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This article in SSSAJ

  1. Vol. 62 No. 3, p. 663-670
     
    Received: July 31, 1997


    * Corresponding author(s): mmorra@uidaho.edu
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doi:10.2136/sssaj1998.03615995006200030017x

Survival of Pseudomonas fluorescens 2-79RN10 in Clay Powders Undergoing Drying

  1. Matthew J. Morra ,
  2. Martha H. Chaverra,
  3. Louise-Marie Dandurand and
  4. Cindy S. Orser
  1. Soil Science Division, Univ. of Idaho, Moscow, ID 83844-2339

Abstract

Abstract

Although clay minerals differentially alter bacterial survival during desiccation, the mechanism responsible is speculative. Our objective was to determine how clay water content might control the enhanced survival of Pseudomonas fluorescens (Migula) 2-79RN10 in the presence of various clays. Pseudomonas fluorescens 2-79RN10 was suspended in phosphate buffer, mixed into Ca2+-saturated pyrophyllite, kaolinite, clinoptilolite, and montmorillonite (0.5 mL of cell suspension g−1 clay), and air dried at 20°C. Bacterial colony-forming units (CFU), gravimetric water, and water activity (aw) were determined when mixed and at 9, 14, 19, 28, and 48 h after mixing. Bacterial survival was greatest in air-dried montmorillonite and lowest in kaolinite. The rate of change in aw, final aw values, and rate of gravimetric water loss were similar for all clays. However, aw values during the initial stage of drying varied because the same cell-suspension volume was amended to equivalent weights of clays possessing different surface areas. The length of time prior to decreases in aw varied in the order: kaolinite > clinoptilolite > pyrophyllite > montmorillonite, a sequence inversely proportional to survival. Alteration of clay particle size and amendment with different cell-suspension volumes showed that increased bacterial survival could be achieved by shortening the time aw remained elevated. Increased survival of 2-79RN10 is thus promoted by cell-clay interactions resulting from more rapid decreases in aw values during the initial stages of drying. Our results have relevance to bacterial survival in clay formulations and soil.

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