Salt tolerant culturable microbes accessible in the soil of the Sundarban Mangrove forest, India

doi:10.4236/oje.2011.12004

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Vol.1, No.2, 35-40 (2011)

http://dx.doi.org/10.4236/oje.2011.12004

Open Journal of Ecology

Salt tolerant culturable microbes accessible in the soil

of the Sundarban Mangrove forest, India

Subhajit Das1*, Minati De2, Raghab Ray1, Dipnarayan Ganguly1, Tapan Kumar Jana1, Tarun

Kumar De1

1Department of Marine Science, University of Calcutta, Calcutta, India; *Corr esponding Author: [email protected]

2Maniktala Siksha Bhavan, Calcutta.

Received 20 May 2011; revised 20 June 2011; accepted 30 June 2011.

ABSTRACT

Sundarban Mangrove forest is highly productive

marine ecosystem where halophilic microbes

actively participate in bio-mineralization and

biotransformation of minerals. The population

of aerobic halophilic microbes was studied to

determine their distribution with the availability

of different physicochemical parameters with

increasing depth of this forest sediment. The

present study revealed that microbes present in

the top soil region w ere less tolerant to fluctua-

tion in salinity than the middle and bottom

segment. Microbes isolated from bottom seg-

ment showed higher growth rate in anaerobic

condition. A decreasing trend of total microbial

population and organic carbon content of soil

were found with increase in depth. In contrary a

reverse profile was found for salinity. A signifi-

cant stratification was found to exist among

microbial population and the salty nature of the

soil of Sundarban Mangrove forest.

Keywords: Sundarban Mangrove Forest;

Ecosystem; Halophilic Microbes; Aerobic Condition;

Anaerobic Cond i ti o n

1. INTRODUCTION

Some studies investigated the impacts of soil saliniza-

tion on the microbial community and found that in-

creasing salt levels had a significant negative impact on

microbial populations. Yuan et al. [1] found that there

was a significant negative exponential relationship be-

tween soil salinity and soil microbial biomass and basal

soil respiration.

The distribution of microbial activities in estuarine

systems is clearly complex and variable. Much research

remains to be done in order to define the distributions of

microbial activities and the major factors involved in

controlling these distributions in mangrove dominated

tropical estuaries. Salinity and sodicity properties of

coastal soil determine the degrees of inhibition of mi-

crobial activity and biochemical processes that are fun-

damental in maintaining ecological quality and produc-

tivity in soils of coastal regions [2]. Major products of

general recycling of organic matter are detritus which is

rich in enzymes and proteins and contains large micro-

bial population [3]. Microbial compositions are the ma-

jor participants in the carbon, sulphur, nitrogen and

phosphorous cycles in mangrove forest [4-6]. Microbial

activity is responsible for most of the carbon recycling in

mangrove sediment under both in oxic and anoxic condi-

tion. Many species of phosphat e sol ubilizi ng

rhizosphere

bacteria associated with black mangrove roots were

found from the prev ious research works. The mechanism

for phosphate solubilization probably involves the pro-

duction of several organic acids [5]. Effects of NaCl,

salinity (EC 5, 10, 15 dSm–1) were studied on the popu-

lations of ammonium oxidizers, nitrite oxidizers and

Azotobacter in rice rhizosphere in a pot-culture experi-

ment. Increasing salinity reduced the population of both

the groups of nitrifying bacteria. The growth rate of

4 ox idizers was found to be more susceptib le to salt

stress than 4 oxidizers [7]. Halophilic and halotol-

erant microorganisms are able to thrive and grow in sa-

line and hypersaline environments. These microorgan-

isms are being the object of basic studies in relation to

the origin of life in our planet and the molecular mecha-

nisms of adaptation to saline and hypersaline conditions

[8]. Most investigation of anaerobic metabolism in natu-

ral ecosystem have dealt with sulfate rich marine sedi-

ments where sulfate reduction is the dominating process

or eutrophic lake sediments where sulfate and nitrate is

depleted in the hypolimnionn and in the superficial

sediment layers leaving terminal carbon mineralization

principally to methan e producing bacteria [9-11]. Sulfate

NH +

S. Das et al. / Open Journal of Ecology 1 (2011) 35-40

reduction, methane production, de-nitrification were the

important processes for the terminal electron removal

during decomposition of organic matter in anoxic envi-

ronment.

