In order to investigate the barotolerance of marine fungi and to
elucidate their ecological role in the deep sea, high-pressure
equipment was built and tested. Cultures of the marine yeasts Debaryomyces
hansenii, Rhodotorula rubra and Rhodosporidium
sphaerocarpum were inoculated into gas-permeable plastic foil bags
and
incubated in pressure vessels filled with hydraulic fluid that
serves also as an oxygen reservoir. The equipment was used at temperatures
from 7° to 34°C and pressures from 0·1 to 80·0 MPa.
Comparison of five types of plastic foil showed effects on total cell number
in
batch culture. An exchange of the hydraulic fluid
increased yield by replenishing oxygen, the growth-limiting factor. There
were no detectable growth differences between buffered
(TRIS, HEPES, imidazole, MES) and unbuffered media and thus unbuffered
medium
was used. Yeasts were best cultivated in an
unbuffered sea-water medium (glucose–peptone–yeast extract)
sealed in bags made from polyethylene foil. The fluorocarbon liquid
FC-77 provided the best oxygen reservoir owing to its high oxygen and carbon
dioxide solubility. An exchange of the hydraulic
fluid is not necessary if sensitive growth determination methods are used.
All
marine yeasts cultivated under simulated deep sea
conditions were able to grow at least up to a pressure of 20 MPa, with
Rhodotorula rubra and Rhodosporidium sphaerocarpum growing
at 40 MPa, corresponding to 4000 m depth. Thus, marine yeasts are able
to
grow under simulated deep sea conditions and may
participate in the degradation of organic matter in the deep sea.