Isolation and Characterization of a Copper Tolerant Yeast Cryptococcus sp. from the Japan Trench
Takeshi MIURA*a, Fumiyoshi ABEb, Tadashi MIZUKOSHIa, Akira INOUEb, Ron USAMIa, and Koki HORIKOSHIa,b
a Department of Applied chemistry, Faculty of Engineering, Toyo University, 2100 Kujirai, Kawagoe 350, Japan
b The DEEPSTAR Group, Japan Marine Science and Technology Center, 2-15 Natsushima- cho, Yokosuka 237, Japan
The deep-sea is an extreme environment which can be characterized by darkness, low temperature and high hydrostatic pressure. There have been many reports concerning physiological or genetic analysis of deep-sea bacteria adapted to these extreme conditions.
The problems linked to the environmental dispersion of toxic wastes are of increasing concern. Heavy metals are one of the toxic compounds which significantly affect biological activities. Bacteria and yeasts are generally the first organisms to be exposed to toxic heavy metals. We have been isolating yeasts from deep-sea sediments collected by the manned submersibles "SHINKAI 2000" and "SHINKAI 6500". To date 24 strains have been isolated from Sagami Bay (1100-1400 m depth), and 13 strains from the Japan Trench (4500-6500 m depth). Among them, a strain N6 was found to be extremely tolerant to high concentrations of copper sulfate. It was able to grow on YPD (1% yeast extract, 2% bactopeptone, 2% glucose) agar containing copper sulfate (at least 17 mM) as well as normal YPD agar. No significant reduction in growth rate was observed in YPD broth containing 10 mM copper sulfate. Similar results were obtained with copper chloride. Molecular analysis of 18S rDNA suggests that strain N6 could be a Cryptococcus sp.. IFO 0378, a type strain of Cr. albidus, scarcely grew in the presence of 10 mM copper sulfate. Several strains tested (sake yeast Saccharomyces cerevisiae or typical marine yeast Rhodotorula ingeniosa) never grew in the presence of 10 mM copper sulfate. The results suggest that the tolerance might be specific to the strain N6. We are investigating the mechanisms of this extreme tolerance to copper in strain N6, focusing on cellular metabolism, physiological conditions and protein synthesis.