The methanogens are characterized by their ability to

produce methane from hydrogen and carbondioxide,

formate, acetate, methanol etc [12]. Methanotrophs are a

subset of a physiological group of bacteria known as

methylotrophs. They are unique in their ability to utilize

methane as a source of carbon and energy [13]. Nitrogen

fixing bacteria are the other group of bacteria that are

involved in formation of ammonia or organic nitrogen

from atmospheric nitrogen. It has been studied that N2

fixation by heterotrophic bacteria are generally regulated

by specific environmental factors like oxygen, combined

Nitrogen and the availab ility of carbon source fo r energy

requirement [14]. Aerobic, autotrophic nitrifiers oxidize

ammonia to nitrite and nitrate, with molecular ox ygen as

electron acceptor. Nitrite and nitrate are reduced to

di-nitrogen gas by heterotrophic denitrifying bacteria

that use NOx instead of oxygen as electron acceptor [15].

The coastal wetland forests con sists of intertidal zon es

of estuaries, brackish waters, deltas, creeks, lagoons

marshes and mudflats of tropical and subtropical lati-

tudes are called as Mangroves. Mangrove forests are

usually considered to be high productive areas that sup-

port highly developed detritus-based food webs. The

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 recycling. The organisms

within mangrove ecosystems, including microorganisms,

plants and animals, show complex interactions. Micro-

organisms 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. Therefore,

Mangrove provides a unique ecological niche to differ-

ent microbes, which play various roles in nutrient recy-

cling as well as different environmental activities. The

decomposition involves in this forest at various trophic

groups of microorganisms acting in a multi-step process.

The first step is an enzymatic hydrolysis of polymeric

material to soluble monomeric and oligomeric com-

pounds. 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 de-

polymerisation. Fermentative bacteria convert the prod-

ucts 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 produce

the end products as CO2, CH4 and H2S, which may es-

cape into the atmosphere. First two gases among them

are important greenhouse gases. The organisms within

mangrove ecosystems, including microorganisms, plants

and animals, show complex interactions. Microorgan-

isms 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. Distribution of bac-

teria depends on changes in water temperature, salinity

and other physico-chemical parameters [16]. Due to high

salinity, halophilic bacteria are believed to be predomi-

nant in this ecosystem. It serves as important source of

food for a variety of marine organisms and maintains

pristine nature of the environment. It also acts as a bio-

logical mediator through their involvement in the

bio-geochemical process [17]. In the present study an

attempt has been taken to explore the vertical distribu-

tion of microbial population along with different phys-

icochemical parameters of the soil and their response to

fluctuation in salinity an d availability of O2.

2. MATERIALS AND METHODS

2.1. Study Area

Sundarban Mangrove forest that is located geographi-

cally in between 21˚31´N and 22˚30´N and longitude

88˚10´E and 89˚51´E along the North East coast of Bay

of Bengal, India. Sampling zone of present study is rep-

resented in Figure 1.

This mangrove forest is a part of the estuarine system

of the River Ganges, NE coast of Bay of Bengal, which

covers 9630 km2, out of which 4264 km2 of inter-tidal

Figure 1. The map presenting the zone of the present study.

S. Das et al. / Open Journal of Ecology 1 (2011) 35-40 37

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 com-

plex is semidiurnal in nature with spring tide range be-

tween 4.27 and 4.75 m and neap tide range between 1.83

and 2.83 m. It is a unique bioclimatic zone in land o cean

boundaries of Bay of Bengal and the largest delta on the

globe. Several numbers of discrete islands constitute

Sundarbans. One of these Islands, Lothian Island cover-

ing an area of 38 km2 has been notified as a sanctuary

and is situated at the confluence of Saptamukhi River

and 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 offici-

nalis 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 Sundarban Biosphere Reserve com-

prises mainly with saline alluvial soil consisting of clay,

silt, fine sand and coarse sand p articles. It is described as

very deep, poorly drained, fine soils occurring on level

to nearly level lower delta with loamy surface, severe

flooding and very strong salinity (extensive extent) as-

sociated with very deep, very poorly drained, fine loamy

soil.

