Indian Journal of Geo-Marine Sciences
Vol. 41(5), October 2012, pp. 405-411
Distribution of Aerobic and Anaerobic Bacteria along the Intertidal Zones of
Sunderban Mangrove Ecosystems, NE Coast of Bay of Bengal, India
S.Das1, M.De2, T.K.De1*, R. Ray1, T.K. Jana1 P. K. Ghosh3 & T.K.Maiti3
1
Department of Marine Science, Calcutta University, 35, B.C. Road, Kolkatta-700 019, India
2
Manicktala Siksha Bhavan, 304/B/1 Bagmari Road, Kolkata-700 054, India
3
Microbiology Laboratory, Department of Botany, Burdwan University, Burdwan-713 104, India
*
[E:mail: [email protected]; [email protected]]
Received 11 March 2011; revised 16 November 2011
Population of aerobic and anaerobic bacteria along the different tidal zones of Sundarban Mangrove forest sediment
was studied to determine their distribution with the availability of different nutrients and other physicochemical parameters.
Lower littoral zone (LLZ) along the shore which remains inundated by sea water showed more population of anaerobic
bacteria (212 x 104 CFUg-1) than that of mid littoral zone(MLZ) (102 x 104 CFUg-1) and upper littoral zone(ULZ)
(60 x 104 CFUg-1). Population of aerobic bacteria was found to be maximum in ULZ (57 x 104 CFUg-1) compared to MLZ
(46 x 104 CFUg-1) and LLZ (14 x 104 CFUg-1). Population of methanogens increased with rise of sea level which in turn
emitted more methane than CO2. A stable dynamic equilibrium for growth rate of aerobic and anaerobic bacteria observed in
ULZ and is ecologically more consistent than LLZ particularly with respect to methane emission from sediment. Anaerobic
bacteria are relatively more tolerant to variable salinity, pH and other physicochemical factors than the aerobic bacteria.
[Keywords: Aerobic, Anaerobic, Bacteria, Sediment, Population]
Introduction
Mangrove forests are usually considered to be high
productive areas that support highly developed
detritus-based food webs1. High primary productivity
of mangroves implies a high demand for nutrients
essential to plant growth and this demand appears to
be met by a highly efficient system of nutrient
trapping, uptake and recycling2,3. Organisms within
mangrove ecosystems, including microorganisms,
plants and animals, show complex interactions.
Microorganisms are intimately involved in
biogeochemical cycling and in many instances are the
only biological agents capable of regenerating forms
of the elements used by other organisms, particularly
plants4. Therefore, Mangrove provides a unique
ecological niche to different microbes which play
various roles in nutrient recycling as well as different
environmental activities5. The decomposition in this
forest involves microorganisms at various tropic
groups acting in a multi step process The first step is
an enzymatic hydrolysis of polymeric material to
soluble monomeric and oligomeric compounds6.
Under oxic conditions the soluble compounds are
directly mineralized to carbon dioxide and water
where as under anoxic conditions various
physiological groups are involved in degradation after
the initial depolymerisation. Fermentative bacteria
convert the products of hydrolysis to a variety of
products, mainly short chain fatty acids, carbon
dioxide and hydrogen. Further conversion through the
action of secondary fermenters, sulphate-reducers,
acetogens and methanogens produces the end
products CO2, CH4 and H2S, which may escape into
the atmosphere7. All three are important greenhouse
gases. The organisms within mangrove ecosystems,
including microorganisms, plants and animals, show
complex interactions. Microorganisms are intimately
involved in biogeochemical cycling and in many
instances are the only biological agents capable of
regenerating forms of the elements used by other
organisms, particularly plants. Earlier Thomas et al8
established an ecological relationship between aerobic
and anaerobic bacteria available in the coastal
sediment. There are two distinct zones in soil i.e.
aerobic zone (Soil Surface) and anaerobic zone
(below 30 cm from soil surface) were studied to
examine the growth of two above mentioned bacteria
type (Fig. 1). The range of depth of these two zones
varied with different geochemical parameters. In
anaerobic zone methane is produced from carbon
dioxide and H+ ion by several methanogenic bacteria
which are anaerobic in nature. Hydrogen sulfide gas is
406
INDIAN J. MAR. SCI., VOL. 41 NO. 5 OCTOBER 2012
also produced from this zone by anaerobic bacteria.
