Chemotactic factors of Flavobacterium columnare to skin mucus of healthy channel catfish (Ictalurus punctatus).

To gain an insight into the chemotactic factors involved in chemotaxis, we exposed a virulent strain of Flavobacterium columnare to various treatments, followed by analysis of its chemotactic activity. The chemotactic activity of F. columnare was significantly (P<0.05) inhibited when cells were pretreated by sodium metaperiodate, and a major portion of the capsular layer surrounding the cells was removed. Pretreatment of F. columnare with D-mannose, D-glucose and N-acteyl-D-glucosamine significantly (P<0.05) inhibited its chemotaxis activity, whereas pretreatment of cells with d-fructose, L-fucose, D-glucosamine, d-galactosamine, D-sucrose and N-acetyl-D-galactosamine failed to inhibit its chemotactic activity. These results indicate that at least three carbohydrate-binding receptors (D-mannose, D-glucose and N-acteyl-D-glucosamine) associated with the capsule of F. columnare might be involved in the chemotactic responses. The relative transcriptional levels of three gliding motility genes (gldB, gldC, gldH) of F. columnare compared with 16S rRNA gene following the exposure of F. columnare to catfish skin mucus were evaluated by quantitative PCR (qPCR). qPCR results revealed that the transcriptional level of gldH was significantly (P<0.001) upregulated in normal F. columnare at 5 min postexposure to the catfish mucus. However, when F. columnare were pretreated with D-mannose, there was no upregulation of gliding motility genes. Taken together, our results suggest that carbohydrate-binding receptors play important roles in the chemotactic response to catfish mucus.