2.2. Soil Sample Collection

Triplicate soil samples were collected aseptically from

three different depths ranging from 0 - 10, 10 - 20 and

20 - 30 cm as top, middle and bottom segments respec-

tively using a hand-held soil corer. The samples were

collected in sterilized polythene containers and trans-

ported to the laboratory in iced co ndition without delay.

2.3. Quantification of Bacteria

Separately, from each replicate, 10 g·m of aliquot

sample from different soil segment was homogenized

with sterilized phosphate buffer solution (PBS). Serial

dilutions upto 1 0–4 were made and inoculation was done

with 0.1ml. Quantification of bacteria from mangrove

sediments was carried out by spread plate method in

Marine Agar 2216 Medium [18] under incubation for 24

hours at 32˚C temperature.

2.4. Sediment Quality Measurement

From aliquot soil sample 30 g of subsample was

added in 75 ml of 2 mol·L–1 potassium chloride (KCl).

The mixture was shaken un til well mixed and allowed to

stand overnight [15]. After 24 h, 4 ml of the supernatant

was collected for the estimation of Nitrate-Nitrogen and

Phosphate-Phosphorous of the soil sample using stan-

dard spectrophotometric methods [19].

For estimation of Sulfate-Sulfer concentration in the

soil sample, 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 (0.45 m). The

filtrate was used to determine sulphate concentration

turbidometrically [20]. Soil was dissolved in distilled

water and chlorinity (Cl) of the water were determined

by Mohr-Knudsen titration method and standard sea-

water of chlorinity 19.374 procured from the National

Institute of Oceanography, Goa, was used for the stan-

dardization. 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) [21].The organic

matter was determined by the modified Wakly-Black

method (oxidation with potassium dichromate in sul-

phuric acid solution) to obtain organic carbon [22].

2.5. Enumeration of Viable Count of

Microbes in Different Salinity

After extraction of soil from 3 distinct zones with PBS,

inoculations with 0.1 ml were done into Marine Agar

2216 medium with different salinity. After same incuba-

tion period CFU we re counted sepa rately for each distinct

zone.

2.6. Measurement of Growth Rate of

Microbes Found from Three Distinct Soil

Segments in Aerobic and Anaerobic

Condition

After extraction of soil from 3 distinct zones with PBS,

inoculations with 0.1 ml were done into Marine Agar

2216 medium and they were allowed to grow separately

in aerobic and anaerobic condition. After each 12 hour

interval CFU of microbes were counted.

3. RESULT & DISCUSSION

In recent work it was found to show a decreasing

trend of total organic carbon content of soil with in-

crease in depth (1.08 ± 0.209% in top soil segment, 1.01

± 0.186% in bottom soil segment and 0.9 ± 0.115% in

bottom soil segment). Similar type of profile was found

for phosphate-phosphorous ( 0.438 ± 0.167 µg·gm–1 dry

weight of soil in the top soil segment, 0.389 ± 0.142

µg·gm–1 dry weight of soil in the middle soil segment

and 0.359 ± 0.116 µg·gm–1 dry weight of soil in the bot-

tom soil segment) and sulfate-sulfur concentration (1.39

± 0.329 mg·gm–1 dry weight of soil in the top soil seg-

ment, 1.22 ± 0.257 mg·gm–1 dry weight of soil in the

middle soil segment and 1.14 ± 0.191 mg·gm–1 dry

S. Das et al. / Open Journal of Ecology 1 (2011) 35-40

weight of soil in the bottom soil segment). From top to

middle soil segment a decreasing trend was found for ni-

trate-nitrogen concentration (0.194 ± 0.014 µg·gm–1 dry

weight of soil in the top soil segment and 0.178 ± 0.01

µg·gm–1 dry weight of soil in the middle soil segment).

