Microbial adaptation to Marine and Freshwater Environments:
Marine and freshwater environments have diverse surface areas and volumes. They are found in location as varied as human body, beverages and usual places one would anticipate- rivers, lakes and oceans. They also take place in water- saturated zones in materials. These environments can range from alkaline to very acidic, with temperatures from -5 to -15oc at lower range, to at least 121oc in geothermal area. Few of the most fascinating microbes have come from study of high temperature environments, comprising now classic studies of Thomas Brock and his co-workers at Yellowstone National Park.
Their work guided to discovery of Thermus aquaticus, the source of temperature-stable DNA polymerase that makes Polymerase Chain Reaction (PCR) possible. Additionally to temperature, penetration of sunlight and mixing of nutrients, oxygen and waste products which take place in freshwater and marine environments are main factors managing microbial community. Water gives the environment in which an extensive variety of microorganisms survives and functions. Microbial diversity relies on available nutrients, their diverse concentrations, transition from oxic to anoxic zone and addition of electron donors and acceptors in the dynamic environment. Additionally, penetration of light in several anoxic zones develops environments for certain kinds of photosynthetic micro-organisms. One of the adaptations of marine micro-organisms is how tiny most oceanic microbes are. They are so tiny that not until development of very fine filtration systems and the application of direct counting methods (like epiflourescence microscopy) that plenty of ultramicrobacteria was found. The small size is the adaptation as microbial cells should incorporate all nutrients across the plasma membrane.
Cells with the large surface area compared with their total intercellular volume are able to maximize nutrients uptake and can thus grow more rapidly than their larger neighbors. Therefore, most of microbes growing in nutrient- limited or oligotrophic open oceans are between 0.3 micrometer and 0.6 micrometer. Such microbes have developed to maximize their surface area to volume ratio to oligotrophic conditions. At the other extreme is usual marine microbe found off the coast of Namibia in West Africa. Thiomargarita namibiensis, that means "Sulphur pearl of Namibia" is regarded as the world's largest bacterium. Individual cells are generally 100-300 micrometer in diameter. Sulfide and nitrate are utilized by organism as electron door and acceptor respectively. In this situation, nitrate from the overlying seawater, penetrates anoxic sulfide-containing mud' only in storms. When this short term mixing takes place, Thiomargarita takes up and stores the nitrate in the large internal vacuole that occupies 98% of the organism's volume. Vascular nitrate can approach the concentration of 800mili micron. The elementary sulfur granules come out near the cell edge in the thin layer of cytoplasm. Between storms, the organism lives using the stored nitrate as the electron acceptor. These unique bacteria are significant in sulfur and nitrogen cycling in the environments. Another significant adaptation of micro-organisms in aquatic systems is the skill to link and employ resources which are in separate locations or which are available at the similar location only for short intervals like during storms. One exciting bacterium linking extensively separated resources in Thioploca species (spaghetti bacterium) that lives in bundles enclosed by the common sheath. These microbes are discovered all along the coast of Chile, where oxygen poor, nitrate rich waters are in contact with sulfide - rich bottom mud. The similar case attains in coast of West Africa. Such bacteria form filamentous sheath structures, and individual cells can slide 5-15cm deep in sulfide- rich sediments. Again, Zoosporic organisms adapt to life in the water by having asexual reproductive spores with the single whiplash flagellum like chytrids. Another significant group is filamentatous fungi which sporulate under water. These hyphomycetes comprise "Ingoldian fungi" named after C.T Ingold in 1942. Ecology of the aquatic fungi is very appealing. They generate unique tetraradiate conidium on vegetative mycelium that grows inside decomposing leaves. When the vegetative hyphae distinguish in the aerial mycelium, conidia are released in water. Released conidia are then transported and frequently are present in surface foams. When they contact leaves, conidia attach and established new centers of growth. It is significant to note that approx 97% of the Earth's water is in marine environment (estuaries, open oceans and dark cold high pressure benthos) much of which is in the deep sea.
The estuary is the semi enclosed coastal region where the river meets the sea. They are stated by tidal mixing between fresh-water and salt water. They feature the trait salinity profile known as a "salt wedge". Salt wedges are formed as salt is denser than freshwater, so sea water sinks below overlying freshwater. As contribution from freshwater increases, and that of ocean declines, the relative amount of seawater declines with estuary's increased distance from the sea. The distance the salt wedge interferes the estuary is not static. Most estuaries suffer large scale tidal flushings and this compels organisms to adapt to changes in salt concentrations on the daily basis. Microbes living under such conditions combat resulting osmotic stress by adjusting the intracellular osmolarity to limit difference with that of the adjoining water. Most protists and fungi generate osmotically active carbohydrates for this reason; while prokaryotic microbes control internal concentrations of potasium or special amino acids (ecoine and betaine). Most other microbes which inhabit estuaries are halotolerant, distinct from halophilic. Halotolerant microbes can survive important changes in salinity, halophilic micro-organisms have the complete necessity for high salt concentrations.
Estuaries are unique in several respects. Their calm nutrient-rich waters act as nurseries for juvenile forms of several commercially significant fish and invertebrates. Though, they are the most polluted marine environments. They are the final receivers of wastes which are dumped in rivers, and pollutants discharged from industries.
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