SENSITIVITY TO SALTS AND ORGANIC COMPOUNDS OF SOIL BACTERIA ISOLATED ON DILUTED MEDIA

Abstract

Bacteria were isolated from soil on a 100-fold dilution of nutrient broth agar, a 10-fold dilution of alubumin yeast extract agar, or agar without additional nutrient. Their growth was severely suppressed by full strength nutrient broth but well supported by a 100-fold dilution of nutrient broth and these organisms were proposed to be called dilute nutrient broth (DNB) organisms.
One percent each of peptone and meat extract, and 1% or 2% casamino acids severely suppressed growth of most of them. Glycine, arginine, serine, or lysine (10mM), yeast extract (0.1%), nicotinic acid or thiamine (20μg/ml), and sodium succinate (20-50mM) inhibited growth of many organisms though sensitivity of each organism to organic compounds was of a great variety. They were also highly sensitive to NaCl and KCl. Growth inhibition of some isolates by serine was recovered by coexisting threonine, alanine, or leucine and valine. Inhibitive effect of serine was also influenced by NaCl, KCl, CaCl₂, or MgCl₂.