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It is customary to distinguish between the dissolved and particulate organic matter pools in
seawater on the basis of filterability. However, recent reports show that abundant colloidal
particles span the size-range between the dissolved and the particulate phases (Koike et al.,
1990). For the purpose of understanding the interactions of bacteria with the organic matter, it
is useful to think of the organic matter pool as a continuum, containing concentration gradients
but no rigid demarcations between phytoplankton, detritus and dissolved polymers. In this view,
macromolecules emanating from the cell surface or from dissolving detritus particles merge and
mingle with the macromolecules in solution thus creating a polymer field. Phytoplankton cells,
especially under nutrient limitation, secrete polysaccharides or mucopolysaccharides (Mykelstad,
1977) which may have the characteristics of a gel. As one moves away from the surface of the
phytoplankton cell and into the surrounding water, the polymeric matrix in the seawater would
become less concentrated and less viscous. One might even hypothesize that bacteria use
viscosity gradients to sense their environment and respond by making "metabolic decisions"
(Belas et al., 1986).
This view emphasizes the role of polymers in the spaces between particulate loci. We now know
that the concentration (w/v) of polymeric utilizable dissolved organic matter (UDOM) such as
protein, polysaccharides, DNA and RNA is roughly an order of magnitude higher than the
corresponding monomer pools. Using literature values of the concentration of these polymers
in seawater, we calculated, assuming one linear molecule for each pool, the length of DNA,
protein, and polysaccharide to be on the order of 2, 310, and 5600 km mtl, respectively! This
is equivalent to a one centimeter cube of seawater being criss-crossed 10 5 - 10 8 times by each
of the polymers, creating a polymer meshwork. We are not implying that each polymer pool is
composed of a single molecule, and the molecules are certainly folded and branched to some
extent, but the calculations give an impression of the intricacy of the matrix with which bacteria
interact. Metabolic interactions of bacteria with the polymeric substrates would involve
hydrolytic cleavage (discussed later), altering the structure of the matrix.
It is customary to distinguish between the dissolved and particulate organic matter pools in
seawater on the basis of filterability. However, recent reports show that abundant colloidal
particles span the size-range between the dissolved and the particulate phases (Koike et al.,
1990). For the purpose of understanding the interactions of bacteria with the organic matter, it
is useful to think of the organic matter pool as a continuum, containing concentration gradients
but no rigid demarcations between phytoplankton, detritus and dissolved polymers. In this view,
macromolecules emanating from the cell surface or from dissolving detritus particles merge and
mingle with the macromolecules in solution thus creating a polymer field. Phytoplankton cells,
especially under nutrient limitation, secrete polysaccharides or mucopolysaccharides (Mykelstad,
1977) which may have the characteristics of a gel. As one moves away from the surface of the
phytoplankton cell and into the surrounding water, the polymeric matrix in the seawater would
become less concentrated and less viscous. One might even hypothesize that bacteria use
viscosity gradients to sense their environment and respond by making "metabolic decisions"
(Belas et al., 1986).
This view emphasizes the role of polymers in the spaces between particulate loci. We now know
that the concentration (w/v) of polymeric utilizable dissolved organic matter (UDOM) such as
protein, polysaccharides, DNA and RNA is roughly an order of magnitude higher than the
corresponding monomer pools. Using literature values of the concentration of these polymers
in seawater, we calculated, assuming one linear molecule for each pool, the length of DNA,
protein, and polysaccharide to be on the order of 2, 310, and 5600 km mtl, respectively! This
is equivalent to a one centimeter cube of seawater being criss-crossed 10 5 - 10 8 times by each
of the polymers, creating a polymer meshwork. We are not implying that each polymer pool is
composed of a single molecule, and the molecules are certainly folded and branched to some
extent, but the calculations give an impression of the intricacy of the matrix with which bacteria
interact. Metabolic interactions of bacteria with the polymeric substrates would involve
hydrolytic cleavage (discussed later), altering the structure of the matrix.