Theses and Dissertations


Salih Kumru

Issuing Body

Mississippi State University


Karsi, Attila

Committee Member

Peterson, Daniel G.

Committee Member

Pinchuk, Lesya M.

Committee Member

Lawrence, Mark L.

Date of Degree


Original embargo terms


Document Type

Dissertation - Open Access


Veterinary Medical Science

Degree Name

Doctor of Philosophy


College of Veterinary Medicine


Department of Clinical Sciences


Aquaculture has potential to support the food supply of increasing world population. Flavobacterial diseases pose a serious problem in wild and aquacultured fish stocks throughout the world. Flavobacterium columnare, F. branchiophilum, and F. psychrophilum are well-known Flavobacterium species that cause important fish losses. Recently, new Flavobacterium species, isolated from diseased fish, have been reported, but their virulence mechanisms are not clear. Thus, the goal of this study was to understand pathogenicity of Flavobacterium species. To this goal, 86 Flavobacterium genomes were analyzed by comparative genomics. Predicted virulence genes were identified for all genomes. For each species, unique and shared virulence genes were determined. For all genomes, unique and common predicted antibiotic resistance genes were identified as well. Secreted proteins are important virulence factors. Thus, all encoded secretion and related systems were determined. By using different genomics approaches, F. columnare genomovar I (highly virulent to cold-water fish species like trout) and genomovar II (extremely virulent to warm-water fish species such as catfish and tilapia) genomes were analyzed, and transposon mutants using Tn4351 in six F. columnare genomovar II strain 94-081 were generated. The hemolysin and glycine cleavage protein mutants had 15% and 10% mortalities, respectively while wild-type strain caused 100% mortality. Potential virulence genes, unique proteins, and other genomic features of F. columnare genomovars were determined. Mutants targeting unique genes in valine-leucine-isoleucine biosynthesis pathway were constructed. The virulence of Fcol(DELTA)leuD and Fcol(DELTA)ilvD mutants exhibited reduced virulence.