Aquatic Environment

Introduction:

The majority of the earth’s surface is covered of water. Nearly ¾ % of the earth is made

up of hydrosphere. The on going water cycle brings in lot of minerals to the oceans, seas and

the rivers. The input of the various nutrients and biogeochemical cycle enriches the water with

the nutrients. This input of the nutrients in the fresh and marine environments supports the

microbial community in its niche. The organic matter accumulated in the ocean sinks into the

depths of the earth creating nutrient rich environment. This nutrient rich environment

stimulates the growth of the microbial community.

About 98% of the earth is covered by the oceans. the study of marine microbiology

began in the latter part of the 19th century. The Galathea Expedition under taken under the

guidance of Danish government mainly dealt on the study of the marine ecosystem. The

expedition was also an eye opener since many types of microorganisms were discovered. There

were total of three expeditions of which the third took place in the year 2006 the largest one.

All these experiments were focused on the distribution of the micro organisms in the marine

environments.

The recent research analysis shows that the study of aquatic microbiology has been

diverted from the content to the contribution analysis. The study is more oriented in finding out

the involvement of microorganisms in the biogeochemical cycles, microbial symbiosis

nitrogen-fixing bacteria in boring mollusks, photosynthetic organisms in corals, and sulfur-

oxidizing bacteria in hydrothermal-vent organisms, have shown the widespread occurrence of

marine symbiosis. Chemoautotrophic bacterial populations at deep-sea vents in symbiotic

associations with the giant hydrothermal-vent tube worm, Riftia pachyptila.

The temperature and pH also plays a major role in life of the organisms. Hence the

organisms living in different depth are accustomed to adopt for different temperature and pH.

The temperature can range form -5 to -150 c and 1130 c in geothermal areas. The significance of

these obligate pycrophilic microorganisms and their survival at extreme pressures, as

“starvation – survival” and “feast or famine” in the oligotropic conditions opens our horizon

towards a broader perspective in marine microbiology.

Aquatic Environment:

The aquatic environment involves rivers, streams, lakes, seas and oceans. Each of the

following has its own type of environment. They have their own size, geographical location

physical and chemical character. Sunlight, temperature, aeration, and dissolved nutrient content

differe based on their developmental zones. Another factor which contributes the environment

is the constant mixing and movement of the dissolved organic matter. The rivers and streams

will be more fed with the nutrients washed away form the land because of the rain. This type of

aquatic system varies according to the seasons and the availability of water.

The lakes are stratified vertically into 3 zones or strata:

– photic zone – surface to lowest limit of sunlight penetration where most of the

phototropic bacteria grow using co2 and sunlight.

– aphotic zone – edge of the photic zone to lake sediment.

– heterotrophic benthic zone – organic debris and mud forming the basin

I the above two zone of the aquatic environment the aphototropic bacteria which use

sulphur, hydrogen sulphide, carbonates, nitrogen and other organic nutrients.

Stratified horizontally into 2 zones:

– littoral zone – shoreline, relatively shallow water which is rich in dissolved

organic matter.

– pelagic zone – open, deeper water which consist of aphotic and heterotrophic

benthic zones

This example holds good even for the sea and marine environment where the only exception is

that the salinity pH and the temperature varies with that from the lakes. The stratification in the

ocean habitat can be called as pycnocline which means rapid change of density with depth. It

can be explained as follows. Isopycnal surface of constant potential density of water,

thermocline buffer zone between warmest and coolest layers; ordinarily prevents the mixing of

the two, halocline vertical salinity gradient, thermohaline temperature and salt concentration,

and chemocline warmer and cooler water meet. Along with these there are estuaries, the

meeting point between the rivers and seas or oceans where fringing vegetation such as grasses

and mangrove species are vital to the input of nutrients. It is also calls as brackish environment

which means the water is salty from the river water and less salty from the marine water.

Gases :

The two gases of major importance in aquatic environment to microorganisms are

oxygen and carbon dioxide, while nitrogen, methane, phosphorous and other trace gases are of

secondary importance. Microorganisms are involved in most of the geochemical cycles in the

oceans..

OxygenThe oxygen cycle is maintained in tow ways. One is by direct interaction between the

atmosphere and hydrosphere, secondly by the constant interaction of the cyanobacteria leading

to the evolution of oxygen. The solubility of oxygen in aquatic environment is low with high

temperature and low pressure. The use of oxygen by the aquatic organisms from the water

leads to the formation hypoxic or anoxy zones. These zones allow specialized anaerobic

organisms, both chemotropic and phototropic microorganisms to grow

Carbon Cycle:

The carbon dioxide being the second important gas in the aquatic environments

maintains the pH of the water. The carbon-bicarbonate controls the weak or strong buffered

areas. The use of carbon by autotrophic organisms increases the pH of the water. The inflow o

carbon takes place through various processes. The water washed from the land contains

dissolved organic carbon; the weathering of rocks ads carbonates the water, the dead and

decaying organic matter. Oceans also absorb nearly 30-35% of the atmospheric carbon

directly.

Planktons play a major role in the activation of the carbon cycle. They act like a pump

to transport the gases from the surface to the deep. The planktons absorb carbon and store it

like a sink unlike the plants. Most of the gas escapes to the air or it is transported into the

depths via dead plants, body parts faeces and other sinking materials. Marine snow, known as

particulate organic carbon (POC), serves as a vehicle for vertical flux of organic matter and

enriched “hotspots” of microbial respiration and sites of rapid turnover of particulate carbon in

the sea

Nitrogen Cycle:

The nitrogen fixation in the aquatic environment is done by cyanobacteria and bacteria.

