50
and its concentration showed diel variations in a pattern similar to
some bacterial nutrients. We found that marine bacterial assemblages
transport cAMP by a highly specific, active transport system with a
picomoplar Km. This transport system is very effective in cAMP uptake
at environmental concentrations, and can double the bacterial intracellular cAMP pool within minutes to hours (Ammerman and Azam, 1982).
We have speculated (Azam and Ammerman, 1984) that cAMP may act as
a metabolic cue in algal-bacterial interactions. The characteristics
of the cAMP transport system in bacteria indicate a regulatory rather
than a nutritional role for cAMP. The cAMP transport system shows
near-absolute specificity for cyclic nucleotides, and a preference for
cAMP. AMP,
seawater,
which
is not
occurs at about 100 times greater concentration in
a substrate of the cAMP transport system (Ammerman
It is highly unlikely that marine bacteria evolved
to take up this compound as a nutrient.
cAMP plays a
regulation of catabolic enzyme synthesis in bacteria
(Rickenberg, 1974). It is tempting to speculate that, if exuded by
the algae along with bacterial nutrients, cAMP could serve as a
unifying signal for the nutrient status of the microenvironment of the
bacterium. However, we have no direct evidence for this speculation.
and Azam, 1982) .
the cAMP system
key role in the
The fact that bacteria attack detritus but not healthy phytoplankton may have implications for the pattern of energy and matter
flow in marine planktonic foodweb.
If bacteria were to
(hydrolytically?) attack healthy phytoplankton then they would be
competing with the herbivores for algal POM, which they apparently do
not. However, algal exudation makes some of the primary production
metabolically accessible to bacterioplankton.
It may be that an
interplay of positive and negative effectors between bacteria and
phytoplankton cells regulates algal exudation and leads to a close
coupling between production and bacterial uptake of the exudates.
Clustering of bacteria around the algal cells, but without attachment,
may result from this interaction (Azam and Ammerman, 1984).
Consequences of being small and gram-negative
Planktonic marine bacteria are exceedingly small, much smaller
than the enteric bacteria which have traditionally been studied by the
bacteriologist. Most marine bacteria (in nature) are 0.2 - 0.6 ].1m in
equivalent spherical diameter (Fuhrman, 1981), hence they have a very
large surface to volume ratio.
This means that marine bacteria, per
and its concentration showed diel variations in a pattern similar to
some bacterial nutrients. We found that marine bacterial assemblages
transport cAMP by a highly specific, active transport system with a
picomoplar Km. This transport system is very effective in cAMP uptake
at environmental concentrations, and can double the bacterial intracellular cAMP pool within minutes to hours (Ammerman and Azam, 1982).
We have speculated (Azam and Ammerman, 1984) that cAMP may act as
a metabolic cue in algal-bacterial interactions. The characteristics
of the cAMP transport system in bacteria indicate a regulatory rather
than a nutritional role for cAMP. The cAMP transport system shows
near-absolute specificity for cyclic nucleotides, and a preference for
cAMP. AMP,
seawater,
which
is not
occurs at about 100 times greater concentration in
a substrate of the cAMP transport system (Ammerman
It is highly unlikely that marine bacteria evolved
to take up this compound as a nutrient.
cAMP plays a
regulation of catabolic enzyme synthesis in bacteria
(Rickenberg, 1974). It is tempting to speculate that, if exuded by
the algae along with bacterial nutrients, cAMP could serve as a
unifying signal for the nutrient status of the microenvironment of the
bacterium. However, we have no direct evidence for this speculation.
and Azam, 1982) .
the cAMP system
key role in the
The fact that bacteria attack detritus but not healthy phytoplankton may have implications for the pattern of energy and matter
flow in marine planktonic foodweb.
If bacteria were to
(hydrolytically?) attack healthy phytoplankton then they would be
competing with the herbivores for algal POM, which they apparently do
not. However, algal exudation makes some of the primary production
metabolically accessible to bacterioplankton.
It may be that an
interplay of positive and negative effectors between bacteria and
phytoplankton cells regulates algal exudation and leads to a close
coupling between production and bacterial uptake of the exudates.
Clustering of bacteria around the algal cells, but without attachment,
may result from this interaction (Azam and Ammerman, 1984).
Consequences of being small and gram-negative
Planktonic marine bacteria are exceedingly small, much smaller
than the enteric bacteria which have traditionally been studied by the
bacteriologist. Most marine bacteria (in nature) are 0.2 - 0.6 ].1m in
equivalent spherical diameter (Fuhrman, 1981), hence they have a very
large surface to volume ratio.
This means that marine bacteria, per