Difference in genes between a high virulence strain G4 and a low virulence strain G18 of Flavobacterium columnare by using suppression subtractive hybridization

Flavobacterium columnare is the causative agent of columnaris disease. Different genetic groups of F. columnare show to some extent different degrees of virulence. To identify genetic differences between the high virulence strain G₄ and the low virulence strain G₁₈ of F. columnare, suppression subtractive hybridization was used. A total of 46 genes were identified from the virulent strain G₄, 35 of which showed some degree of homology with known proteins and can be classified into 11 categories: DNA replication or recombination proteins, inorganic ion transport proteins, outer membrane proteins, enterotoxin, binding proteins, YD repeat proteins, transposase, chaperon, signal transduction‐related proteins, regulatory proteins, metabolism‐related proteins. Several putative virulence factors identified in other bacteria could also be identified in the virulent strain G₄, such as ferrous iron transport protein, TonB‐dependent receptor, transposases, as well as ABC transporter permease protein. The flanking region of a putative transposase ISFclI was analysed, and a putative Rhs element was located at the downstream of the putative transposase. The analysis of isfclI gene in 24 strains of F. columnare isolated in China revealed that 11 strains have isfclI, and all the strains from Zhaoqing, Anhui and Qingjiang have isfclI.