These reduced molecules when reach aerobic zone,
they get oxidized by aerobic bacteria present in this
zone. Methanogens have the ability to obtain energy by
oxidizing hydrogen or formate and utilizing the
electrons thus generated to reduce carbon dioxide with
the formation of methane gas9. When this methane
when reaches to aerobic zone it is utilized by aerobic
bacteria to form carbon dioxide; unutilized methane
comes out from the soil and contributes to the
atmospheric trace gas composition. Therefore more
consumption of methane in aerobic zone will result less
emission from sediments. Thus a significant interaction
between aerobic and anaerobic bacteria is necessary for
the ecologically consistent of the environment.
Present study consists of the comparison between
population of aerobic and anaerobic bacteria and their
interaction in the different tidal zones of Sunderban
mangrove forest along the coastal zone of North East
coast of Bay of Bengal, India. It also elucidated some
light on the sediment with relatively population of
anaerobic methanogenic bacteria and effect of changing
different physicochemical parameters on aerobic and
anaerobic bacterial population of the change of sea level.
Materials and Methods
Study area
Sunderban
Mangrove
forest
is
located
geographically in between 21º 31’ N and 22º 30’ N and
longitude 88º 10’ E and 89º 51’ E along the North East
coast of Bay of Bengal, India. This mangrove forest is
a part of the estuarine system of the River Ganges, NE
coast of Bay of Bengal (Fig. 2), which covers
9630 km2, out of which comprise of inter-tidal area,
covered with thick mangroves, is subdivided as forest
sub-ecosystem and 1781 km2 of water area as aquatic
sub-ecosystem. The tide in this estuarine complex is
semidiurnal in nature with spring tide to range between
4.27 m and 4.75 m and neap tide range between 1.83 m
and 2.83 m. It is a unique bioclimatic zone in Land
Fig 1 Gaseous exchange between soil sediment and atmosphere
Ocean boundaries of Bay of Bengal. In the southern part
of the island, the ground level is high while in the
northern areas the land is low and gets inundated during
highest high tide. Avicennia alba, Avicennia marina and
Avicennia officinalis are the dominant mangrove species,
Excoecaria agallocha and Heritiera fomes are thinly
distributed and Ceriops decandra is found scattered all
over the island. The deltaic soil of Sunderban Biosphere
Reserve comprises mainly saline alluvial soil consisting
of clay, silt, fine sand and coarse sand particles. It is
described as very deep, poorly drained, fine soils
occurring on lower to nearly lower level delta with loamy
surface, severe flooding and very strong salinity
(extensive extent) associated with very deep, very poorly
drained, fine loamy soil. Sediment samples were collected
monthly from three intertidal zones of Sunderban
mangrove ecosystem during February 2008 to January
2009. Replicate Soil samples were collected aseptically
by using a hand–held stainless steel corer sampler from
the top 30 (3.2 cm diameter, 30 cm long) from Upper
Littoral Zone (ULZ), Middle Littoral Zone (MLZ), and
Lower Littoral Zone (LLZ) and average values were
taken. Soil samples were brought back to the laboratory in
iced condition in sterilized container.
Quantification of aerobic and anaerobic bacteria
Samples (about 10 g) from different tidal zone of
were homogenized with sterilized phosphate buffer
solution. Serial dilutions up to 10-4 were made and
inoculation was done with 0.1 mL. Quantification of
bacteria from mangrove sediments was carried out by
spread plate method Bacteria present in sediment were
cultured in Marine Agar 2216 Medium after isolation by
phosphate buffer solution10. In medium for anaerobic
Fig.2 Map showing the location of study area
DAS et al.: DISTRIBUTION OF AEROBIC AND ANAEROBIC BACTERIA IN SUNDERBAN MANGROVE ECOSYSTEMS
Bacteria, sodium sulfide was added as reducing agent. It
was incubated in anaerobic environment in Gaspak
anaerobic jar for cultivation of anaerobic bacteria11.
After same incubation period Colony Forming Unit
(CFU) of aerobic and anaerobic bacteria present in soil
surface sediment were counted to compare their growth
rate in different oxic and anoxic conditions Table 1.
