University of Groningen
Nitrogen-fixing cyanobacteria in a marine microbial mat
Stal, Lucas Johannes
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2008
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Stal, L. J. (2008). Nitrogen-fixing cyanobacteria in a marine microbial mat s.n.
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SUMMARY
The nitrogen
cell
cycle
naÈeria1;
nLtrogen.
flnally
oiÈrogen
acts
loeses.
these
In
llr0iÈ6
nany
avallabiltty
of
and especÍaLly
zones that
The ain
The lncertidal
flat
that
photosynthesls
finally
scipulates
organlc
natter
procesa
ao aerobÍc
but
comes anaeroblc.
rílth
bacterla.
reducing
sulfate
to sulfide.
bacÈeria,
nanely
the purple
bacÈerl-a ls
Vertlcally
characÈerlzed
stratified
sulfate-reduclng
Melluro lsland.
resultant
of
of
oxygen
These bacteria
and netebol-Íc
large
leathery
areas
of
were
maÈs. Cyano-
oleroorganlsms.
bacterla.
the
slnple
The layer
out
oxldlzed
of
be-
naÍnly
by
conpounds by
by anoxyphoto-
Lhe sulfaËe-reducing
purple
gradlenÈs
activltÍes
Ís
lhls
envl-ronnenÈ
organlc
of
The dead
First,
duê to preclplÈated
well-developed
The steep physico-chemlcal
growth
on the island
island
1s eventually
color,
characterlze
whlch
condltlons.
sÈep Ls carrled
oxidlze
bacterí.a.
by a black
of
Ln an
cyanobacterla
depletlon
populatl-ons of cyanobacÈeria,
bacteria
the
the
tough,
groups
other
The sulflde
of
1s sltuated
by chenoorganotrophic
sulfur
the role
Í0aln lnput of organie rnacerial whlch
the
increasing
nltrogen
SeawaÈer and
pure quarz are very
under aeroblc
The fl-na1 ninerallzation
sulfate-reduclng
theÈ counÈer-
of cyanobacteria
adapEatlons
whLch forn
presentB
nlneralLzed
nolecular
bound nitrogen.
conbl.ned
of almost
I'esÈ beach of
Ehe presence of
is
lnto
production.
of populatlons
nitrogen
the process
of
of
of
is
process
e source
prloary
nas LnvestlgaÈed
Sea. On the
covered by benÈhic cyanobacterla,
bacterial
lose
the only
consist
actÍvity
nlÈrogenase
North
southern
cycle
of Èhls thesl-s na8 Lo study
zone and the physiological
of
Al-l eukaryoÈes
are able to grow w1Èh
biological
bound nitrogen
of
nicro-
the synthesis
Denltrlfication
ls
ln the developnent
them Èo maintaÍn
Mellun,
fixaÈLon.
by prokaryotes
the
niÈrogen.
fixatlon
lntertidaL
enable
fixaÈlon
of incertidal
poor in conbined
the
presenÈs a continuous
of organisns
sandy sedloents
ln
the conversion
eÍwironments
the gronth
nltrogen
ln
denitrlflcatlon
Blologlcal
reactions
for
are dependent on a source of
nuober of bacteria
and nltrogen
results
Thus,
organlsms
a linited
by prokaryotic
driven
eleoents
I47. of. dry rrelght.
approxinaÈely
The cruclal
are denitrLficaÈion
which
essentially
of the prokaryotic
combined niÈrogen.0n1y
nitrogen.
for
1È accounts
and Ehe oajority
molecular
naÈure ia
in
is one of the nosÈ iDportant
Nltrogen
organisns.
sulfur
nlcrobial
anorphous FeS.
bacÈeria
oats
and
on the
Ín these maÈs are the
Ëhe conÈributing
organ-
r59
lsms.
Although,
diverse,
lt
at flrst
stghE,
was found that
the cyanobàcterial
only
two specles
comnunl!y
parEicular
were of
filamenÈous OseíLLator,ía sp. \Ías Lhe organlsm that
sedioenL.
In a later
of nat
stage
became a dominant organlso.
sp., however,
The latter
1s present
usually
developmer't
seemed rather
inltial1y
was Lhe real
with
The
maÈs, are
coupeÈed due to extrenely
Eat builder.
