Cadmium effects onIchthyophthirius: evidence for metal-sequestration in fish tissues following administration of recombinant vaccines

Abstract

We are developing Tetrahymena thermophila as a delivery system for recombinant vaccines against parasitic protozoa, including the common fish parasite, Ichthyophthirius multifiliis. T. thermophila cell lines expressing I. multifiliis genes under the control of a cadmium-inducible metallothionein gene promoter conferred strong protection against a lethal parasite challenge when administered parenterally to naive fish. Nevertheless, given that heavy metals can be toxic to parasites, a question arose as to whether protection resulted from Cd residues carried over with the vaccine, rather than acquired immunity per se. To address this issue, we examined the sensitivity of I. multifiliis to Cd in vitro and determined Cd concentrations in different host tissues following i.p. injection of juvenile channel catfish with the recombinant vaccine. We found that CdCl2 at concentrations > or = 50 ppb were lethal to I. multifiliis theronts in vitro. Furthermore, Cd concentrations were clearly elevated in fish tissues and reached levels equivalent to 74 ng/g wet weight (74 ppb) in the skin within 14 days of injection with recombinant T. thermophila. Nevertheless, fish injected with non-transformed Tetrahymena grown in the presence or absence of CdCl2 showed no significant difference in either relative survival or parasite load following direct challenge with I. multifiliis.

The fish parasite Ichthyophthirius multifiliis – Host immunology, vaccines and novel treatments

“…The gene for Iag (IAG52B) has been inserted into the closely related ciliate Tetrahymena thermophila and successful recombinant expression was achieved [70,71] and protection in channel catfish was obtained. However, the concentration of cadmium, which was the gene promoter in the transformed T. thermophila was found to be elevated in fish tissues [72], thus posing a potential health danger.…”

Metallothionein Gene from Tetrahymena thermophila with a Copper-Inducible-Repressible Promoter

“…To date, these studies have utilized the Cd-sensitive MTT1 promoter for gene expression (11). While this promoter is a powerful tool in basic research, it requires the addition of a highly toxic metal to the growth medium, which must be disposed of during the production process (1). Clearly, the availability of alternative promoters for driving inducible expression of foreign genes in T. thermophila would be useful.…”

Evaluation of salinomycin isolated from Streptomyces albus JSY-2 against the ciliate, Ichthyophthirius multifiliis

“…The ciliate I. multifiliis is one of the most pathogenic parasites of fish, and it constitutes a major disease problem in aquaculture (McCallum, 1985(McCallum, , 1986Dickerson and Dawe, 1995;Bisharyan et al, 2003). Currently, most countries have few effective chemical treatments that can be used to control I. multifiliis (Sudová et al, 2010).…”