Abstract Zinc is one of the most important trace elements and deficiency can lead to significant clinical complications. Microbial transformation is one of the most important methods used to supplement organic zinc and there may be some naturally occurring microorganisms that have both higher zinc tolerances and transformation capabilities. In this study, microorganisms which displayed such characteristics were widely screened, and a strain designated T-A was found. Morphological and molecular determination demonstrated that T-A is closely related to Candida tropicalis with 87% of 18S rDNA homology, with a G+C content measured by RP-HPLC of 88.42%. Candida tropicalis sp. T-A strains were shown to grow and transform zinc best at pH5 in medium with a zinc ion concentration of 8000 μg/mL at 28 °C for 121 hours. Our results showed C. tropicalis sp. T-A’s zinc content was 19.153 mg/g dry weight, with a relative bioavailability in rats of 173% when compared with traditional zinc supplements. Our study suggests that C. tropicalis sp. T-A could be exploited for use as a potential zinc supplement.

Iron is an essential element for nearly all living organisms, and its deficiency is the most common form of malnutrition in the world. The organic forms of trace elements are considered more bioavailable than the inorganic forms. Although Saccharomyces cerevisiae can enrich metal elements and convert inorganic iron to organic species, its tolerability and transforming capacity are limited. The aim of this study was to screen higher biomass and other iron-enriched fungi strains besides Saccharomyces cerevisiae from the natural environment. A PDA medium containing 800 μg/mL iron was used for initial screening. Fifty strains that tolerated high iron concentration were isolated from the natural environment, and only one strain, No.BY1109, grew well at Fe (II) concentration of 10,000μg/ml. According to morphological characterization, 18S rDNA sequence analysis, and biophysical and biochemical characterization, the strain No.BY1109 was identified as Rhodotorula. The iron content of No.BY1109 (10 mg Fe/g dry cell) was determined using atomic absorption spectrometry. The results of distribution of iron in the cells showed that iron ion was mainly chelated in the cell walls and vacuoles. The bioavailability in rats confirmed that strain No.BY1109 had higher absorption efficiency than that of ferrous sulfate after single dose oral administration. The present study introduces new iron supplements, and it is a basis for finding new iron supplements from natural environment.