THE EFFECT OF YEAST EXTRACT AND CASITONE ON THE RESPONSE TO SALT OF THE MICROFLORA OF A HIGHLY SALINE SOIL

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Abstract
Salt-dependent, salt-resistant, and salt-sensitive bacteria were found at depths of 0–50 cm in a hydrohalomorphic soil near the shore of the Red Sea. Highest counts were obtained on soil-extract agar supplemented with 5% sodium chloride, 0.02% yeast extract, and 0.04% Casitone. Most of the bacteria, upon initial isolation, failed to grow on counting media containing 5% or 10% sodium chloride unless yeast extract and Casitone were present. However, all isolates, randomly selected from the counting medium containing 10% sodium chloride and supplemented with yeast extract and Casitone, did not need these supplements when transferred onto a new medium of the same salt concentration.Bacterial counts were significantly affected by the salt concentration of both the diluting solution and the growth media. It was concluded that the addition of yeast extract and Casitone to the growth media resulted in a partial recovery and protection of the cells from damage occurring during the initial dilution and plating procedure.