The influence of pH on the growth rate and viability of neutrophilic and acidophilic streptomycetes.

The influence of pH on the specific growth rates of two acidophilic and two neutrophilic soil streptomycetes was studied. The acidophiles had maximum growth rates over a broad range from pH 4.5 to 5.5, while the neutrophiles had clearly defined optima at pH 7.0. Mycelium of neutrophiles was less tolerant of acidity than that of acidophiles; both showed decreased viability at pH levels below those which allowed growth. Spores of neutrophiles and acidophiles were equally tolerant of acidity and this may allow the former to survive in acid soils. Both spores and mycelium of acidophiles remained viable at pH levels above those allowing growth.