228
of cellulase, endo-13-(I--> 4)-glucanase to internally cut the polymer and exo-B-(1-->4)
glucanase to release dimers from the non-reducing end of the oligomers). The point we wish to
make is that there is a varied repertoire of hydrolases with which bacteria can attack most
biogenic particles and polymers to hydrolyse them into transportable molecules.
Attack by endohydrolases may cause loose hydrolysis-uptake coupling since polymers are
generated which must still be acted upon by exohydrolases to generate transportable monomers
and oligomers. Exohydrolases, on the other hand, should cause tighter hydrolysis-uptake
coupling (Hollibaugh and Azam, 1983). In a biogeochemical context it is important whether or
not attached bacteria tightly couple paM solubilization with uptake of the liberated DaM. If
they do, then paM will be solubilized and respired by the attached bacteria which will sink
along with the particle. If particle solubilization and DaM uptake are loosely coupled or
uncoupled, then DaM will diffuse to the non-sinking free-living bacteria. Thus, the nature of
coupling between paM and attached bacteria could produce quite different biogeochemical
scenarios of carbon flow. We should therefore find out whether or not attached bacteria tightly
couple paM hydrolysis with DaM uptake and whether flux into attached bacteria is a significant
pathway for carbon flow.
Carbon flow from POM to the free-living bacteria
Several studies have measured carbon demand of particle-attached bacteria, and on that basis
calculated whether bacteria were important in particle decomposition (Kirchman, 1983; Hoppe,
1984; Ducklow et al., 1985; Alldredge and Youngbluth, 1985; Jacobsen and Azam, 1984).
These studies concluded that attached bacteria grow too slowly to account for significant pac
decomposition. Karl et al. (1988) concluded that sinking particles were actually unsuitable
habitats for bacterial growth. Cho and Azam (1988) determined carbon demand of both attached
and free-living bacteria in the mesopelagic zones of 2 Pacific Ocean sites. While attached
bacteria were responsible for minor carbon demand (in consonance with the above mentioned
studies) the carbon demand of free-living bacteria was so substantial that it could account for
80% or more of the depth-dissipation of sinking POc. Most bacteria in the mesopelagial were
free-living and over 90% of total bacterial carbon demand was due to these (operationally
of cellulase, endo-13-(I--> 4)-glucanase to internally cut the polymer and exo-B-(1-->4)
glucanase to release dimers from the non-reducing end of the oligomers). The point we wish to
make is that there is a varied repertoire of hydrolases with which bacteria can attack most
biogenic particles and polymers to hydrolyse them into transportable molecules.
Attack by endohydrolases may cause loose hydrolysis-uptake coupling since polymers are
generated which must still be acted upon by exohydrolases to generate transportable monomers
and oligomers. Exohydrolases, on the other hand, should cause tighter hydrolysis-uptake
coupling (Hollibaugh and Azam, 1983). In a biogeochemical context it is important whether or
not attached bacteria tightly couple paM solubilization with uptake of the liberated DaM. If
they do, then paM will be solubilized and respired by the attached bacteria which will sink
along with the particle. If particle solubilization and DaM uptake are loosely coupled or
uncoupled, then DaM will diffuse to the non-sinking free-living bacteria. Thus, the nature of
coupling between paM and attached bacteria could produce quite different biogeochemical
scenarios of carbon flow. We should therefore find out whether or not attached bacteria tightly
couple paM hydrolysis with DaM uptake and whether flux into attached bacteria is a significant
pathway for carbon flow.
Carbon flow from POM to the free-living bacteria
Several studies have measured carbon demand of particle-attached bacteria, and on that basis
calculated whether bacteria were important in particle decomposition (Kirchman, 1983; Hoppe,
1984; Ducklow et al., 1985; Alldredge and Youngbluth, 1985; Jacobsen and Azam, 1984).
These studies concluded that attached bacteria grow too slowly to account for significant pac
decomposition. Karl et al. (1988) concluded that sinking particles were actually unsuitable
habitats for bacterial growth. Cho and Azam (1988) determined carbon demand of both attached
and free-living bacteria in the mesopelagic zones of 2 Pacific Ocean sites. While attached
bacteria were responsible for minor carbon demand (in consonance with the above mentioned
studies) the carbon demand of free-living bacteria was so substantial that it could account for
80% or more of the depth-dissipation of sinking POc. Most bacteria in the mesopelagial were
free-living and over 90% of total bacterial carbon demand was due to these (operationally