Bottom soil segment (0.185 ± 0.026 µg·gm–1 dry weight

of soil) was found to show a little increase in ni-

trate-nitrogen concentration. Soil temperature (18.58 ±

4.813˚C, 18.56 ± 4.926˚C and 18.44 ± 4.827˚C in top

soil segment, middle soil segment and bottom soil seg-

ment respectively) and population of culturable microbes

(12.437 ± 0.821 × 106 CFU gm–1 dry weight of top soil

segment, 10.966 ± 0.725 × 106 CFU gm–1 dry weight of

middle soil segment and 9.647 ± 0.788 × 106 CFU gm–1

dry weight of bottom soil segment) were found to de-

crease from top to bottom soil segment. Huge population

of halophilic microbes found in present study from the

soil of Sundarban mangrove forest may be supported by

Kathiresam, K in 2001, [23] for predicting microbial

(Halophilic aerobic bacterial) load as it gives too nu-

merous to count (TNTC) colonies even at 10–8 dilution.

Maximum salinity of soil was found for bottom segment

(16.37 ± 0.546 psu) following middle segment (15.23 ±

0.403 psu) ant top soil segment (11.6 ± 1.41 psu). On

contrary middle soil segment showed maximum of soil

pH value (8.28 ± 0.086) following bottom segment (8.24

± 0.058) and top soil segment (8.19 ± 0.197) (Table 1.).

The organisms from the three different segments were

allowed to grow on salinity of 0.5, 1, 1.5 upto 4 (%)

modified marine agar medium. Among the three seg-

ments studied, the bottom segment showed higher halo-

philic microbial load with medium of increasing salinity

and middle segment showed insignificant variation. Sur-

prisingly, microbes isolated from top segment showed a

decreasing trend of their population with increasing sa-

linity (Figure 2).

The above mentioned result evoked the urihaline na-

ture [24] of microbes present in the top soil segment.

Microbes isolated from top segment was found to show

maximum growth rate when they were allowed to grow

in aerobic condition. It may be attributed that aerobic

microbes were dominant in 0 - 10 cm top soil segment

[3]. In contrary a reverse profile was found for microbes

isolated from bottom segment (Figure 3).

The bottom segment was found to show maximum

growth rate compare to middle and top soil segment

when the microbes isolated from three segments were

allowed to grow in anaerobic condition (Figure 4).

It may be attributed that anoxicity increases with

depth and anaerobic microbial population was dominant

in the bottom soil segment [25]. Recent study revealed

that anaerobic microbes present in the bottom segment

are more tolerant to fluctuation of salinity in the sur-

Table 1. Physico-chemical parameters & microbial load in

different depth of mangrove soil.

Top soil Middle soil Bottom soil

Physicochemical

Parameters and

microbial load Avg± stdv Avg ± stdv Avg± stdv

Salinity (PSU) 11.61.41 15.23 0.403 16.370.546

pH 8.190.197 8.28 0.086 8.240.058

Temp (ºC) 18.584.813 18.56 4.926 18.444.827

Org.C (%) 1.080.209 1.01 0.186 0.900.115

N-NO3- µg·gm–1 dry wt o

sediment 0.194 0.014 0.178 0.01 0.1850.026

S-SO4–2 mg·gm–1 dry wt

of sediment 1.390.329 1.22 0.257 1.140.191

P-PO4–3µg·gm–1 dry wt of

sediment 0.438 0.167 0.389 0.142 0.3590.116

Microbial C.F.U (× 106)

gm–1 dry wt of sediment12.437 0.821 10.966 0.725 9.6470.788

Effec t of salinit

o n mic ro bial populatio n

012345

Salinity of the medium

Micro bial CFU

TopSoil

Middle Soil

B ottomSoil

Figure 2 . Variation of microbial CFU (× 106 gm–1 dry weight of

soil) of three soil segment with medium having different

salinity.

Micro bial growt h of 3 so il segmen t in a erobic condition

0 20406080

Incubation Period ( hour)

CFU X10

-1

dry weight of soi

TopSoil

Mid dleSoil

BottomSoil

Figure 3. Growth rate of microbes from 3 soil segments in

aerobic condition.

