48
Polymer Utilization
Dissolved proteins and polysaccharides in the euphotic zone of
the sea probably represent a quantitatively important route for matter
and energy flux into bacteriop1ankton. It is of interest, therefore,
to know the dynamics of protein and polysaccharide pools, and how
bacteria utilize these polymers. In one study, concentration of
dissolved protein off Scripps pier was found to be 950 nM (as glycine
equivalents) whi1~ the concentration of dissolved free amino acids
(DFAA) was only 23 nM (Hagstrom et a1., in press). Polysaccharide
concentrations are generally even higher than protein. Off Scripps
pier we found 2.7 ~M total carbohydrate, mostly polymeric (Hagstrom et
a1., in press). Similar values were reported by Burney et a1. (1981).
The monomeric sugars occur at much lower concentrations.
Recent work (Hollibaugh and Azam, 1983) found little dissolved
exoprotease activity in coastal surface waters; most of the activity
was associated with bacterial cells. The high metabolic cost of maintaining significant dissolved protease activity may favor hydrolysis
by cell-associated proteases. The amino acid molecules produced by
protein hydrolysis were taken up by bacteria in preference to those in
seawater suggesting a close metabolic coupling between protein
hydrolysis and amino acid uptake. Protein hydrolysis probably occurs
in the perip1asmic space of bacteria, creating high DFAA concentrations
near the transport sites. Still, a significant fraction of the
released amino acids diffuse into the seawater (Hollibaugh and Azam,
1983). It is likely that dissolved polysaccharides are utilized in a
similar fashion, although this has not been studied for planktonic
bacteria.
Utilization of Organophosphorus Compounds
Organophosphorus (OP) compounds generally do not traverse the
cell membrane, the phosphate must first be cleaved by hydrolysis. We
have found (Ammerman and Azam, unpublished) that a bacterial perip1asmic or membrane bound enzyme, 5'-nuc1eotidase, may account for a large
fraction of the OP hydrolysis in coastal waters. As in the case of
exoproteases, most of the nucleotidase activity is also associated
with the cells rather than free in seawater. Importantly, the Pi
molecules released from 5'-nuc1eotides are 10-40 times more likely to
be taken up by the microbial populations than the Pi molecules present
in the bulk-phase seawater. This preference for uptake of hydrolysis
Polymer Utilization
Dissolved proteins and polysaccharides in the euphotic zone of
the sea probably represent a quantitatively important route for matter
and energy flux into bacteriop1ankton. It is of interest, therefore,
to know the dynamics of protein and polysaccharide pools, and how
bacteria utilize these polymers. In one study, concentration of
dissolved protein off Scripps pier was found to be 950 nM (as glycine
equivalents) whi1~ the concentration of dissolved free amino acids
(DFAA) was only 23 nM (Hagstrom et a1., in press). Polysaccharide
concentrations are generally even higher than protein. Off Scripps
pier we found 2.7 ~M total carbohydrate, mostly polymeric (Hagstrom et
a1., in press). Similar values were reported by Burney et a1. (1981).
The monomeric sugars occur at much lower concentrations.
Recent work (Hollibaugh and Azam, 1983) found little dissolved
exoprotease activity in coastal surface waters; most of the activity
was associated with bacterial cells. The high metabolic cost of maintaining significant dissolved protease activity may favor hydrolysis
by cell-associated proteases. The amino acid molecules produced by
protein hydrolysis were taken up by bacteria in preference to those in
seawater suggesting a close metabolic coupling between protein
hydrolysis and amino acid uptake. Protein hydrolysis probably occurs
in the perip1asmic space of bacteria, creating high DFAA concentrations
near the transport sites. Still, a significant fraction of the
released amino acids diffuse into the seawater (Hollibaugh and Azam,
1983). It is likely that dissolved polysaccharides are utilized in a
similar fashion, although this has not been studied for planktonic
bacteria.
Utilization of Organophosphorus Compounds
Organophosphorus (OP) compounds generally do not traverse the
cell membrane, the phosphate must first be cleaved by hydrolysis. We
have found (Ammerman and Azam, unpublished) that a bacterial perip1asmic or membrane bound enzyme, 5'-nuc1eotidase, may account for a large
fraction of the OP hydrolysis in coastal waters. As in the case of
exoproteases, most of the nucleotidase activity is also associated
with the cells rather than free in seawater. Importantly, the Pi
molecules released from 5'-nuc1eotides are 10-40 times more likely to
be taken up by the microbial populations than the Pi molecules present
in the bulk-phase seawater. This preference for uptake of hydrolysis