PARTICULATE ORGANIC MATTER IN SEA WATER
63
monas that was used as an artificial inoculum had been grown in the
laboratory for some months and had demonstrated that it was one of
the species that thrives under such conditions. Hence there is little
reason to doubt that it could be monitored by plate counts with a fair
degree of accuracy.
If these counts are accepted as realistic they can be used to evaluate
the biomass of bacteria in relation to total particulate carbon. HolmHansen and Booth (1966) estimated that average carbon content of
bacteria is about 4 x 1 0 - 7 pglcell, and rough computations based on
the measured volume of Pseudomonas suggest that this is a reasonable
value to use for present purposes. Thus the largest observed population
of 87 x 103 cells/ml should contain about 35 pg C/litre, and in the later
period after the maximum, an average figure would be about 3pg.
Thus the living fraction would appear to be less than one-tenth of total
particulate carbon at all times, and to anyone who has examined the
material visually, this is not an unreasonable conclusion. Earlier estimates of 20%, based on direct carbon analysis, possibly are too large,
for the inoculum contained some non-living flocculated material.
There is a possibility that these figures represent a slight underestimate on the grounds that the Pseudomonas inoculum probably was
contaminated by the growth of adventitious bacteria introduced by the
filtering process, and some of these may not have been susceptible to
detection by plating methods. However, the experiments themselves
impose a selective process for bacteria which can grow at room temperature, and in the absence of an artificial inoculum the plate counts for
such bacteria were half as large at the time of the maximum as in the
Pseudomonas experiments. If the difference had been an order of
magnitude or more, the possibility of the existence of a large undetected
population would seem more likely.
The paper by Holm-Hansen and Booth (1966) which was cited
above was particularly concerned with the development of a method
for measuring adenosine triphosphate (ATP) and using it to determine
relative proportions of living and non-living particulate organic matter.
They established the fact that ATP disintegrates almost instantly upon
death of the organisms, and the concentration varied within reasonably
narrow limits in various organisms examined, so that the method
appeared to be thoroughly suitable for its intended purpose. I n deep
water, where bacteria are believed to constitute the major living component, the method was used to estimate the number of viable bacteria.
The average for the depth range of 183-1 025 m at a station off the
California coast was 6 x 103 cells/ml, and the authors pointed out
that these results were in good agreement with direct counts reported
63
monas that was used as an artificial inoculum had been grown in the
laboratory for some months and had demonstrated that it was one of
the species that thrives under such conditions. Hence there is little
reason to doubt that it could be monitored by plate counts with a fair
degree of accuracy.
If these counts are accepted as realistic they can be used to evaluate
the biomass of bacteria in relation to total particulate carbon. HolmHansen and Booth (1966) estimated that average carbon content of
bacteria is about 4 x 1 0 - 7 pglcell, and rough computations based on
the measured volume of Pseudomonas suggest that this is a reasonable
value to use for present purposes. Thus the largest observed population
of 87 x 103 cells/ml should contain about 35 pg C/litre, and in the later
period after the maximum, an average figure would be about 3pg.
Thus the living fraction would appear to be less than one-tenth of total
particulate carbon at all times, and to anyone who has examined the
material visually, this is not an unreasonable conclusion. Earlier estimates of 20%, based on direct carbon analysis, possibly are too large,
for the inoculum contained some non-living flocculated material.
There is a possibility that these figures represent a slight underestimate on the grounds that the Pseudomonas inoculum probably was
contaminated by the growth of adventitious bacteria introduced by the
filtering process, and some of these may not have been susceptible to
detection by plating methods. However, the experiments themselves
impose a selective process for bacteria which can grow at room temperature, and in the absence of an artificial inoculum the plate counts for
such bacteria were half as large at the time of the maximum as in the
Pseudomonas experiments. If the difference had been an order of
magnitude or more, the possibility of the existence of a large undetected
population would seem more likely.
The paper by Holm-Hansen and Booth (1966) which was cited
above was particularly concerned with the development of a method
for measuring adenosine triphosphate (ATP) and using it to determine
relative proportions of living and non-living particulate organic matter.
They established the fact that ATP disintegrates almost instantly upon
death of the organisms, and the concentration varied within reasonably
narrow limits in various organisms examined, so that the method
appeared to be thoroughly suitable for its intended purpose. I n deep
water, where bacteria are believed to constitute the major living component, the method was used to estimate the number of viable bacteria.
The average for the depth range of 183-1 025 m at a station off the
California coast was 6 x 103 cells/ml, and the authors pointed out
that these results were in good agreement with direct counts reported