investigated the effect of trace iron conditions on the growth of these two species, as well as their response to iron sequestration by chelators. Metal analysis by ICP-MS revealed high residual concentrations (0.12 μM) of iron in the chemically defined medium used in spite of the absence of added iron and demonstrated the requirement for deferration and confirmatory trace Fe analysis. The iron contamination from other medium constituents could be successfully reduced to <0.02 μM in batch processes using an insoluble chelating resin. Cu concentrations were also significantly reduced in the extracted chemically defined medium, but significant recovery of growth could be see more achieved by supplementation of the extracted medium with Fe only. Both C. albicans and C. vini were found to require Cytoskeletal Signaling inhibitor approximately 0.5 μM added iron for complete unrestricted growth in the extracted chemically defined medium, but differed in their abilities to grow at reduced iron concentrations. The observed differences between C. albicans and C. vini were consistent with the different environments these
respective yeast species typically colonize or invade. Grape musts and wines, in which C. vini typically appears as a spoilage yeast, generally have high Fe concentrations of between 30 and 200 μM (Ough et al., 1982). The predominantly reducing environment and the low pH of grape musts and wines also favour the formation of the more soluble free ferrous species, and this Fe would be expected to have a higher bioavailability (Howard,
1999). In sharp contrast, the ecological niches that C. albicans can colonize or invade in relation to human pathogenesis are highly limiting for Fe (Weinberg, 1999). Desferrioxamine and deferiprone are two chelators used clinically very to relieve the Fe overload associated with certain human haematological disorders such as thalassaemia (Chaston & Richardson, 2003; Franchini, 2006). Desferrioxamine failed to inhibit both C. albicans and C. vini. Deferiprone did not inhibit C. vini while leading to a slightly increased lag phase in C. albicans. However, the observed differences between C. albicans and C. vini persisted in their growth response in the presence of lactoferrin. Lactoferrin is a major component of the mammalian innate immune system (Actor et al., 2009) and one of the vertebrate host defence Fe chelators, which is present in mucosal secretions (Gonzalez-Chavez et al., 2009). Lactoferrin, at the physiologically relevant concentration of 0.25 mg mL−1 and at pH 4.5, and thus, representative of the vaginal environment (Novak et al., 2007), only led to a transient inhibition of C. albicans, but inhibited the growth of C. vini over the incubation period. The results are in agreement with the lack of observed pathogenicity of C. vini and its greater susceptibility to iron restriction, while the pathogenicity of C.