The heterocyst’s present in cyanobacteria fix nitrogen and carries out the formation of

nitrogenous compounds. Nitrogen fixation in these organisms requires photosynthetic activity

which means it is light mediated reaction. The recent discoveries show that there are

microorganisms which fix nitrogen in the aquatic environments.

In the aquatic environment assimilation of nitrogen by the autotropes takes place in two

ways: assimilation of dissolved nitrate, nitrite or ammonia and dissolved molecular nitrogen

which is converted into dissolved inorganic nitrogen. The heterotrophic bacteria uptake

nitrogen which is either organic or inorganic. Dissolved organic nitrogen is a heterogeneous

group of organic compounds which is present as urea, ammonia, amino acids, humic and fulvic

acids. Yet large group of microorganisms including protozoa, bacteria and algae assimilate low

molecular weight nitrogenous compound directly. Some of the organisms which fix nitrogen

are Aphanizomenon, Anabaena, Gleotrichia, Nodularia, Cylindrospermum, Synechococcus and

Nostoc

Phosphorus Cycle:

Phosphorus is the essential element in all the living systems. It is the structural

molecule of the cell, storage component and it is also involved in energy transformation. It is

present in the aquatic environment as dissolved organic matter, soluble and insoluble organic

matter. The phosphorus taken up by the phytoplankton moves through internal loading to the

food chain or gets sediment at the bottom of the sea as dead algal cells. The phosphorus which

entered the food chain returns back as biomass. In both the cases it ultimately passes back to

the water column. Phosphorus dose not have a gaseous cycle. The lack of phosphorus is

compensated by nitrogen in the aquatic environment. Phosphorous is also added from the

external environment through the runoff water.

Methane cycle:Methane thus is ideal microbial waste product. It is produced under anaerobic

conditions. It is released vertically to the environment through water column through oxidation

and reduction by bacteria. Hence there is very less toxic waste created by microbes. The

methanogenic bacteria use hydrogen and carbon dioxide to give methane. Even the Sulfate-

reducing bacteria outcompete methanogens for substrates, inhibiting methanogenesis

Nutrients:

The nutrient taking rates in the in the aquatic environment depend on the type of

environment under study. The nutrients in take in marsh and esturain environment have a

rapid rate of nutrient turnover than that of the marine environments. The estuarine and marsh

environments are rich in C: N: P ratio which forms the larger breeding ground for the micro

organisms. The oceans cover the large area and the water in flow dose not meet the needs of

the marine flora which makes marine environment different from that of fresh water

environment.

The microbial loop plays a major role in the circulation of the essential nutrients

required by the aquatic organisms. The communities involved in the microbial loop are

nanoplanktonic algae, microflagelates, picoplanktonic and phytoplanktonic microorganisms.

The microorganisms are the major contributors of the nutrients as they convert the organic

nutrients and dissolved organic matter into living biomass and particulate carbon which can be

called as dissolved organic matter (DOM) and particulate organic matter (POM). The bacteria

are consumed by protozoans and metazoans; they in turn are consumed by zooplanktons that

are later consumed by top consumers. Hence the top consumers are later added into the

microbial loop.

The discovery of the deep hydro thermal vents where the chemoautotrophic bacteria

utilizing H2S as the prime source of energy. The symbiotic relation ship between bioluminous

bacteria and luciferase with various marine mammals, vibrio symbionts with various species of

squids and other relations shows the symbiotic relationship between bacteria and marine

organisms show the food web as a symbiotic relation.

Redfield ratio is the percentage of C: N: P ratio required for the nutrient dynamics.

With this ratio we can study the mineralization, immobilization and various factors responsible

for the microbial growth. We also come to know the sensitivity of the oceanic photosynthesis

and addition of nitrogen, sulphur and iron.

Effect of Pollution on the Marine Environment:

The massive input of organic matter can cause damage to the microbial loop since it

decreases the availability of light for the organisms to grow. This can pose danger since it

damages the oxygen input to the microbial loop. The increase of pollutants may also lead to

eutrophication. Eutrophication also causes algal bloom, decreases biodiversity and induces

toxic waste to the aquatic environment making the environment unfit for the microorganisms.

The over exposure of the phytoplankton’s to the UV-B radiation hampers the growth in

the marine environment. This causes decrease in the colour dissolved organic matter content

(CDOM). The decrease in CDOM increases the UV-B penetration in the aquatic environment.

The radiation causes photodegradartion of the dissolved organic matter. The less availability in

the dissolved organic matter affects the biogeochemical cycles maintained by the

microorganisms in the aquatic environment.

Conclusion: “It has taken marine researchers a long time to fully recognize the greatness of

smallness—to appreciate that the ecological dynamics of life processes are first of all linked to

and directed by the activities of microorganisms. It is in the microbial realm that the scene for

the unfolding of more complex expressions of life is set, where the basic driving forces of

ecology are at home.” With this quote I summarize that these few pages of brief study of the

concepts like aquatic environment, gases in aquatic environment, nutrients in aquatic

environment and effect of pollution on the marine environment is a review of the ‘greatness of

smallness’ of the microorganisms which are inter linked in every aspects of human relation.

Vast amount of microbial wealth is hidden in the unwritten lines of the history of the microbial

history. It is we as microbiologists need to walk into history and carve a niche in this diversity

of microbial world.

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