Utilization of transferrin and salmon serum as sources of iron by typical and atypical strains of Aeromonas salmonicida

Abstract

The ability of typical and atypical strains of Aemmnas salmonicida to utilize non-haem sources of protein-bound iron was evaluated. (i) In a plate bioassay, the suppression of growth imposed on typical and atypical A. Ealmonicida by addition of the high-aff inity iron chelator ethylenediamine-di(ohydroxyphenylacetic acid) (EDDA) to the growth medium was reversed by the addition of 30% or 90% iron-saturated bovine or human transferrin (Tf) or lactoferrin (Lf) to the growth medium. (ii) The mechanism of obtaining iron from Tf was investigated by the addition of bovine Tf contained within a dialysis bag. The reversal of iron-restricted growth suppression differed between the strains in that the atypical strains were unable to utilize Tf contained within a dialysis bag while the typical strains were able to do so.This suggested a siderophore-mediated uptake of iron from Tf by the typical strains, which are known to produce siderophores while atypical strains do not. (iii) A solid-phase binding assay using horseradish-peroxidase-conjugated or biotinylated Tf or Lf failed to detect Tf/Lf-binding activity using whole typical or atypical cells. (iv) When atypical extracellular products (ECP) plus bovine Tf or salmon serum were enclosed in a dialysis bag, diffusible products were released which could reverse the EDDA-imposed growth suppression of an atypical strain. This reversal was negated by inhibition of the ECP metalloprotease with EDTA. (v) Purified 70 kDa serine protease of a typical strain was able to digest bovine Tf to low molecular mass fragments as observed in SDS-PAGE. These results indicate that typical and atypical strains of A. sslmonicida differ in their mechanism of utilization of non-haem proteinbound sources of iron. Typical strains utilize T f via a siderophore-mediated mechanism and are also able to digest Tf with the extracellular serine protease. Atypical strains utilize Tf by a siderophore-independent mechanism probably involving the proteolytic degradation of Tf by the extracellular metal loprotease.

Occurrence and significance of atypical Aeromonas salmonicida in non-salmonid and salmonid fish species:a review

“…Such mechanisms include the production of siderophores and the induction of transferrin-binding proteins under conditions of iron restriction. Siderophore production has not been observed in atypical strains (Chart & Trust 1983, Hirst et al 1991, and iron-uptake has been suggested to be performed by a probable proteolytic degradation of transferrin bound iron by an extracellular metalloprotease (Hirst & Ellis 1996). A probable correlation between established protease groups (Gudmundsdottir 1996) and uptake of iron might explain the large variations in virulence observed in different atypical strains (Table 6).…”

Temperature dependent activation of leucocyte populations of rainbow trout, Oncorhynchus mykiss, after intraperitoneal immunisation with Aeromonas salmonicida

“…A polysaccharide capsule preventing phagocytosis by activated macrophages in late infection was formed in vivo and under glucose enriched conditions in vitro [10,11]. The extracellular toxins lyse host cells, including leucocytes and erythrocytes, enhancing the availability of amino acids and iron for bacterial growth in vivo [5,9,[12][13][14][15]. Furthermore, growth of the bacterium in vivo led to expression of novel antigens increasing the resistance to the oxidative killing mechanisms of the host [10,16].…”

Monoclonal antibodies against AsaP1, a major exotoxin of the fish pathogen Aeromonas salmonicida subsp. achromogenes, and their application in ELISA

“…1990 ). Recent results described by Hirst & Ellis (1996) suggest that this exoenzyme may be implicated in the siderophore‐independent iron acquisition of this bacterial pathogen. In vitro, AsaP1 was not cytotoxic but possessed immunomodulatory features ( Gudmundsdóttir et al .…”