S. Das et al. / Open Journal of Ecology 1 (2011) 35-40 39

Mic r obial growth of 3 so il segment in anaerobic c on dit ion

0 20406080

I ncubation Period (hour)

CFU X10

-1

dry w e ight of soil

TopSoil

Midd leSoil

B ottomSoil

Figure 4. Growth rate of microbes from 3 soil segments in

anaerobic condition.

rounding environment than the aerobic microbes present

in the top soil segment. This observation can be ex-

plained from the study by Lowe et al. [26]. 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

energy-conserving mechanisms for physiological adapta-

tion to environmental stresses such as novel enzyme ac-

tivities and stabilities and novel membrane lipid compo-

sitions and functions. 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 bac-

teria. Soil salinity is a stress factor relating to microbial

selection process and can reduce bacterial diversity and

control microbial abundance, composition and functions

[27]. Thus oxidation of the reduced trace gas like meth-

ane by aerobic bacteria like methanotrops could be hin-

dered more than that of in present. In such condition

mangrove sediment may emit more methane to the at-

mosphere.

4. CONCLUSIONS

This bacterial growth profile study reveals that a per-

fect stratification exists between the depths of soil in the

mangrove ecosystem and salt tolerance nature of the

bacteria. This stratification may be responsible for a

perfect nutritive management of the mangrove forests.

Thus they provide unique ecological niche to variety of

microorganisms. More anoxic and salty nature of the

Sundarban Mangrove Forest may play a crucial role to

reflect on the microbial activity regarding biogeochemi-

cal cycles.

5. ACKNOWLEDGEMENTS

We would like to acknowledge UGC, New Delhi for providing fel-

lowship to Sudhajit Das and department of forest, Govt. of West Ben-

gal for permitting us to do this study in Sundarban mangrove forest.

REFERENCES

[1] Yuan, B.C., Li, Z.Z., Liu, H., Gao, M. and Zhang, Y.Y.

(2007) Microbial biomass and activity in salt affected

soils under arid conditions. Applied Soil Ecology, 35,

319-328. doi:10.1016/j.apsoil.2006.07.004

[2] Siddikee, M., Ashaduzzamanl, Sherlyn, C., Tipayno1,

Kiyoon, K., Jongbae, C. and Tongmin, S. (2011) Influen-

ce of varying degree of salinity-sodicity stress on enzyme

activities and bacterial populations of coastal soils of

yellow sea, South Korea. Journal of Microbiology and

Biotechnology, 21, 341-346.

[3] Holguin, G., Bashan, Y. and Vazavez, P. (2001). The

role of sediment microorganism in the productivity,

conservation and rehabilitation of mangrove ecosystem:

an overview. Biology of Fe rtile Soils, 33, 265-278.

doi:10.1007/s003740000319

[4] Toledo, G., Bashan, Y. and Soeldner, A. (1995) Cyanob-

acteria and black mangroves in Northwestern Mexico:

colonization, and diurnal and seasonal nitrogen fixation

on aerial roots. Candian Journal of Microbiology, 41,

999-1011. doi:10.1139/m95-139

[5] Vazquez, P., Holguin, G., Puente, M.E., Lopez-Cortes, A.

a nd Bas ha n, Y. ( 200 0) Ph osphate-solub ilizing m icroorga-

nisms associated with the rhizosphere of mangroves in a

semiarid coastal lagoon. Biology of Fertile Soils, 30, 460-

468. doi:10.1007/s003740050024

[6] Rojas, A., Holguin, G., Glick, B.R. and Bashan, Y. (2001)

Synergism between Phyllobacterium sp. (N2-fixer) and

Bacillus licheniformis (P-solubilizer), both from a sem-

iarid mangrove rhizosphere. FEMS Microbiology Eco-

logy, 35, 181-187.

doi:10.1111/j.1574-6941.2001.tb00802.x

[7] Kaushik, A., and Sethi, V. (2005) Salinity effects on

nitrifying and free diazotrophic bacterial populations in

the rhizosphere of rice. Bulletin of the National Institute

of Ecology, 15, 139-144.

[8] DasSarma S. and Arora, P. (2002) Halophiles; in encyc-

lopedia of life sciences, Nature Publishing Group,

London, 8, 458-466.

[9] Senior; E., Lindstrom, E.B., Banat, I.M. and Nedwell,

D.B. (1982). Sulfate reduction and mathanogenesis in the

sediment of a saltmarsh on the eastcoast of the United

Kingdom. Applied Environ Microbiol, 43, 987-996.

