The influence of pH on starch hydrolysis by neutrophilic and acidophilic streptomycetes.

The effect of pH on the starch hydrolysing activity of one neutrophilic and two acidophilic soil streptomycetes was studied in detail. The neutrophilic culture extract was active from pH 5.0 to pH 8.0, with optimum activity from pH 5.5 to 6.5. Acidophile activity occurred from pH 2.5 to 7.0 with an optimum at pH 4.0 to 4.5. After storage for 24 h at different pH levels, neutrophiles showed a sharp reduction in activity at pH 5.0 with none below this point; some activity was maintained up to pH 10.0. Acidophiles remained active after storage at pH 3.0 and retained some activity up to pH 7,0--9.0. Less detailed tests on a range of soil streptomycetes showed that the differences between acidophiles and neutrophiles were consistent. The results indicated that acidophilic streptomycetes may produce a range of exo-enzymes which are themselves acid-requiring and play an important part in decomposition processes in acidic soils and litters.