Abstract
Edwardsiella ictaluri is a Gram-negative facultative anaerobic rod and the causative agent of enteric septicemia of channel catfish (ESC), which is one of the most prevalent diseases of catfish, causing significant economic losses in the catfish industry. E. ictaluri is resistant to complement system and macrophage killing, which results in rapid systemic septicemia. However, mechanisms of E. ictaluri stress responses under conditions of host environment are not studied well. Therefore, in this work, we report E. ictaluri stress responses during hydrogen peroxide, low pH, and catfish serum stresses as well as during catfish invasion. E. ictaluri stress responses were characterized by identifying expression of 13 universal stress protein (USP) genes (usp01-usp13) and seven USP-interacting protein genes (groEL, groES, dnaK, grpE, and clpB, grpE, relA). Data indicated that three usp genes (usp05, usp07, and usp13) were highly expressed in all stress conditions. Similarly, E. ictaluri heat shock proteins groEL, groES, dnaK, grpE, and clpB were highly expressed in oxidative stress. Also, E. ictaluri grpE and relA were highly expressed in catfish spleen and head kidney. These findings contribute to our understanding of stress response mechanisms in E. ictaluri stress response, and stress-related proteins that are essential for E. ictaluri could be potential targets for live attenuated vaccine development against ESC.
Highlights
E. ictaluri is a Gram-negative bacterium causing enteric septicemia of channel catfish (ESC), one of the most important diseases of farm-raised channel catfish in the US [1, 2]
It was shown that E. ictaluri lipopolysaccharide oligo-polysaccharide (LPS O-PS) plays a major role during catfish infection [14], and E. ictaluri tricarboxylic acid (TCA) cycle and ferric hydroxamate uptake systems contribute to E. ictaluri virulence in catfish [15,16,17,18]
We identified 13 universal stress protein (USP) and seven stress-related proteins encoded in the E. ictaluri genome [34] (Fig 1A)
Summary
E. ictaluri is a Gram-negative bacterium causing enteric septicemia of channel catfish (ESC), one of the most important diseases of farm-raised channel catfish in the US [1, 2]. E. ictaluri is a facultative intracellular pathogen capable of surviving inside catfish macrophages [3], which contributes rapid spread of the pathogen [4]. E. ictaluri virulence factors include flagella [5], extracellular capsular polysaccharide [6], lipopolysaccharide [7,8,9,10,11] outer membrane proteins [11,12,13,14,15], hemolysins [12] and chondroitinase [13]. It was shown that E. ictaluri lipopolysaccharide oligo-polysaccharide (LPS O-PS) plays a major role during catfish infection [14], and E. ictaluri tricarboxylic acid (TCA) cycle and ferric hydroxamate uptake systems contribute to E. ictaluri virulence in catfish [15,16,17,18].
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