In deep-sea samples from depths of between 2 770 and 4 775 m, viable counts were low, 70
to 14 000 cells/ ml of wet sediment, and about the same for both incubation temperatures.
However, different types of bacteria were isolated dependent on the incubation temperature applied. The majority of the isolates from the 2°C plates were Gram-negative, but
most of the 20°C isolates belonged to the Gram-positive type (Fig. 2).
The majority of the deep-sea isolates from the 2°C plates were extremely psychrophilic.
Their optimal growth temperatures were about 4°C (Fig. 3) and their maximal growth
temperatures ranged from 4 to 12°C (Fig. 4).
Figure 4 : Maximal growth temperatures of deep-sea bacteria, isolated from 2°C
plates.
DISCUSSION
In the past, incubation temperatures of about 20°C have been used to determine numbers
of culturable bacteria in the sea. The majority of deep-sea sediment bacteria, isolated
from 20°C plate cultures, belonged to the Gram-positive type (Riiger, 1973 ; Bensoussan
et al., 1979, 1981). Corresponding results were obtained from surface sediment samples of
the eastern tropical Atlantic (Fig.2). Most of the Gram-positive isolates are mesophilic,
did not grow at 4°C within six weeks, and were able to grow in freshwater media
(unpublished data). Since these organisms are not adapted to low temperatures, they are
probably not indigenous to the deep-sea environment.
On the other hand, most of the deep-sea isolates from 2°C plates are Gram-negative and
psychrophilic. The maximal growth temperatures for 75 strains from the topmost sediment layers were between 4 and 12°C, for 19 strains between 12 and 18°C, and for 9 strains
between 18 and 24°C. Only 25 strains were able to grow at 24°C. The results demonstrate
that it is essential to use in situ temperatures for the isolation of native deep-sea bacteria,
as already discussed by Yayanos and Dietz (1982), and that psychrophiles occur abundantly in marine sediments, not only in the polar regions, but also elsewhere in the sea.
ACKNOWLEDGEMENTS
I am grateful to Ch. Summa for excellent technical assistance and to T.L. Tan and M.J. Gomez for critical
reading of the manuscript and for correcting the English text.
100
to 14 000 cells/ ml of wet sediment, and about the same for both incubation temperatures.
However, different types of bacteria were isolated dependent on the incubation temperature applied. The majority of the isolates from the 2°C plates were Gram-negative, but
most of the 20°C isolates belonged to the Gram-positive type (Fig. 2).
The majority of the deep-sea isolates from the 2°C plates were extremely psychrophilic.
Their optimal growth temperatures were about 4°C (Fig. 3) and their maximal growth
temperatures ranged from 4 to 12°C (Fig. 4).
Figure 4 : Maximal growth temperatures of deep-sea bacteria, isolated from 2°C
plates.
DISCUSSION
In the past, incubation temperatures of about 20°C have been used to determine numbers
of culturable bacteria in the sea. The majority of deep-sea sediment bacteria, isolated
from 20°C plate cultures, belonged to the Gram-positive type (Riiger, 1973 ; Bensoussan
et al., 1979, 1981). Corresponding results were obtained from surface sediment samples of
the eastern tropical Atlantic (Fig.2). Most of the Gram-positive isolates are mesophilic,
did not grow at 4°C within six weeks, and were able to grow in freshwater media
(unpublished data). Since these organisms are not adapted to low temperatures, they are
probably not indigenous to the deep-sea environment.
On the other hand, most of the deep-sea isolates from 2°C plates are Gram-negative and
psychrophilic. The maximal growth temperatures for 75 strains from the topmost sediment layers were between 4 and 12°C, for 19 strains between 12 and 18°C, and for 9 strains
between 18 and 24°C. Only 25 strains were able to grow at 24°C. The results demonstrate
that it is essential to use in situ temperatures for the isolation of native deep-sea bacteria,
as already discussed by Yayanos and Dietz (1982), and that psychrophiles occur abundantly in marine sediments, not only in the polar regions, but also elsewhere in the sea.
ACKNOWLEDGEMENTS
I am grateful to Ch. Summa for excellent technical assistance and to T.L. Tan and M.J. Gomez for critical
reading of the manuscript and for correcting the English text.
100