)ecdLLator"La
and sometLmes may even become doninant
nltrogenase
the
layer
much no heterocyst-fornlng
samples of the nat.
actlvlÈy
ln
Èhe nicroblal
of cyanobacÈeria.
could
Nltrogenase,
be detected
Thls
in
the
maÈ shoríed a
was astonishLng
by oicroscoplc
the enzyme responsible
for
lnas-
exaninaÈlon of
nltrogen
fixation,
1s exÈremely sensitive
to oxygen and therefore aerobic organisms have to
possess oxygen protection
nechanisms. Certain species of the aeroblc and
oxygenlc phototrophic
cyanobacterla
forrn speciallzed cells, the heterocyst.
The heterocysÈ
site
does not
of nitrogen
nlcrobial
nat
evolvê
flxaÈlon.
oxygen by photosynthesÍs
showed a close association
Idas astonishlng
and thls
The neasuremenÈs of nltrogenase
with
the layer
inasmuch no heterocyst-forning
cell
activiÈy
doninated by )seíLlator"La sp. showed a specific
(expressed as rng chlorophyll)
which was considerably
than 1n esÈabllshed nats.
By isolating
could
organlsm
be shown that
nitrogen
lrhich
ion
thls
possessed high
and Èhat it
Ehe cyanobacterla
against
overcone
oxygen lnactivaÈion
the
in Èhe
This
could be detected
Young mat systems,
genase actlviÈy
ts
of cyanobacteria.
cyanobacteria
nltrohlgher
ehthonopLastee
the problens
related
in
the
to nltrogenase
field
and in
the labora-
0scilLator'ía
niErogen f ixation predonin
offered the organisxo the Po
oxygenic
fron
Photosynthesis
nitrogenase aPPe
periods,
pertod.
dark
genase actlvity
gradient
occurred
rnicro-electrodes,
oxygen was maxlnal
in
Èhe sedíment, it was shovn that maxlmum nitroin a depth of 2 - 3 nrn. Oxygen-proflles,
measured by
have shown that
in the upper l-nn
ln
the llght
the concenlration
of the sediment,
of
whereas below 1.5 nm
depÈh vlrcually
cultures
grown under continl
ïn
a htgh activiÈy
morning,
active
anaetobic
at sunrlse.
oxygenic
In summary,
photosynthesis.
in
Èhese observations
the observed nitrogenase
160
a period
phoÈosysten II
genic
ls
were taken
as evidence
sp. was responslble
Many other
was striking
nitrogen
cyanobacteria
thaÈ also
several
fixation.
ÈhaÈ the nonfor
Èhe bulk
were isolaÈed
heterocystous
of
fron
cyano-
is
los
synthesized
nitrogen ls:
if sufficlenE
gênase activiÈy
disaPPears.
ls
sêparatlo
nechanisn
an inportant
cannot
alone
mechanism
cause niÈrogenase
exP
must alsc
mechanlsms rnay be conside
in
activitY
occurs
the enzyne apl
I
fixatlon.
neE nitrogen
of
synthesls
level
perlod,
night
in
and also
probably
30 h showed
is sti11 anaerobic in Èhe
presumably does not supporE
The presence of lord light
intensity
and
)seíLlatoría
activiÈy.
It
of
lntensity
the sedlment appeared to stinulate
cyanobactetium
saoe environment.
during
The sedlmenE probably
whereas the 1orí lighÈ
condlcions
heterocystous
the
the acce
phycobillprotein
of
cular
very
absence of
the
phycobillproÈeins,
oxygenic photosynthesls bu! presuoably a11ows non-cyclic
electron
transporÈ
through photosystern I. Measurenents of oxygen concentration
have also shown
that during the dark period the sedinent turns anaerobic up to the mat sur-
early
and oxygen
NlÈrogen fixation
cesses.
a 1i1
Therefore,
activity.
nitrogenase
reducÊion measured repetitively
f
nitrogen
llght'
no oxygen could be detecÈêd. Moreover, only light
of long
wavelength penetrated Èhe cyanobacterial
maE relaÈively
wel1. The llght
ÈhaÈ
reaches the lolrer layers of Èhe cyanobacterial
mat, certainly
does not support
face. Àcetylene
a
Transferrlng
tinuous
The Èenporal
In a vertlcal
cont
crowing
nlÈrogenase
were studied
of nitrogen
organism will
Èhat thÍs
ni
fixed
also
induction
EOry.
uslng
possessed Èhe cap
organlsms
nitrogenase
by
protec!-
fj
and fllanenÈou
unicellular
degree
The oechanlsns
obscure. AP
still
0ecilLatonía
Bp. 1n pure culÈure, it
grer{ vell
ln the absence of conblned
acÈlvity.
isolated
the
that
The measurements of
assoclatlon
The reasons why tl
lnterest.
