YEASTS FROM THE PACIFIC OCEAN

Abstract

Ecological survey of yeasts was conducted during the cruise of KH-67-5, by the research vessel Hakuho-Maru of Ocean Research Institute, University of Tokyo, along Long. 150°E from Lat. 44°N to the equator in the Pacific Ocean in December, 1967. Yeasts were detected from the surface to a depth of 4, 000m. Of 184 seawater samples, 27.7% were positive for yeasts. The average number of yeasts detected in 1 liter of seawater was 56.7 for yeast-positive samples and 15.7 for total samples.
Isolated yeast strains were identified as strains belonging to the genera of Rhodotorula, Cryptococcus, Debaryomyces, and Candida.
The effects of salt concentration, temperature, pH, and hydrostatic pressure on the growth of selected strains were studied for the assessment of the possibility whether the reproduction of marine-occurring yeasts is actual or not in the environment in situ. Maximum NaCl tolerance ranged from 9 to 21%, exhibiting fairly good growth at NaCl concentration of seawater. The pH threshold for growth on alkaline range overlapped with the pH range of seawater. The pH 8.1, a widely observed pH in the sea, was deleterious for most of the strains. It was suggested that marine yeasts may be subjected to extensive pH effects by different bodies of seawater. The maximum tolerance to increased hydrostatic pressure observed among the strains was 400 to 500 atm, which corresponds to a depth of 4, 000 to 5, 000m. It was suggested from the pressure experiments that for the growth of most marine yeasts hydrostatic pressure is not so exacting until the depth reaches 2, 000m, and its adverse effect increases with depth and are remarkable at the depth of 4, 000m or more. Though marine-occurring yeasts seemed to be more tolerant to hydrostatic pressure than terrestrial yeasts, no clear relationship could be found between the tolerance and the depth from which they were isolated.