64
GORDON A.:RILEY
by Kriss (1963) in various deep water situations. The values obtained
by these authors are similar to the estimated population of Pseudomonas
during the stable phase after the early maximum, suggesting that the
balance between living and non-living fractions in these experiments is
essentially similar to that which occurs in the sea.
Plate counts were made during the experiments involving long term
storage of deep water and in two of the three experiments summarized
in Table V. The third experiment in Table V, involving continuous
circulation and a 20% cropping rate, was not monitored.
These experiments included inoculation with Pseudomonas, inoculation with raw sea water, and simple filtration with no additions, but
in all cases results were essentially the same, differing only in minor
details of timing and relatively insignificant variations in population
level. The early maximum was observed in some experiments and not
in others, as indicated in the earlier account of carbon concentrations.
There was a stable phase with populations of the order of lo4 cells/ml,
more or less, which was approximately the same as in short term
Pseudomonas experiments described earlier. This persisted for 2-4
weeks, and then the plate counts began to increase steadily. The
number of dilutions required for suitable counts had to be increased.
Errors were suspected, and the water used for dilution was examined
frequently and found to be negative. The increase continued to the
end of experiments lasting 17 weeks, and the concentration at that time
was of the order of 10" cells/ml or more.
No good reason has been found to reject the plate counts. On the
other hand, the quantity of bacteria found, if they had a " typical "
carbon content of 4 x 10-7 pglcell, would total 0.4-1 mg C/litre. This
is about an order of magnitude higher than the total carbon that was
demonstrated to be present. Moreover, visual examination gave no
indication of a marked increase in bacteria. Careful microscopic counts
were not attempted but any such increase would be clearly evident.
If the plate counts are valid, the bacteria would have to be small
enough t o be unrecognized as such in these examinations and of a size
to permit their total carbon content to fall within reasonable limits.
This probably means a size range of 0.2-0.4 p for much of the p o p -
lation.
There is a common impression that most marine bacteria are of the
order of 1-3 p (ZoBell, 1946). However, water that has passed through
0-45 p filters is almost never sterile, and the most rigorous precautions
do not always prevent growth in water that has gone through 0.22 p
filters. Later examination of such filtrates commonly shows the
presence of bacteria that are too large to pass through the filters.
GORDON A.:RILEY
by Kriss (1963) in various deep water situations. The values obtained
by these authors are similar to the estimated population of Pseudomonas
during the stable phase after the early maximum, suggesting that the
balance between living and non-living fractions in these experiments is
essentially similar to that which occurs in the sea.
Plate counts were made during the experiments involving long term
storage of deep water and in two of the three experiments summarized
in Table V. The third experiment in Table V, involving continuous
circulation and a 20% cropping rate, was not monitored.
These experiments included inoculation with Pseudomonas, inoculation with raw sea water, and simple filtration with no additions, but
in all cases results were essentially the same, differing only in minor
details of timing and relatively insignificant variations in population
level. The early maximum was observed in some experiments and not
in others, as indicated in the earlier account of carbon concentrations.
There was a stable phase with populations of the order of lo4 cells/ml,
more or less, which was approximately the same as in short term
Pseudomonas experiments described earlier. This persisted for 2-4
weeks, and then the plate counts began to increase steadily. The
number of dilutions required for suitable counts had to be increased.
Errors were suspected, and the water used for dilution was examined
frequently and found to be negative. The increase continued to the
end of experiments lasting 17 weeks, and the concentration at that time
was of the order of 10" cells/ml or more.
No good reason has been found to reject the plate counts. On the
other hand, the quantity of bacteria found, if they had a " typical "
carbon content of 4 x 10-7 pglcell, would total 0.4-1 mg C/litre. This
is about an order of magnitude higher than the total carbon that was
demonstrated to be present. Moreover, visual examination gave no
indication of a marked increase in bacteria. Careful microscopic counts
were not attempted but any such increase would be clearly evident.
If the plate counts are valid, the bacteria would have to be small
enough t o be unrecognized as such in these examinations and of a size
to permit their total carbon content to fall within reasonable limits.
This probably means a size range of 0.2-0.4 p for much of the p o p -
lation.
There is a common impression that most marine bacteria are of the
order of 1-3 p (ZoBell, 1946). However, water that has passed through
0-45 p filters is almost never sterile, and the most rigorous precautions
do not always prevent growth in water that has gone through 0.22 p
filters. Later examination of such filtrates commonly shows the
presence of bacteria that are too large to pass through the filters.