M. ehthonoplaatea-mat.
close
were
nitrogen.
colonlzed
Mícr.ocoLeue ehthonoplaetes
af
bacteria
may contrlbute
Usual1y,
to
cYanobacter:
endogenous carbon
anaerobic
Protect
the llg
durlng
reserves
the night.
naEs must possess rnechanis
least for the purPose of na
cyanobacter Ia, 0eciLLator
dark
anaeroblc
netabolisn
ln
carbon reserves
condltlons
Èhis organlsn
inÈo lactat
bacteria
were
rl coEmunity seened rather
of parLÍ.cular LnÈerest. The
nl-Erogen.
The reasons
.at lnltial1y
colonlzed Èhe
'í e n o
c oLeue ehth onopLae t e s
conpeÈed due Èo extrenely
rl mac bulldet.
)eeiLlatonía
even become domlnanÈ tn
Èhe roicrobLal
the
nat
showed a
Thls was astonlshing
inas' roicroscopic exanlnatlon
of
rlble
for
aerobic
ni-Èrogen fLxatton,
organisos
rpecles of
have to
the aeroblc and
llzed cells, the heÈerocyst.
:hesis and this ce1l ts the
ltrogenase acÈlvity in the
nats,
isolaÈed
are sElll
possessed the
organlsns
chthonoplastee
that
lnduction
that
this
of nltrogenase
organlsn
0seiLLatoría
oxygenic
phoÈosynthesis.
fron
perlods,
dark
period.
niÈrogen
are outoÈher
and sone of Èhese
anaerobicalLy.
However,
conÈrlbute
taking
Èo overall
M.
inÈo account
it
was doubted
nlÈrogen
hlgher
actlvity.
nia sp. Ln pure culture,
1t
r the absence of conbl-ned
degree
fixaÈion.
ctlviÈy.
The nechanisns by
ted Èo nitrogenase proÈect-
nLtrogenase
photosysÈen II
ls
llght
the acces8ory
is
synthesized
The tenporal
separatlon
mechanisn
.lghÈ the concentratlon
cause nl-trogenase must also
an loportanÈ
alone
nechanisn
cannot
the
of
nÍtrogen
of
cyanobacterlun
photosysten
of
againsL
the
are resynthesized.
in
the
When a cerÈain
oxyThen,
resumes and nltro-
and nitrogen
these
fixaÈion
Horrever,
cyanobacteria.
fixatlon
be protected
pro-
degrades
oxygen has stopped,
of
photosynEhesis
nitrogen
II.
phoÈosynthesls
Ln non-heÈerocystous
explaln
con-
nitrogenase
Èhe activlty
phycobillproÈeins
oxygenic
to
seem Èo be lncompatible
the
Ls reached,
oxygenlc
cycle,
11ghÈ. Moreover,
an absoluÈe prerequislte.
1s not
As soon as the evolutlon
and the
maxinum nttrorygen-profiles,
neasured by
in
shorÈ dark
the onset of the
showed a discontlnuous
plgments
ls fl-xed,
nitrogen
lf sufficlenE
genase actlvi!y
disappears.
ls
also
cycle
degradatlon
lost.
using
beforê
grown under a light-dark
conÈlnued also
conbined
phycoblliprotein
of
ln the light
and oxygenic photosynthesls
absence of
the
phycobillproteins,
genlc
fixation
a 1lghÈ-dark
Therefore,
In
iÈ was observed Ehat,
Ilowever,
grown under continuous
cultures
h was considerably
of
were lsolated
showed a 1ag of at leasÈ 8 h,
a culture,
Transferring
tLnuous light,
cesses.
r shown that
conblned
Èhe Mellun
Several
conditLons.
synÈhesize nÍtrogenase
appeared already
nltrogenase
Nitrogen fixaÈion
labora-
of
in
sp. in the laboratory
under light-dark
cycles,
predonlnantly
occurred in the dark. The llght-dark
nitrogen flxatlon
cycle
to separaÈe nitrogen fixaÈion teoporally
offered the organisno the posslbillÈy
nltro-
the
deprived
no importance
anaerobically.
consÍderably
Growing
sp. showed a speclflc
and in
will
to
nitrogen
of
environmental
cyanobacterla
capaclty
al-so fixed
on nedia
are
the heEerocysÈous cyanobacteria
fluctuatlng
and filarnentous
unlcellular
enrichnent
organlsns
obscure. Apparently,
Layer of cyanobacteria.
