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should be seen as a consequence of what bacteria, as species with specific biochemical
adaptations and evolutionary history, must do to persist in the pelagic ocean environment. The
need to focus on the microenvironment is all but obvious, given that bacteria live, grow and die
in microenvironments.
ORGANIC MATTER IN THE ENVIRONMENTS OF BACTERIA
In order to develop a unified concept of bacteria-organic matter interactions, and in keeping with
our focus on biochemical adaptations, we seek to develop a view of organic matter which is
based on what the bacterium "sees" in its environment. Bacteria respond to generalized
physicochemical signals and search images and do not make a distinction per se between living
and dead materials. Bacteria might metabolically (e.g. with enzymes) attack phytoplankton just
as they attack detritus (unless phytoplankton can defend themselves; Pomeroy and Wiebe, 1988).
Phytoplankton, detritus, colloids and DOM can be considered as creating an organic matter field
within which bacteria operate to optimize survival and persistence. Predators of bacteria
(protozoa on free-living and metazoa on attached bacteria) within the organic matter field may
further modify the strategies of bacteria to optimize survival and persistence.
In the euphotic zone, a bacterium is within 100s of Jlm from the nearest phytoplankton (Azam
and Ammerman, 1984) and even closer to a detritus particle. Chemotaxis has been demonstrated
in marine isolates (Chett and Mitchell, 1976; Paerl and Gallucci, 1985) and natural assemblage
(discussed in Azam and Ammerman, 1984; Cho, 1988) although only a small fraction of
bacterial assemblages may be chemotactic at any given time (5-35 %; Cho, 1988). Swimming
speeds in natural assemblages in one observation were on the order of 30 Jlm sec· l (Ammerman
and Azam, 1984). Cells may also become clustered as a result of turbulence and sheer,
independent of biological mechanisms (Mitchell et at., 1990). So, bacteria are quite close to the
particulate loci of organic matter, and it would be surprising indeed if they did not interact with
them. Also, the intervening space contains colloids and polymers which may, in part, be
sloughing off from the surfaces of phytoplankton and detritus (below), and with which bacteria
may also interact along the way.
should be seen as a consequence of what bacteria, as species with specific biochemical
adaptations and evolutionary history, must do to persist in the pelagic ocean environment. The
need to focus on the microenvironment is all but obvious, given that bacteria live, grow and die
in microenvironments.
ORGANIC MATTER IN THE ENVIRONMENTS OF BACTERIA
In order to develop a unified concept of bacteria-organic matter interactions, and in keeping with
our focus on biochemical adaptations, we seek to develop a view of organic matter which is
based on what the bacterium "sees" in its environment. Bacteria respond to generalized
physicochemical signals and search images and do not make a distinction per se between living
and dead materials. Bacteria might metabolically (e.g. with enzymes) attack phytoplankton just
as they attack detritus (unless phytoplankton can defend themselves; Pomeroy and Wiebe, 1988).
Phytoplankton, detritus, colloids and DOM can be considered as creating an organic matter field
within which bacteria operate to optimize survival and persistence. Predators of bacteria
(protozoa on free-living and metazoa on attached bacteria) within the organic matter field may
further modify the strategies of bacteria to optimize survival and persistence.
In the euphotic zone, a bacterium is within 100s of Jlm from the nearest phytoplankton (Azam
and Ammerman, 1984) and even closer to a detritus particle. Chemotaxis has been demonstrated
in marine isolates (Chett and Mitchell, 1976; Paerl and Gallucci, 1985) and natural assemblage
(discussed in Azam and Ammerman, 1984; Cho, 1988) although only a small fraction of
bacterial assemblages may be chemotactic at any given time (5-35 %; Cho, 1988). Swimming
speeds in natural assemblages in one observation were on the order of 30 Jlm sec· l (Ammerman
and Azam, 1984). Cells may also become clustered as a result of turbulence and sheer,
independent of biological mechanisms (Mitchell et at., 1990). So, bacteria are quite close to the
particulate loci of organic matter, and it would be surprising indeed if they did not interact with
them. Also, the intervening space contains colloids and polymers which may, in part, be
sloughing off from the surfaces of phytoplankton and detritus (below), and with which bacteria
may also interact along the way.