Effects of nutrient concentration on the growth of soil bacteria

Abstract

Bacteria isolated from soil were cultivated on conventional nutrient broth at various dilutions (NB, NB/10, NB/100, NB/1,000, and NB/10,000). Based on the results obtained these organisms were divided into four groups by the range of dilution of the full strength nutrient broth (NB) on which growth was recognized; those which showed appreciable growth only on media within a range from NB to NB/1,000 were referred to as type I and those which grew well on media of a range involving further dilutions of NB, to type II. Among the isolates which did not grow well on NB, those which grew only on media within a range from NB/10 to NB/1,000 were assigned to type III, and those which grew well on media of a range involving further dilutions, to type IV. Some isolates of types II and IV showed appreciable growth even in distilled water. They were considered to have an ability of utilizing very small amounts of substances in liquid or air. In connection with these results we discussed the criteria for the identification of oligotrophs.