Growth characteristics of the isolated
microorganism
T hiobacillus sp. CH11 was classiÐed as a chemolitho-
autotroph according to its physiological and bio-
chemical characteristics; it was motile, Gram-negative
and short-rod. The colony (diameter of 0É5È1 mm) on
the thiosulphate agar was whitish-yellow because of
extracellular deposition of sulphur. T hiobacillus sp.
CH11 grew autotrophically with elemental sulphur,
thiosulphate and sulphide, but hardly grew in faculta-
tive autotrophic and heterotrophic conditions. The
optimum pH range for the growth of T hiobacillus sp.
CH11 was 6È8. The growth pattern of T hiobacillus sp.
CH11 in the thiosulphate medium is shown in Fig. 1.
The cell numbers reached their maximum level,
108 cfu cm~3, on the Ðfth day and then rapidly
decreased on the sixth day. During the initial 6 days of
cultivation, the decrease in thiosulphate concentration
was accompanied by an increase in the cell number and
sulphate concentration. Visible elemental sulphur accu-
mulated in the medium. These results hinted that T hio-
bacillus sp. CH11 could oxidize thiosulphate to sulphate
as the Ðnal product via the accumulation of inter-
mediate sulphur. After the sixth day of cultivation, the
signiÐcant decrease in the cell number was accompanied
by an increase in sulphate concentration. It suggested
that the accumulation of sulphate was over the bu†er
capability of medium which caused the pH value and
cell number to decrease signiÐcantly. These results con-
Ðrmed that T hiobacillus sp. CH11 was sensitive to low
pH.