel miniature inverted-repeat
transposable element that has connections to pigmentation and haem metabolism as well as
a lipopolysaccharide-affecting gene that is necessary for proper colony pigmentation.
Understanding the pathways and mechanisms relating to P. gingivalis colony pigmentation,
as well as the genetic elements capable of modulating the genomic and transcriptomic
landscape, will allow for better understanding of a keystone periodontopathic species on
a basic genetic and metabolic level along with potential for targeted clinical
Thesis (Ph.D.)--Tufts University, 2015.
Submitted to the Dept. of Molecular Microbiology.
Advisor: Linden Hu.
Committee: Andrew Camilli, Michael Malamy, Carol Kumamoto, and Margaret Duncan.
Keywords: Microbiology, Genetics, and Molecular biology.read less