The survival/ adaptation of Porphyromonas gingivalis to the inflammatory environment of the periodontal pocket requires an ability to overcome oxidative stress. Several functional classes of genes, depending on the severity and duration of the exposure, were induced in P. gingivalis under H2O2-induced oxidative stress, including the PG0686 gene which was upregulated ca. 10-fold. In addition, its upregulation was also observed in the presence of oxygen and nitric oxide. This study is aimed to further characterize the function of this gene in response to H2O2. PG_0686, annotated as a hypothetical protein of unknown function, is a 60 kDa protein with a diguanylate cyclase (DGC)-like fold and carries other domains including hemerythrin, a PAS10 domain, and Domain of Unknown Function (DUF)-1858. PG_0686 is missing the classical active site conserved sequence motif (GGD(/E)EF) commonly observed in the DGC of other bacteria. PG_0686-related proteins are observed in other anaerobic bacterial species. The isogenic mutant P. gingivalis FLL361 (ΔPG0686::ermF) showed increased sensitivity to H2O2 and decreased gingipain activity compared to the parent strain. Transcriptome analysis of P. gingivalis FLL361 showed the dysregulation of several gene clusters/operons, known oxidative stress resistance genes and transcriptional regulators including PG_2212, CdhR and PG_1181 that were upregulated under normal anaerobic conditions. The purified recombinant PG_0686 protein can catalyze c-di-GMP formation from GTP. The intracellular level of c-di-GMP in P. gingivalis FLL361 was significantly decreased compared to the parent strain. Collectively, our data suggest a global regulatory property for PG_0686 that may be part of an unconventional second messenger signaling system in P. gingivalis. Moreover, it may coordinately regulate a pathway(s) vital for protection against environmental stress and is significant in the pathogenicity of the P. gingivalis, and likely other anaerobes.

LLU Discipline

Microbiology and Molecular Genetics




School of Medicine

First Advisor

Nathan R. Wall

Second Advisor

Hansel M. Fletcher

Third Advisor

Mark S. Johnson

Fourth Advisor

Charles Wang

Fifth Advisor

Christopher Perry

Sixth Advisor

Chia-En A. Chang

Degree Name

Doctor of Philosophy (PhD)

Degree Level


Year Degree Awarded


Date (Title Page)






Page Count

xxxii, 256 p.

Digital Format


Digital Publisher

Loma Linda University Libraries

Usage Rights

This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.


Loma Linda University Electronic Theses and Dissertations

Collection Website



Loma Linda University. Del E. Webb Memorial Library. University Archives