MECHANISMS OF ORGANIC MATTER UTILIZATION BY
MARINE BACTERIOPLANKTON
F. AZAM and J.W.AMMERMAN
Institute of Marine Resources, Scripps Institution
of Oceanography, La Jolla, California 92093, USA.
Recent work indicates that bacteria in the sea may consume 10-50%
of the primary production (Hagstrom et al., 1979; Fuhrman and Azam,
1980, 1982; Williams, 1981), and the resulting bacterial secondary
production is presumably channelled into a dynamic microbial foodweb
(Azam et al., 1983). These observations have generated much interest
in the coupling between the production of organic matter and its
utilization by heterotrophic bacterioplankton, since this coupling may
determine how the primary production is partitioned between the
classical grazing food chain and the emergent microheterotrophic
foodweb.
The finding that bacterioplankton is a major route for the flow of
matter and energy in the marine foodweb is in apparent contradiction
with the conventional wisdom that bacterial nutrients are too dilute
in seawater to support rapid bacterial growth.
In this paper, we will
argue that marine heterotrophic bacteria utilize organic matter in
close metabolic and spatial coupling with the sources of organic
matter, and this explains why they are so effective in consuming
organics from seawater.
Sources and Modes of Organic Matter Production
Bacterial nutrients in seawater are chemically and physically
diverse. The dissolved organic matter (DOM) contains, at very low
concentrations, many solutes which are directly utilizable by marine
bacteria (e.g. sugars, amino acids, organic acids).
Some other
solutes (e.g. proteins, polysaccharides, organophosphorus compounds)
are not transported into bacteria; they are generally hydrolyzed
extracellularly and the hydrolysis products transported across the
palsmalernrna of the bacterial cells. Likewise, particulate organic
matter (POM) must be hydrolyzed to make it accessible to membrane
MARINE BACTERIOPLANKTON
F. AZAM and J.W.AMMERMAN
Institute of Marine Resources, Scripps Institution
of Oceanography, La Jolla, California 92093, USA.
Recent work indicates that bacteria in the sea may consume 10-50%
of the primary production (Hagstrom et al., 1979; Fuhrman and Azam,
1980, 1982; Williams, 1981), and the resulting bacterial secondary
production is presumably channelled into a dynamic microbial foodweb
(Azam et al., 1983). These observations have generated much interest
in the coupling between the production of organic matter and its
utilization by heterotrophic bacterioplankton, since this coupling may
determine how the primary production is partitioned between the
classical grazing food chain and the emergent microheterotrophic
foodweb.
The finding that bacterioplankton is a major route for the flow of
matter and energy in the marine foodweb is in apparent contradiction
with the conventional wisdom that bacterial nutrients are too dilute
in seawater to support rapid bacterial growth.
In this paper, we will
argue that marine heterotrophic bacteria utilize organic matter in
close metabolic and spatial coupling with the sources of organic
matter, and this explains why they are so effective in consuming
organics from seawater.
Sources and Modes of Organic Matter Production
Bacterial nutrients in seawater are chemically and physically
diverse. The dissolved organic matter (DOM) contains, at very low
concentrations, many solutes which are directly utilizable by marine
bacteria (e.g. sugars, amino acids, organic acids).
Some other
solutes (e.g. proteins, polysaccharides, organophosphorus compounds)
are not transported into bacteria; they are generally hydrolyzed
extracellularly and the hydrolysis products transported across the
palsmalernrna of the bacterial cells. Likewise, particulate organic
matter (POM) must be hydrolyzed to make it accessible to membrane