This
robacÈerla could be detecÈed
re fleld
afÈer
why these
Èhis
cyanobacÈeria
atrnospheric
oxygen.
be-
Several
rênÈ, whereas below 1.5 nn
eover, only llght
of long
nechanisos
nay be consLdered. There 1s no doubt ÈhaÈ a conÈinuous loss
niÈrogenase
activity
lvely
synÈhesis
wel1.
Thê lighr
rhar
certaÍnly
:yclic
does not support
electron transporE
centration
have also shor.rn
rerobic up Èo the oat surLng a perlod of 30 h showed
ls sti1l
anaeroblc
tn the
esunably does not support
1ow light
lntensiÈy
and
rf
inulate
nltrogen
rs evidenee
esponslble
acterla
that
fixation.
Èhe non-
for
Ehe bulk of
were isolaÈed fron
rveral heterocystous
cyano-
ln
of
the enzyme apparenÈly
neL nlÈrogen
cular
level
occurs under aerobic
fixatl-on.
condiÈlons.
counÈeracts
Additionally,
Honever,
losses
a switch-off
mlght protecÈ Èhe enzyme during
of
a high
actLvlty,
nechanlsn
oxygen stress.
of
raÈe of
resulÈlng
on the
nole-
Durlng the dark
when photosynÈhetlc activity
stops, respiration
and also in the light
probabJ-y nay conÈrlbute to keep the intracellular
oxygen concenÈration low.
perlod,
Usua11y, cyanobacteria survlve
(glycogen).
endogenous carbon reserves
anaerobl.c durlng
the nighf.
mats must possess oechanisns
least
for
0scillatoría
dark anaerobic
conditlons.
metaboll.sn
1n this
carbon reaervea
into
organlsn
laccale
Microbial
Therefore,
by respiraÈion
of
maEs on Melluro island
Èhe cyanobacÈeria
to generate
Èhe purpose of maintenance.
cyanobacterLar
dark perlods
Ehat occur
energy anaerobically
FurÈhermore,
and in
sp. was shown Èo be able
in
ln
Èhese
the dark,
conLrasÈ nlth
to flx
Èheir
become
nltrogen
aÈ
oÈher
under
This also indicated Èhat anaerobic dark energy
1s possible. OecíLlatoría
sp. fermented endogenous
and elhanol
in
a heterofermentatí.ve
pathway.
In
Èhe presence of elemenÈal sulfur,
was reduced to
sulfur
sulfide.
reductlon
did not occur.
sulfur
present, lactaÈe fernenÈatlon
presence
to
of
elemenÈal
sulfur.
reduction
of
Cells
contaLning
fernenÈatLon
is
presently
onl-y degraded glycogen
elenenÈal
sulfur,
was repressed
produclng
subsÈrate
also
nltrogenase
occurred
The repression
of
the dark
thê
noÈ understood.
anaerobically
sulfide.
Except
in
for
nutrlent
t62
flexlblllty
envi-ronment.
nitrogen
under aeroblc
allor.red )scíLLator'ia
sp.
conditions
to
colonlze
ln
)eciLlator'í.a
Èhe Mellun sÈrains Èested possessed fermenÈative pathways.
but noÈ all - strains were able Èo reduce elenenÈal sulfur.
The capaclÈy to fix
was
1n the
reduced aceÈy1ene
was observed.
none of
neÈabollc
and
nltrogenase,
contained
Unless a nitrogenase-reduclble
by nltrogenase
M, ehthonopLastes
presence
fernentaÈion
under such conditlons
eÈhylene and then no lactate
sulfur
lactate
However, Íthen the cells
and its
Several
sp.
-
astonishlng
an exÈremely
low