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ecosystem context. In so doing we also attempt to reconcile the variable ecosystem roles of
bacteria: while bacteria on particles are potential "metazoan meals", they are also in the process
of competing with metazoa for the common resource.
POM may be consumed by animals or by bacteria, or it may sink out of a given water layer.
While particle-consuming metazoa utilize POM directly, the osmotrophic bacteria can not.
Bacteria must first solubilize the particles and then take up the organic matter in the form of
monomers or sometimes oligomers. This absolute requirement for particle solubilization,
generally monomerization, imposes a mechanistic constraint on the role heterotrophic bacteria
can playas a conduit for the flow of carbon from POM. If bacteria can not exert appropriate
and sufficient "biochemical pressure" to solubilize the particles, then the other pathways of
carbon flow, namely ingestion by animals and sinking, will be favored. It is of interest to find
out whether bacteria manage to act as a significant route for carbon flow in the pathway POM -
-> DOM -- > bacteria, and if so, then what mechanisms couple POM with bacterial uptake
systems. Further, do attached (sinking) bacteria use POM in a tightly coupled manner, or does
a significant fraction of DOM leak out and is used by free-living (non-sinking) bacteria? Solving
these problems is necessary for understanding how, and how much, bacteria influence the
pathways of biogeochemical cycling of materials in the ocean's water column including the
mesopelagial.
Role of bacterial exohydrolases in parlicie solubilization and hydrolysis - uptake coupling
Bacteria solubilize particles and polymers with hydrolytic extracellular enzymes, such as
proteases and polysaccharidases (Priest, 1985; Gottschalk, 1987). The hydrolases may be
secreted (diffusible) or anchored on the cell surface (non-diffusible), and the enzymes may be
endohydrolases or exohydrolases (Gottschalk, 1987). Endohydrolases cut the particle or polymer
internally (e.g. a-amylase, an endoglucanase and serine protease, an endopeptidase) to generate
oligomers or polymers. Exohydrolases hydrolyse monomers or dimers from the end of the
polymer or suprapolymer (i.e. POM). Other hydrolases act on specific points in the polymer
structure (e.g. debranching enzyme, isoamylase). In some instances, bacteria secrete enzyme
complexes (e.g. cellulase with both an endohydrolase and an exohydrolase activity (in the case
ecosystem context. In so doing we also attempt to reconcile the variable ecosystem roles of
bacteria: while bacteria on particles are potential "metazoan meals", they are also in the process
of competing with metazoa for the common resource.
POM may be consumed by animals or by bacteria, or it may sink out of a given water layer.
While particle-consuming metazoa utilize POM directly, the osmotrophic bacteria can not.
Bacteria must first solubilize the particles and then take up the organic matter in the form of
monomers or sometimes oligomers. This absolute requirement for particle solubilization,
generally monomerization, imposes a mechanistic constraint on the role heterotrophic bacteria
can playas a conduit for the flow of carbon from POM. If bacteria can not exert appropriate
and sufficient "biochemical pressure" to solubilize the particles, then the other pathways of
carbon flow, namely ingestion by animals and sinking, will be favored. It is of interest to find
out whether bacteria manage to act as a significant route for carbon flow in the pathway POM -
-> DOM -- > bacteria, and if so, then what mechanisms couple POM with bacterial uptake
systems. Further, do attached (sinking) bacteria use POM in a tightly coupled manner, or does
a significant fraction of DOM leak out and is used by free-living (non-sinking) bacteria? Solving
these problems is necessary for understanding how, and how much, bacteria influence the
pathways of biogeochemical cycling of materials in the ocean's water column including the
mesopelagial.
Role of bacterial exohydrolases in parlicie solubilization and hydrolysis - uptake coupling
Bacteria solubilize particles and polymers with hydrolytic extracellular enzymes, such as
proteases and polysaccharidases (Priest, 1985; Gottschalk, 1987). The hydrolases may be
secreted (diffusible) or anchored on the cell surface (non-diffusible), and the enzymes may be
endohydrolases or exohydrolases (Gottschalk, 1987). Endohydrolases cut the particle or polymer
internally (e.g. a-amylase, an endoglucanase and serine protease, an endopeptidase) to generate
oligomers or polymers. Exohydrolases hydrolyse monomers or dimers from the end of the
polymer or suprapolymer (i.e. POM). Other hydrolases act on specific points in the polymer
structure (e.g. debranching enzyme, isoamylase). In some instances, bacteria secrete enzyme
complexes (e.g. cellulase with both an endohydrolase and an exohydrolase activity (in the case