[10] Sorensen, J., Jorgensen, B.B. and Revsbech, N.P. (1979).

A comparison of oxygen, nitrate and sulfate respiration

in coastal marine sediment. Microbial Ecology, 5, 105-

111. doi:10.1007/BF02010501

[11] Lovley, D.R. and Klug, M.J. (1982) Intermediary metab-

olism of organic matter in the sediment of a eutrophic

lake. Applied and Environmental Microbiology, 43, 552-

560.

[12] Mohanraju, R. and Natarajan, R. (1992) Methanogenic

bacteria in mangrove sediments. Hydrobiologia, 247,

187-193. doi:10.1007/BF00008218

[13] Chen-rul, W., Yi, S., Xiao-Ming Y., Jie, W. and Jin Y.

(2003) Advances of study on atmospheric methane

oxidation (consumption) in forest soil. Journal of Forest

Research, 14, 230-238. doi:10.1007/BF02856837

S. Das et al. / Open Journal of Ecology 1 (2011) 35-40

OPEN ACCESS

[14] Teri, C.B. and Mary, K.F. (2005) Linking microbial

community composition and soil processes in a Californ-

ia annual grassland and mixed conifer fore st. Biogeoc-

hemistry, 73, 395-415.

[15] Riley, R.H., Peter, M. and Vitousek, P.M. (1995) Nutrient

dynamics and nitrogen trace gas flux during ecosystem

development in montane rain forest. Ecology, 76, 292-

304. doi:10.2307/1940650.

[16] Alavandi, S. (1990) Relationship between heterotrophic

bacteria and suspended particulate matter in the Arabian

Sea. Indian Journal of Marine Sciences, 30, 89-92.

[17] Capone, D.G. (2002) Microbial nitrogen cycle, in: Manu-

al of environmental microbiology (Ed: C.J. Aurstic and

R.L. Crawford), ASM Press, Washington D.C., 439.

[18] Bianchi, A. and Giuliano, L., (1996) Enumeration of

viable bacteria in the marine pelagic environment,

Applied Environmental Microbiology, 62, 174-177.

[19] Grasshoff, Ehrhardt and Kremling (1983) Standard

methos for sea water analysys, 2nd Edition, Wiley-VCH,

Geman.

[20] American Public Health Association (APHA) (1995)

Standard methods for the examination of water and

wastewater: including bottom sediments and sludges.

American Public Health Association, Washington D.C.

[21] Tiwari, S. C., Tiwari, B. K. and Mishra, R. R (1989)

Microbial community, enzyme activity and CO2

evolution in Pineapple Orchard soil. Tropical Ecology,

30, 265-273.

[22] Walkley, A. and Black, J. A., (1934) An examination of

Degtjareff method for determining soil organic matter,

and a proposed modification of the chromic acid titration

method. Soil Science, 37, 29-38.

[23] Kathiresan, K. (2001) Biology of mangroves and man-

grove ecosystem. In:Advances in marine biology (Ed.:

A.J. Southward), Academic Press, U.K. 81-251.

[24] Odum, E.P. (1971) Fundamentals of ecology. 2nd Edn.,

W.B. Saunders Company and Toppan Company, Phil-

adelphia, U.S.A. 574-575.

[25] Chun-Hua L., Hong-Wei, Z., Yuk-Shan, W. and Nora

Fung-Yee T. (2009) Vertical distribution and anaerobic

biodegradation of polycyclic aromatic hydrocarbons in

mangrove sediments in Hong Kong, South China.

Science of the Total Environment, 407, 5772-5779.

[26] Lowe, S. E, Jain M. K. and Zeikus, J. G. (1993) Biology,

ecology, and biotechnological applications of anaerobic

bacteria adapted to environmental stresses in temperature,

pH, salinity, or substrates. Microbiology and Biotech-

nology Reviews, 57, 451-509.

[27] Moradi1, A., Tahmourespour, A., Mehran Hoodaji, M.

and Khorsandi, F. (2011) Effect of salinity on free

living-diazotroph and total bacterial populations of two

saline soils. African Journal of Microbiology Research, 5,

144-148.