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Bacterial Flora of the Sea |
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Bacterial Flora of the Sea
They are more abundant near the shore particularly in polluted areas. They are sparsest at great depths in open oceans. The generation time of bacteria ranges from less than an hour to months or even longer. The shortest generation time reported is 9.8 minutes for Pseudomonas natrieganus. The most characteristic feature of marine bacteria is their capacity to survive and grow in the sea. In coastal regions (where river water enters the sea) there is no sharp distinction between freshwater forms and marine forms. Excepting spores, most freshwater forms perish within a few hours under oceanic conditions. Certain bacterial endospores or fungal spores seem to survive in a dormant state for prolonged periods.
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The, typical characteristic of marine bacteria are their small size (0.1 mm3) and low DNA content. They are obligately oligotrophic. Most oceanic bacteria grow more slowly and form smaller colonies on submerged slide (a technique used to study the occurrence of marine flora). Oceanic bacteria are more proteolytic than soil bacteria that are saccharolytic and more often they are facultatively aerobic. Most of the marine bacteria liquefy agar.
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Most bioluminescent bacteria come from the sea including the saprophytic, symbiotic and commensal species. Oceanic flora can survive extremely low concentrations of nutrients (20 mg/l) hence they are most often associated with algal surfaces or detrital particles which offer nutritional advantages
Most of the oceanic bacteria grow at 0°C (optima is12-25°C). Heating sea samples for 10 min at 30-40°C kills 80% of the bacteria. Most of the sea flora are barotolerant and grow at pH of 7.2-7.6 at the surface and pH 6.4-9.4 in marine sediments. Marine bacteria have a highly specific need for sodium and chlorine. Some marine bacteria have multiple membranes surrounding their cells. Exposure to fresh water, disrupts these membrane layers causing a loss of viability
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A high percentage of marine bacteria have a tendency to grow attached to solid surfaces (hence submerged slide technique is used extensively to study the occurrence of marine flora). Numerous species are attached to plankton or to larger organisms.
The highest biomass of microflora in marine waters is normally seen near the surface and they decrease with depth. Some microflora growing in the surface go more downwards often attached to sediment particles. They provide food sources to organisms growing in pelagic habitats. High numbers of heterotrophic bacteria and cyanobacteria are transported into the deep sea attached to rapidly sedimenting particles.
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Hence, there is every possibility of genetic exchange between populations previously assumed to be genetically isolated.
Most marine bacteria are gram negative and motile. For example, Pseudomonas, Vibrio are dominant genera followed by Flavobacterium, Alcaligenes and Microcystis. Actinomycetes are also found in marine waters. Some gram positive bacteria like Bacillus are found in marine sediments. Below the sediments, anaerobic bacteria are composed of the autochthonous microorganisms including Desulfovibrio and methanogenic bacteria. Chemolithotrophs include Nitrosomonas, Nitrosococcus, Nitrospira and Nitrobacter
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Fungal flora of the sea Yeast are more common, e.g. Torulopsis, Candida, Cryptococcus, Saccharomyces, Rhodosporidium.
Algal flora of the sea The algal flora usually belong to Chlorophyta, Phaeophyta, Rhodophyta, Cyanophyta.e.g. Sargassum, Fucus. Chlorophyta and Chrysophyta members are prominent among phytoplankton found in the upper regions of surface (0-50 m). Planktonic cyanobacteria are common forms, e.g. Trichodesmium. Occasional blooms of Pyrrophycophyta members are common in the oceans causing the 'red tides' (ocean becomes red brown in colour). The toxins produced by some of the dinoflagellates kill fishes and other marine animals.
Some of the dinoflagellates produce neurotoxins which accumulate in shell fishes that feed on them. When ingested by humans such tainted sea food can cause paralytic shell fish poisoning (PSP).
Protozoan flora of the sea They are important component of marine zooplankton. They can tolerate up to 10% NaCl concentration. They include flagellates, rhizopods and ciliates, e.g. Radiolaria, Acantharia. They occur in the deeper layers of the sea. Marine protozoa graze on bacteria, phytoplankton and smaller forms of zooplanktons. Grazing provides a critical link in the marine food web between Very small primary producers and the higher members of the marine food web.
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