Identification of soil micro‐habitats for growth, death and survival of a bacterium, γ‐1,2,3,4,5,6‐hexachlorocyclohexane‐assimilating Sphingomonas paucimobilis, by fractionation of soil

Abstract

Abstract A soil bacterium, Sphingomonas paucimobilis, is known to be the only bacterium which can aerobically assimilate γ‐1,2,3,4,5,6‐hexachlorocyclohexane (γ‐HCH). Indigenous γ‐HCH‐assimilating S. paucimobilis survives in the soil where γ‐HCH has been annually applied since 1973. In contrast, γ‐HCH‐assimilating S. paucimobilis strain SS86 cannot survive when inoculated into the control soil, although it can multiply in the presence of γ‐HCH. Micro‐habitats of γ‐HCH‐assimilating S. paucimobilis indigenous or inoculated into the soils were identified by fractionation of the soils. When γ‐HCH was added to the soil, indigenous γ‐HCH‐assimilating S. paucimobilis grew. Most of the growing indigenous bacteria were found in fractions smaller than 0.025 mm which corresponded to soil inter‐aggregate pores, and died afterwards. However, the indegenous bacteria which survived for a long period were found mainly in fractions larger than 0.025 mm which contained soil aggregates. When γ‐HCH‐assimilating strain SS86 was inoculated, the bacteria were located in inter‐aggregate pores and died quickly. Consequently, association of the bacteria with soil aggregates was suggested to be related to the long‐term survival of γ‐HCH‐assimilating S. paucimobilis. Copyright © 1992, Wiley Blackwell. All rights reserved