Different kind of aerobic and anaerobic bacteria was
cultured in different selective medium with appropriate
condition for enumeration of bacterial population12.
Sediment quality measurement
Bio-available nitrate present in the sediment sample
was extracted with 2 M KCL solution and the extract
was used to estimation of nitrate spectrophotometrically.
The absorbance of the resulting pink solution was
measured photo-metrically at 543 nm against a reagent
blank13. For estimation of sulphate in the sediment
20 gm of it was dissolved in 100 mL distilled water.
After vigorous shaking for 1 hr the solution were filtered
through Millipore filter paper (0.45µm). The filtrate was
used
to
determine
sulphate
concentration
turbidometrically13. Soil was dissolved in distilled water
and chlorinity (Cl) of the water were determined by
Mohr-Knudsen titration method and standard seawater
of chlorinity 19.374 procured from the National Institute
of Oceanography Goa, was used for the standardization.
From the knowledge of chlorinity, salinity (S) was
calculated using the Knudsen relation: S (× 10-3) =
1.80655 × Cl (× 10-3). The soil pH was determined
following a water paste and determined by using micro
pH meter (Systronics, model No, 362). The organic
matter was determined by the modified Wakly–Black
method (oxidation with potassium dichromate in
sulphuric acid solution to obtain organic carbon).
Result and Discussion
Soil salinity varied in decreasing order from ULZ
to LLZ with highest and lowest values of 30.1±3.53
and 15.8±1.98 in ULZ and LLZ, respectively
(Table 1). Both Eh and pH values decrease from ULZ
to LLZ which indicates the oxic/anoxic nature of
sediment. Oxic conditions with relatively higher Eh
values in the sediment are favoarable for aerobic
bacteria but unfavourable for the anaerobic bacteria.
Sediment in the LLZ experience frequent tidal
inundation at a daily basis. Submergence may cause
more anoxicity relative to the sediment exposed to air.
Maximum and minimum concentrations of both
organic carbon and inorganic nitrogen were found in the
ULZ and LLZ sediments, respectively. Regular tidal
flushing which was more frequent in LLZ than the ULZ
could transfer more organic carbon and other nutrients
from the sediment from the former. An ecological balance
between the aerobic and anaerobic bacterial population
was recorded in the sediment collected from ULZ. On the
contrary anaerobic bacterial population in the LLZ
sediment was found almost 12 times higher than its
aerobic counterpart. After similar incubation period
Colony Forming Unit (CFU) of aerobic bacteria present
in soil surface sediment of ULZ was found more than that
of the aerobic bacteria present in surface soil sediment
collected from LLZ. This could indicate the persistence of
relatively greater anoxic condition at the lower littoral
zone than that of the upper littoral zone14. Fig. 3
represents the growth curve for both the mean anaerobic
Fig 3 Mean growth curve of aerobic and anaerobic bacteria in
three zones
Table 1 Physico-chemical parameters and CFUs of aerobic and anaerobic microbes in three intertidal zone
(Average values of 12 months are given with standard deviation)
Soil Parameters
Salinity (psu)
pH
Eh (mV)
Org Matter(%)
NO3-N-1 (µg g-1 dry soil)
SO4-S-2 (mg g-1 dry soil)
Mean CFU (Anaerobic)
Mean CFU (Aerobic)
407
ULZ
MLZ
LLZ
30.10±3.53
8.01±0.2
-94.60±8.9
2.28±0.4
0.97±0.12
6.21±0.82
54.00 ± 6
61.00 ± 4.6
20.30±2.14
7.88±0.12
-127.00±10.2
2.17±0.7
0.88±0.08
3.12±0.75
138.00 ± 36
41.00 ± 5
15.80±1.98
7.22±0.08
-212.00±28.8
1.65±0.4
0.79±0.06
2.60±0.34
220.00 ± 8
19.00 ± 5
408
INDIAN J. MAR. SCI., VOL. 41 NO. 5 OCTOBER 2012
and aerobic bacterial population. Higher C.F.U of
anaerobic bacteria in LLZ was observed relative to the
aerobic bacterial population where as in ULZ, C.F.U of
aerobic bacteria was found more than that of anaerobic
bacteria. This result strongly indicates that the upper
littoral zone is more oxic than that of lower littoral zone.
