Deep-sea yeast strains were isolated from mud samples collected in Sagami Bay (1,100-1,400 m) and the Japan Trench (4,500-6,500 m). All of the 46 yeast isolates were capable of growth at 24°C and atmospheric pressure, suggesting that these strains might originate neritic regions or land but survived in deep sea. Based on sequencing of 26S rRNA gene, 15 strains were classified into basidiomycetous yeasts including Cryptococcus liquefaciens, Kondoa aeria, Rhodosporidium diobovatum, Rhodosporidium sphaerocarpum, Rhodotorula mucilaginosa, Rhodotorula dairenensis and Rhodotorula slooffiae, and 8 strains were classified into ascomycetous yeasts including Aureobasidium pullulans, Candida zeylanoides, Kluyveromyces nonfermentans, Metschnikowia bicuspidate and Williopsis saturnus. Screening of the 46 isolates appeared to yield a high frequency of polygalacturonase (PGase) producers capable of degrading pectin. We suggest that deep-sea yeasts are new sources of PGase producers.

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Moderately halophilic strain DT-W was isolated from the mud of the Mariana Trench. Cells of the organism were rod-shaped (1.5-2.µm x 0.5-0.8 µm) with some flagella extruding from the cells. Growth occurred in an NaCl concentration of about 0.1-15% (optimal: 3-5%), at pH of 6-9, and at temperatures ranging from 4-51°C (optimal: 30-37°C). The results of 16S rDNA analysis and DNA-DNA hybridization analyses showed that DT-W was closely related to Halomonas aquamarina, Halomonas axialensis and Halomonas meridiana. Furthermore, additional physiological properties and the cytochrome contents of DT-W were also analyzed.

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