Effect of heptachlor on numbers of bacteria,actinomycetes and fungi in soil

Growth of many soil microorganisms was inhibited on culture media containing heptachlor. At a concentration of 25 mg/l., heptachlor killed 63 per cent of the bacteria transferred from soil dilution plates. Heptachlor, at 100 mg/1. in agar media used for isolating microorganisms from soil, prevented the development of 89 per cent of the bacteria, 81 per cent of the actinomycetes, and 50 per cent of the fungi that appeared on isolation plates without heptachlor. After heptachlor was added to soil, fungal populations declined and bacterial populations increased. Numbers of bacteria were related to amount of heptachlor added; higher concentrations of heptachlor in soil resulted in larger populations. A selective increase in numbers of fungi which would grow on media containing heptachlor at 100 mg/l. occurred in soils amended with heptachlor in amounts ordinarily used in field practices, but a similar increase of heptachlor-resistant bacteria occurred only in soils amended with higher amounts of heptachlor.