In upper littoral zone a significant interaction was seen
between aerobic and anaerobic bacteria which reflects
good environmental health of the ecosystem resulting an
efficient oxidation of the reduced and harmful gases like
hydrogen sulfide, methane etc. in the sediment column
before reaching the environment15. Both the lower
littoral and middle littoral zone showed more population
of methanogens than methanotroph which could convert
the system as a net emitter of methane to the
atmosphere. The methanogenic bacterial population
depends on temperature, pH, redox potential and salinity
of the water and sediments16. The presence of sulphate
reducing bacteria limits the proliferation of
methanogens17. Sulfate and nitrate concentration was
found to show an increasing trend from LLZ to ULZ
which is reflected in Fig. 4 and Fig. 5 respectively.
Fig 4 Mean C.F.U of aerobic and anaerobic bacteria in different
sulfate Concentration in three zones
During transportation from riverine system to terrestrial
environment biomineralization are slowly performed on
the way by the decomposers which may contribute more
nitrate and sulfate to the ULZ than that of LLZ.
Population of aerobic bacteria showed increasing trend
from LLZ to ULZ where as reverse profile was found
for anaerobic bacteria18. found higher population of
anaerobic bacteria in the sulfate rich sediment
dominated by Avecennia marina. Mangrove
sediments are mainly anaerobic with an overlying thin
aerobic sediment layer. Degradation of organic matter
in the aerobic zones occurs principally through
aerobic respiration whereas in the anaerobic layer
decomposition occurs mainly through sulphate
reduction19, 20. The availability of iron and
phosphorous in mangrove sediments may depend on
the activity of sulphate reducing bacteria20. In
Florida’s mangrove sediments contained a significant
population of sulphate reducing bacteria were also
able to fix N221. This present study supported this
observation. Benner et al. (1984)22 and Lee (1992)23
found that in any sediment column rate of
decomposition of organic matter by aerobic bacteria
was more than that of anaerobic bacteria. Our present
study supported this surveillance because in the
present study the population of anaerobic bacteria was
found to show a decreasing trend with increase in
organic matter content of the soil sample of LLZ,
MLZ and ULZ respectively. A reverse profile was
found for the population of aerobic bacteria (Fig. 6).
Higher population of aerobic bacteria in the sediment
of more organic matter may be due to faster
decomposition rate24. Salinity of soil sample was
found to show an increasing trend from LLZ to ULZ.
At the same salinity of LLZ region population
of anaerobic bacteria was found to be more in
Fig 5 Mean C.F.U of aerobic and anaerobic bacteria in different
N-NO3- concentration in three zones
Fig 6 Mean C.F.U of aerobic and anaerobic bacteria in different
organic matter concentration in three different zones
DAS et al.: DISTRIBUTION OF AEROBIC AND ANAEROBIC BACTERIA IN SUNDERBAN MANGROVE ECOSYSTEMS
409
Fig7 Mean C.F.U of aerobic and anaerobic bacteria in different
salinity in three different zones
et al (2000)26 the optimum range of pH for anaerobic
methanogen in mangrove sediment varied between
6.5 and 7.5. In this present study identical observation
was found. Soil sample collected from LLZ with
relatively lower pH value of 7.22 was dominated by
higher number of anaerobic bacteria than that of
aerobic bacteria (Fig. 8). On the contrary, in the
sediment collected from ULZ with mean pH value of
8.01, slight dominance of the aerobic bacteria was
recorded over their anaerobic counterpart. Influence
of salinity on the growth rate of both aerobic and
anaerobic bacteria was examined by growing them in
the selective medium with different salinity of
10, 15, 20, and 25 PSU which is represented in Fig. 9.
A consistent interaction was found between aerobic
and anaerobic bacteria near salinity range between 22
and 24 PSU. On the other hand an inconsequential
interaction was recorded in the rest part of the salinity
range. Variation in soil salinity was found more in
surface sediment (aerobic) than the bottom
(anaerobic) sediments which was collected below the
30 cm from the surface. This was due to the routine
effect of high tide and low tide affecting the surface
more efficiently than the deeper part. This indicates
that the growth rate of aerobic bacteria was more
influenced by daily variation of salinity whereas
anaerobic bacteria were less influenced. It can also be
said from Fig. 9 that the aerobic bacteria are more
sensitive to variation in salinity than that of anaerobic
bacteria. These observations were found similar to
that by Rietz and Haynes et al. (2003)27 in wetland
sediment. Aerobic bacteria are less resistant to salinity
fluctuation25, which in turn may hamper oxidation
process of methane. This may cause more methane
emission than the carbon dioxide from the sediment.
