51
unit biomass, have a large membrane area for the locationzation of the
enzymes which hydrolyse polymers and the transport systems which take
up the resulting monomers. This large surface to volume ratio in
marine bacteria therefore should provide an intimate metabolic contact
with the organic matter in the environment.
Host marine bacteria are gram-negative, and hence they have a
periplasmic space. The periplasmic space is a region between the
outer membrane and the plasmalemma of the gram-negative bacteria,
containing a number of enzymes and solute binding proteins. The periplasmic enzymes have a function in hydrolysis of polymers and OP
compounds, while the binding proteins, presumably free in the
periplasmic space, may have a role in solute transport. The periplasmic space in enteric bacteria Salmonella typhimurium and
Escherichia coli is estimated to occupy 20-40% of the cell volume
(Stock et al., 1977). If the thickness of the periplasmic space in
marine bacteria is the same as in the enterics then (because of the
small diameter of marine bacteria) the periplasmic space might
occupy an even greater percent of the cell volume.
If these periplasmic proteins assist in nutrient aquisition, then gram-negative
bacteria may be better adapted than gram-positive bacteria to the
dilute and fluctuating nutrient levels encountered in seawater.
Several interesting metabolic consequences result from the extremely
small size of marine bacterioplankton, especially those at the lower
end of the size spectrum. A 0.2 llm diameter bacterium has a cell
volume of merely 0.0033 llm 3 or 3.33 x 10-lB~. If this cell took up
one molecule (1.66 x 10-24 mo l es )ofanamino acid, the intracellular
concentration of that amino acid would increase by 0.54 x 10-6M,
which is 100 to 100Q-fold the concentration of individual amino acids
in the bulk-phase seawater. When one considers that a significant
fraction of the cell volume is occupied by the periplasmic space,
then the increase in the intracellular concentration per molecule
would be even greater than 0.54 llM. This means that uptake from
bulk-phase seawater of solutes such as amino acids will always be
against concentration gradients, and hence must be energy-dependent.
It also follows that the uptake of a very few effector molecules per
cell could profoundly affect the metabolic regulation. The intracellular concentration of cAMP is on the order of 1 llM (Ammerman and
Azam, 1982 and references therein), which for the very small marine
bacteria corresponds to only 1 or 2 molecules per cell.
unit biomass, have a large membrane area for the locationzation of the
enzymes which hydrolyse polymers and the transport systems which take
up the resulting monomers. This large surface to volume ratio in
marine bacteria therefore should provide an intimate metabolic contact
with the organic matter in the environment.
Host marine bacteria are gram-negative, and hence they have a
periplasmic space. The periplasmic space is a region between the
outer membrane and the plasmalemma of the gram-negative bacteria,
containing a number of enzymes and solute binding proteins. The periplasmic enzymes have a function in hydrolysis of polymers and OP
compounds, while the binding proteins, presumably free in the
periplasmic space, may have a role in solute transport. The periplasmic space in enteric bacteria Salmonella typhimurium and
Escherichia coli is estimated to occupy 20-40% of the cell volume
(Stock et al., 1977). If the thickness of the periplasmic space in
marine bacteria is the same as in the enterics then (because of the
small diameter of marine bacteria) the periplasmic space might
occupy an even greater percent of the cell volume.
If these periplasmic proteins assist in nutrient aquisition, then gram-negative
bacteria may be better adapted than gram-positive bacteria to the
dilute and fluctuating nutrient levels encountered in seawater.
Several interesting metabolic consequences result from the extremely
small size of marine bacterioplankton, especially those at the lower
end of the size spectrum. A 0.2 llm diameter bacterium has a cell
volume of merely 0.0033 llm 3 or 3.33 x 10-lB~. If this cell took up
one molecule (1.66 x 10-24 mo l es )ofanamino acid, the intracellular
concentration of that amino acid would increase by 0.54 x 10-6M,
which is 100 to 100Q-fold the concentration of individual amino acids
in the bulk-phase seawater. When one considers that a significant
fraction of the cell volume is occupied by the periplasmic space,
then the increase in the intracellular concentration per molecule
would be even greater than 0.54 llM. This means that uptake from
bulk-phase seawater of solutes such as amino acids will always be
against concentration gradients, and hence must be energy-dependent.
It also follows that the uptake of a very few effector molecules per
cell could profoundly affect the metabolic regulation. The intracellular concentration of cAMP is on the order of 1 llM (Ammerman and
Azam, 1982 and references therein), which for the very small marine
bacteria corresponds to only 1 or 2 molecules per cell.