The dissolved oxygen level in the culture medium was de-
termined by OH-113 type"Mini-Digi"equipment(Radelkis,
Hungary)which measured the relative oxygen saturation in the
medium.The absolute oxygen concentration was calculated us-
Table 1.Composition of culture medium for yeast growth
(g/L)
glucose 70.0
(NH4)2SO4 6.5
KH2PO4 2.5
MgSO4.7H20 1.7
yeast extract 5.0
(mg/L)
CaCl~.2H20 150.0
FeC13-.6H20 50.0
ZnSO4.7H20 30.0
MnSO4.2H~O 30.0
C u S Q.5H~O 5.0
CoCI2.6H20 2.0
H3PO~1.0
desthi~obiotin 0.5
ing the dependence of saturation on temperature,taking into
consideration the dissolved organic material and salt content:
Temperature of cultivation:30°C
Atmospheric pressure:101.3 kPa(no fluctuation assumed)
Calculation of absolute dissolved oxygen concentration
(Cx):
for organic material:Cx~=CT(relative saturation%/100%)(1-0,012 Ca)
for inorganic salts:Cx~=CT(relative saturation%/100%)(1-0.048 C a~)t
C=Cr(relative saturation%/100%)(1-0.012 Ca)(1-0.048 C it)
CT:oxygen content of air-saturated water at 30°C(rag/L)
relative saturation%:measured oxygen saturation in culture
medium
C au:salt concentration in per cent of culture medium
Ca:organic material concentration in per cent of culture medi-
um(constants were given by the manufacturer)
The Se content of the nutrient broth and the dried yeast sam-
ples was determined by the Inductive-Coupled Plasma Atomic
Emission System(ICP-AES).The dried yeast samples were
prepared for analysis as follows:0.5 g yeast samples,were put
into an acid-resistant Teflon digestion container.The digestion
of the samples was performed with 3 mL HNO 3+3 mL H~O2
and the samples were allowed to stand overnight at room tem-
perature,then boiled at 100 oC 30 min.After cooling,the sam-
ples were diluted up to i0 mL with 2x distilled water.
For determination of the Se incorporation into yeast cells
the biomass was sonicated.1 g of the dried yeast powder was
suspended in 10 mL phosphate buffer(pH=6.0)and the cells
were disrupted in an ULTRASONIC homogenizer(Braun,300
W,T=30°C)3 times,each for 3 min.The suspension contain-
ing disrupted cells was then stored at-24°C.Before ICP-AES
measurement the thawed samples were centrifuged 15000 x g
for 30 rain.After separation of the supernatant from cell frag-
ments,0.2 mL 3%trichloro-acetic acid was added to the solu-
tion(10 mL)and the precipitated proteins were removed by ill-
tration(GF-5 glassfilter,Macherey-Nagel).The filtrate and
dried celI fragments were then analysed.