Fig 8 Mean C.F.U of aerobic and anaerobic bacteria in different
pH value in three zones
Fig 9 Effect of salinity on growth of both aerobic and anaerobic
bacteria
comparison with population of aerobic bacteria. Same
profile was also found in MLZ. This observation can
be explained from the study by Lowe et al. (1993)25.
According to their report it can be predicted that
anaerobic bacteria can grow at environmental
extremes of temperature, pH, salinity, substrate
toxicity, or available free energy and anaerobes,
unlike aerobes, appear to have evolved more energyconserving mechanisms for physiological adaptation
to environmental stresses such as novel enzyme
activities and stabilities and novel membrane lipid
compositions and functions. In upper littoral zone
salinity was found to be maximum but population of
aerobic bacteria was found to be little more than that
of anaerobic bacteria. It can be explained by the fact
that the ULZ remains exposed maximum period of
time to cause oxic environment which may promote
the growth of aerobic bacteria even with higher
salinity zone (Fig. 7). Sediment profile of different
tidal zone showed an increasing trend for pH value
from LLZ to ULZ. According to the study by Lyimo
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INDIAN J. MAR. SCI., VOL. 41 NO. 5 OCTOBER 2012
Any perturbation in the sediment biogeochemistry of
Sunderban mangrove forest due to climate change
may alter the magnitude of methane emission from
the biosphere than present.
Organic matter showed prominent effect on the
growth rate of both for aerobic and anaerobic
bacteria28. It is well documented in several reports
that more the organic carbon in the sediment more
would be the consumption of oxygen. This in turn
favors the growth of anaerobic bacteria but inhibits
growth of aerobic bacteria. Organic products from
mangrove litter falls and other anthropogenic sources
increase concentration of organic carbon in soil. This
supply of organic carbon along with enhanced
submergence of mangrove sediment due to sea level
rise could fuel the anoxic condition of mangrove
sediment. This may result a higher growth rate of
anaerobic bacteria than the aerobic bacteria in this
wetland sediment. Production of methane may also
get increase by several times than its consumption by
aerobic bacteria. As a result Sunderban mangrove
forest may act as stronger net emitter of methane to
the atmosphere than the present.
Conclusion
Mangrove ecosystem provides shelter and
nurturing sites for many marine micro organisms. The
present study of interaction between aerobic and
anaerobic bacteria present in sediment of NE Coast of
Bay of Bengal infers the following. Viable count of
both aerobic and anaerobic bacteria in coastal zone
replicates the depth profile of soil biogeochemical
characteristics regarding oxic and anoxic conditions.
Thus microbiological study on soil sample will be an
effective clue for determination of soil quality.
Organic waste product must be treated properly
before discharging into natural body of water;
otherwise such organic waste will make the
environment ideal for the methanogenic bacteria
causing more emission of methane from wetland soil
to the atmosphere. Anaerobic bacteria are more
resistant to the soil salinity fluctuation than that of
aerobic bacteria. Sea level rising due to global
warming may cause fluctuation of water as well as
soil salinity which may ultimately hamper the activity
of aerobic bacteria a little more than that of anaerobic
bacteria. Thus oxidation of the reduced trace gas like
methane by aerobic bacteria like methanotrophs could
be hindered more than that of in present. In such
condition mangrove sediment may emit more
methane to the atmosphere. Sea level rise due to
global warming may act adversely to the stable
ecological zone of Sunderban Mangrove Forest which
may ultimately reflect to net flux of several
biologically active trace gases between soil and
atmosphere.
Acknowledgments
The financial assistance from Department of
Science and Technology, New Delhi, Govt. of India
and Department of Environment, Govt. of West
Bengal, are gratefully acknowledged. Authors are also
grateful to the Forest Department, Govt. of
West Bengal for assisting the research team in
collecting data and providing all infrastructural
facilities to reach the remote island.
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