Attachment to Autoclaved Soil of Bacterial Cells from Pure Cultures of Soil Isolates

Pure cultures of Arthrobacter globiformis and four fresh soil isolates were incubated individually in autoclaved soil, in both the presence and absence of glucose. These bacteria grew in the soil and, except for A. globiformis, eventually attached firmly to the soil solids. Firmly attached cells were defined as those which could not be separated from the soil solids by blending combined with a series of low-speed centrifugal washings. The attachment attained by the soil isolates appeared to duplicate that of the overall bacterial population that resides naturally in unaltered, unamended soil. Cell attachment in the autoclaved-soil system was accelerated slightly by glucose, but, except for one soil isolate, several months of incubation were still required before firm attachment was complete. Electron microscopy indicated that all attached cells produced extracellular polysaccharide slimes in the autoclaved soil and that these materials appeared to connect the cells to surrounding pieces of soil debris. The actual role of polysaccharides in attachment was not clear, however, because at least one of these organisms possessed extracellular slime during the long period in which it had not yet attached to the soil.