Evolution, Diversity and Molecular Ecology

1
(No Transcript)
2
(No Transcript)
3
(No Transcript)
4
(No Transcript)
5
Evolution, Diversity and Molecular Ecology of
Marine Prokaryotes 1.The most abundant
bacterioplankton have never been cultured. 2.The
major marine prokaryotic groups appear to have
cosmopolitan distributions. 3.A relatively small
number of uncultured marine bacterial clades (9)
account for 80 of marine Bacteria 16S rRNA gene
clones recovered from seawater. 4.Marine Archaea
are abundant, and almost invariably fall within
two groups. 5.There is much genetic diversity
within the major prokaryotic plankton groups. It
is not yet known how much ecological
specialization occurs among the species that make
up groups, but in some cases members of these
groups are distributed differently with
depth. 6.Particle-associated and
freely-suspended marine prokaryotes are
different. 7.Stratification of bacterioplankton
populations is typical of the ocean surface
layer.
6
(No Transcript)
7
Bacterial Production and Biomass in the
Oceans 1.Bacterial standing stocks in the
euphotic zone average about 0.5 - 2 gC m-2 across
a range of oceanic systems. The ratio of
bacterial to phytoplankton stocks varies widely,
from less than 0.1 in polar coastal seas to over
2.0 in the oligotrophic gyres. 2.Bacterial
production is maintained in a remarkably constant
ratio to primary production, averaging about 0.15
- 0.2 across oligotrophic and oceanic HNLC and
upwelling and blooming systems. Bacterial
production is generally much lower during polar
coastal blooms, but can be high following the
peak phase of blooms in temperate and sub polar
regimes. 3.Bacterial stocks seem to be limited
principally by resource limitation in
lower-productivity systems, but removal processes
are more intense in coastal and estuarine
systems, suppressing integrated standing stocks
to below oceanic levels. 4. Better recognition,
detection and understanding of inactive cells are
needed to specify rates and mechanisms of
bacterial growth.
8
(No Transcript)
9
Production Mechanisms of Dissolved Organic
Matter 1. In cultures, exponentially growing
phytoplankton release on average 5 of total
primary production as DOC. This value tends to be
higher when algal cells have been exposed to
sub-optimum conditions. In natural environments,
the extracellular release of DOC typically
accounts for ca. 10 of primary production, which
is not sufficient to fulfill bacterial carbon
demand. 2. Protozoan grazers can release 20-30
of ingested prey organic carbon as DOC. The
corresponding values for metazoan zooplankton are
10-20. Egestion of unassimilated prey material
appears to be a major mechanism of DOM release by
grazers. 3. Viral infection of host cells
(phytoplankton and bacteria) may result in
substantial release of DOM. Beca use viruses can
be a significant cause of mortality for bacteria
and phytoplankton, the contribution of viruses to
DOM production in seawater is potentially
large. 4. A flood flow model for oligotrophic
open oceans suggests that grazers, particularly
protozoa, are the major contributor to DOM
production. This type of oceanic ecosystem is
characterized by intensive recycling of organic
carbon through DOM-microbial food chains. 5.
Geochemical studies have suggested that a
substantial portion of high molecular weight
refractory DOM in oceanic water is derived from
bacteria. The release into seawater of structural
components of bacterial cells during protozoan
grazing and viral infection could be a key
mechanism that controls refractory DOM cycles in
the oceans.
10
DOM- Dissolved organic matter or DOC (dissolved
organic carbon)   Two pools of DOM   1. Labile-
easily used by bacteria, rapid turnover rates
Includes sugars and some complex carbohydrates,
amino acids and proteins, nucleic acids, organic
acids such as acetate. Low levels (nanomolar,
hard to measure) because it is snapped up almost
as quickly as it is produced by
phytoplankton.   2. Refractory- gt90 of total
DOM, Old (1000s of years), already picked over
for anything usable- largely humics and fulvic
acids, but poorly characterized.   Bacteria
depend on labile DOM- this is the major link
between primary and secondary producers.   Labile
DOM can be produced by -Phytoplankton "leakage",
especially from nutrient-limited cells.
(Exudation) -Fecal pellets and excretion by
metazoan or protozoan grazers -"Sloppy feeding"
by grazers -Viral lysis of bacterial or
phytoplankton cells -Bacterial exoenzymes
11
(No Transcript)
12
Heterotrophic Bacteria and the Dynamics of
Dissolved Organic Material 1. Several studies
indicate that 50 of primary production passes
through DOM prior to decomposition, there are
careful contemporary studies that give rise to
values as low as 2 and as high as 130. In part
this is a reflection of the insufficient data
base on heterotrophic processes in the global
ocean. 2. Most marine microbiologists would be
inclined to use either thymidine or leucine
incorporation to measure bacterial production,
but due to uncertainties over conversion factors,
presently bacterial carbon use is probably most
accurately estimated from respiration
measurements. 3.A major factor limiting our
understanding of the exact role of bacteria in
ocean carbon flux is the uncertainty over the
carbon growth yield of oceanic bacteria. The
general downward revision of the value for
bacterial growth yield in recent years swings the
balance towards bacteria as sink of organic
material rather than a link. 4.We are going
through a revision of our expectation of the
factors that limit the growth rate of
heterotrophic bacteria. Simple carbon limitation
no longer appears to be the exclusive
mechanism. 5. The scale of photochemical
reactions is significant in the overall turnover
of DOC. Rates of photochemical production of
carbon dioxide from DOC can be comparable to
rates of microbial respiration. All the signs are
that chemical (both dark and photochemical) and
microbiological transformations of dissolved
material cannot be considered as isolated routes
13
(No Transcript)
14
Bacterial Energetics and Growth
Efficiency 1.Bacterial growth efficiencies in
natural marine systems are generally low (lt0.3).
The low BGE are the combined result of the nature
and supply of organic and inorganic substrates,
and most likely also of the high energetic cost
associated with life in very oligotrophic
systems. There is a positive relationship between
growth efficiency and primary production. 2.The
energetic costs of the production of exoenzymes,
active solute transport, and the excretion of a
variety of polymers have not been investigated in
natural bacterioplankton. In particular, the
concept of maintenance energy requirements has
never been explicitly investigated for
bacterioplankton. 3.Bacterial respiration is
much less variable than bacterial production
across marine systems, and it is clear that BGE
is driven by changes in bacterial production
rather than in bacterial respiration. Bacterial
production alone is not a good index of either
organic carbon consumption or availability, and
grossly underestimates the carbon flow through
bacterioplankton. 4.There are relatively few
direct estimates of bacterioplankton respiration,
and we are barely beginning to understand the
regulation of microbial respiration, although
this is possibly the largest single component of
organic carbon flow in most marine
systems. 5.One fundamental unanswered question
is whether the low BGE measured in marine systems
is the result of genotypic or phenotypic
adaptation of the bacterial assemblage.
15
(No Transcript)