Ecology of Microorganisms in Saline Waters (Seas and Oceans)

Abstract

The waters of the seas and oceans of the world contain large amounts of solutes; mainly, salt of about 3.5 g/L, occupy about 71% of the earth’s surface and have an average depth of 3.8 km. The photic zone of seas and oceans, about 200 m deep, is the region permeated by sunlight where photosynthesis can take place. It has the greatest biodiversity, and all food for the marine population arises from the photic zone; such food includes marine snow which consists of globules of mucopolyssacharides containing dead and living microorganisms floating downward toward the deep ocean. Marine organisms are adapted to the unique conditions found in the marine open sea (pelagic zone) environment: high salinity (3.5 g/L), low temperature (about 4°C), and high barometric pressure of up to 500 bar depending on the depth. Thermophilic organisms grow near the occasional hot thermal vents where hot magma spews out onto the ocean floor.

Using the technique of 16S rRNA, it has been found that over 70% of marine bacteria have not been cultured and hence have no counterparts among known bacteria. Microscopic cyanobacteria (picophytoplankton) make up 15% of all the bacteria. Among them, Synechoccus and Prochlorococcus, predominate and constitute the most abundant photosynthetic microbes on earth, contributing more than 50% of the total marine photosynthesis. Of the cultivated bacteria, Roseobacter spp. form about 15% of the total bacteria, while green non sulfur bacteria make up about 6%.