49
products is strong evidence for a tight metabolic coupling between
UDOM production and utilization. Although we have not tested it, we
predict that bacteria also take up the organic moiety of the OP compound hydrolyzed in preference to the same molecular species in the
bulk-phase.
Non-random Distribution of Bacterioplankton
We have so far discussed how marine bacteria might interact
metabolically with DOM components diffusing up to the cell surface.
It would seem that bacteria could enhance nutrient uptake by being in
close vicinity of a source of DOM. We have recently proposed that
bacteria might cluster in the vicinity of sources of sustained UDOM
production (e.g. exuding algal cells or detritus undergoing hydrolysis)
(cluster hypothesis; Azam and Ammerman, 1984). This spatial coupling
would increase the encounter frequency between bacteria and the DOM
molecules emanating from the source. We think that the clustering
bacteria, due to the existence of high Km, high V max uptake systems,
could remove a significant part of the new DOM before it diffuses into
the bulk-phase. Such clustering could increase the degree of coupling
between DOM production and its utilization by bacterioplankton.
Chemical Cues in Bacterial Algal Interactions
Healthy phytoplankton cells generally do not have any attached
bacteria. Bacteria readily attach to dead algae and detritus and are
believed to be important in POM decomposition.
It is not clear why
marine bacteria do not attack healthy phytoplankton, but the general
belief is that algae excrete repellents to keep bacteria away
(Sieburth, 1968). Yet, algal exudation is apparently one of the major
sources of UDOM for bacteria (Hagstrom et al., 1979; Williams, 1981;
Wiebe and Smith, 1977). Bacteria are attracted by one or more
components of algal exudates (Bell and Mitchell, 1972). Smith and
Higgens (1978) have suggested that metabolic feedback between bacteria
and algae might exist. However, the identity of metabolic effectors
(positive or negative) exchanged between bacteria and algae remains an
exciting research problem.
It is interesting in this context that cAMP, a Ubiquitous
metabolic regulator, was found to be excreted by freshwater algae
(Franko and Wetzel, 1980, 1981). Ammerman and Azam (1981) found
dissolved cAMP in seawater samples in concentration range of 1 to 30 pM,
products is strong evidence for a tight metabolic coupling between
UDOM production and utilization. Although we have not tested it, we
predict that bacteria also take up the organic moiety of the OP compound hydrolyzed in preference to the same molecular species in the
bulk-phase.
Non-random Distribution of Bacterioplankton
We have so far discussed how marine bacteria might interact
metabolically with DOM components diffusing up to the cell surface.
It would seem that bacteria could enhance nutrient uptake by being in
close vicinity of a source of DOM. We have recently proposed that
bacteria might cluster in the vicinity of sources of sustained UDOM
production (e.g. exuding algal cells or detritus undergoing hydrolysis)
(cluster hypothesis; Azam and Ammerman, 1984). This spatial coupling
would increase the encounter frequency between bacteria and the DOM
molecules emanating from the source. We think that the clustering
bacteria, due to the existence of high Km, high V max uptake systems,
could remove a significant part of the new DOM before it diffuses into
the bulk-phase. Such clustering could increase the degree of coupling
between DOM production and its utilization by bacterioplankton.
Chemical Cues in Bacterial Algal Interactions
Healthy phytoplankton cells generally do not have any attached
bacteria. Bacteria readily attach to dead algae and detritus and are
believed to be important in POM decomposition.
It is not clear why
marine bacteria do not attack healthy phytoplankton, but the general
belief is that algae excrete repellents to keep bacteria away
(Sieburth, 1968). Yet, algal exudation is apparently one of the major
sources of UDOM for bacteria (Hagstrom et al., 1979; Williams, 1981;
Wiebe and Smith, 1977). Bacteria are attracted by one or more
components of algal exudates (Bell and Mitchell, 1972). Smith and
Higgens (1978) have suggested that metabolic feedback between bacteria
and algae might exist. However, the identity of metabolic effectors
(positive or negative) exchanged between bacteria and algae remains an
exciting research problem.
It is interesting in this context that cAMP, a Ubiquitous
metabolic regulator, was found to be excreted by freshwater algae
(Franko and Wetzel, 1980, 1981). Ammerman and Azam (1981) found
dissolved cAMP in seawater samples in concentration range of 1 to 30 pM,