Functional Investigation of the Type IX Secretion System Regulatory Pathway Components in Flavobacterium johnsoniae

The Type IX Secretion System (T9SS) is a protein secretion system unique to the phylum Bacteroidetes. The T9SS is a large complex composed of several different functional proteins that extend through the inner and outer membranes of the cell. This T9SS is responsible for secretion of high molecular weight organic polymer digesting enzymes, motility adhesins, and virulence factors in members of the Bacteroidetes. The T9SS gene expression is known to be regulated by a two-component system (PorX and PorY) and a sigma factor protein (SigP) in the human oral pathogen Porphyromonas gingivalis, a non-motile member of the phylum Bacteroidetes that causes gum diseases. Mutants lacking these regulatory components are deficient in secretion of protease virulence factors in P. gingivalis. In this research, we aim to investigate the functions of the PorX/PorY two component system and SigP in Flavobacterium johnsoniae, a model organism for Bacteroidetes gliding motility and the T9SS studies. F. johnsoniae uses the T9SS to secrete adhesins along its outer membrane, allowing for gliding motility across solid surfaces. This organism also produces chitinase (ChiA) and proteases, enzymes that are required for digestion of chitin and proteins, respectively. We have created mutants lacking porX, porY and sigP in F. johnsoniae. Preliminary results show that the porX, porY, and sigP deletion mutants are deficient in chitinase and protease activities, suggesting that they may be involved in down-regulation of the T9SS gene expression. This functional investigation provides more information about gene regulation of a relatively novel secretion system, as well investigating possibilities for drug therapies in pathogenic species of Bacteroidetes