Microbial Biology II Módulo: Protozoários

Lectures 5 & 6
Lecturer:
Prof. Helena Galvão
Microbial activity in marine sediments
Oxic Zone:
- Nitrification
- Sulphur
oxidation
- Aerobic
degradation of
organic matter
Interface:
- Denitrification
Anoxic Zone:
- Sulphate
reduction
- Anaerobic
degradação of org.
matter
- CH4 production
Growth of different bacterial species
in relation to pH and Eh (redox
potential)
Typical vertical profiles of chemical
variables in marine sediments and
overlying water (Hiddensee, Baltic
Sea)
Bacterial distribution and activity in marine sediments
O2 in overlying water diffuses into
sediment following seasonal variations in
concentration.
Seasonal variations in O2 uptake and
sulphate reduction rates depending
on water temperature.
N Cycle – Biochemical processes
Main biochemical processes in N cycle.
A, B.2 & D are exclusively mediated by
bacteria.
Main compounds, aerobic/anaerobic
processes and changes in oxidation states
(arrows).
Carbon cycle vs Nitrogen cycle
Main processos in Carbon cycle.
Dashed arrows: aerobic processes;
continuous arrows: anaerobic
processes.
Main processes in Nitrogen cycle.
N.B. Ammonification: aerobic/anaerobic
degradation of nitrogenous org. matter;
nitrate ammonification or dissimilatory
reduction under limiting NH3. Both
processes are performed by all
microorganisms.
Nitrogen cycle in Baltic Sea water column
Central Baltic Sea (Gotland Deep) with
max. depth of 220m exhibits permanent
bottom anoxic layer due to long
residence times (100s years) and
eutrophication.
Vertical profiles at C station in Gotland Deep. Vertical
variation of N compounds reveals ammonification zone (040m); nitrification zone (50-120m); thin denitrification layer at
chemocline/oxicline (120m); anoxic zone with sulphate
reducion (120-220m).
Sulphur cycle in water and sediments
Aquatic S cycle is biochemically less
complex than N cycle with fewer
processes and S compounds. Main
processes: sulphurication or sulphur
oxidation and desulphurication or
sulphate reduction.
S cycle in marine sediments.
N.B. Permanent loos from cycle with
precipitation FeS2 (pyrite) insolubele in
seawater.
Aquatic Phosphorus Cycle
Main cell pools of phosphate
compounds: PO43-, ADP/ATP &
ADN/ARN
P cycle does not involve biochemical processes
with all P compounds maintaining same
oxidation state. In this ecological cycle,
phosphate is transfered between reservoirs
(inorganic
organic; dissolved particulate)
Significance of Redfield ratios in marine biogeochemistry
 In 1934, Alfred Redfield (1890-1983) wrote a now classic paper in which he
proposed that the N:P ratio of plankton (16:1) causes the ocean to have a
remarkably similar ratio of dissolved NO3(-) and PO4(3-). This hypothesis
suggested that, devoid of life, the chemical composition of the oceans would be
markedly different. The concept of Redfield ratios has been fundamental to our
understanding of the biogeochemistry of the oceans ever since.
 In the oceans most of the biomass comprises small drifting organisms (plankton)
that are rich in nitrogen. These organisms are essentially functionally similar
ensembles of metabolites, often encased in a shell formed from the most readily
available elements. Much plankton is consumed by other plankton with similar
chemical compositions. The result is that on average, the nitrogen:phosphorus
(N:P) ratios of plankton in the oceans are remarkably similar throughout the
world, averaging approximately 16:1 by atoms.
 The fact that the NO3-:PO43- ratio in the interior of all major ocean basins is
remarkably similar to the N:P ratio of plankton is due to the residence times of
these two elements in the ocean (roughly 104 years), relative to the ocean's
circulation time (roughly 103 years). As the residence times exceed the mixing
times by an order of magnitude, it should not be surprising that the NO3-:PO43ratios in the ocean interior are remarkably constant.
Nitrate vs phosphate in samples from the Atlantic
Redfield ratio of
15N:1P is
consistently found
in DIN
concentration in
samples
throughout the
Atlantic Ocean.
Redfield ratios in POM
Ratios in
surface
POM
Nitrogen Fixation in the Oceans
Oceanic filamentous cyanobacteria
such as Trichodesmium fix nitrogen
without heterocyts either at night or
by switching off photosynthesis
periodically to reduce intracellular O2
which inhibits nitrogenase activity.
Marine Nitrogen Fixation
N fixation in marine waters is
mainly carried out by
cyanobacteria both
filamentous and unicellular;
however, in estuarine
sediments other bacteria fix
nitrogen such as as
Azotobacter and Vibrio spp.
Nitrogen limitation in the oceans
Nitrate is generally limiting or nondetectable in surface mixed layer due
to uptake by both phytoplankton and
bacterioplankton
Maximum ammonium oxidation (1st step in nitrification)
occurs in surface mixed layer (ca. 100m) whereas maximum
nitrite oxidation occurs in deeper waters (ca. 400m) implying
a vertical zonation of two different types of nitrifying bacteria
performing either nitritation or nitratation.
Impact of global changes on N cycle
In interglacial periods,
microbial loop is
stimulated in warmer
waters reducing O2 and
nitrate, thus resulting in
higher denitrification
relative to DIN (Diss.
Inorg. Nitrogen) inputs.
In glacial periods, colder
waters have low
microbial activity
increasing O2 and
nitrate, thus yielding
lower denitrification
relative to DIN inputs.