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BACTERIAL BIOFILMS UNDER MICROGRAVITY CONDITIONS.  P.W. Baker and L. Leff.  Dept. of Biological Sciences, Kent State Univ., Kent, OH 44242.

   Bacteria and other microorganisms commonly form communities embedded in an extracellular polysaccharide matrix on surfaces (i.e., biofilms) exposed to water.  The purpose of this study was to examine the formation of bacterial biofilms under simulated microgravity conditions using a modified rotary cell culture system (RCCS).  The results obtained were compared to biofilms formed under normal gravity conditions.  Three types of bacteria were used in the experiments, Xanthomonas maltophila, Sphingobacterium thalpophilium and Burkholderia picketti, that were originally isolated either from condensated water (hot or cold) or the SVO storage tank from the Mir space station.  Prior to the experiments, the bacteria were grown under nutrient limited conditions and incubated under low nutrient conditions during the experiments.  Biofilms were formed on round stainless steel disks held within the RCCS that were periodically removed and sampled.  Planktonic cells were also sampled.  Cell numbers were determined using several different methods that revealed cell number and physiological state.  Methods of enumeration used included: colony forming units (CFU), the BacLight Live-Dead stain (Molecular Probes), DAPI and 16S rRNA fluorescent in situ hybridization.  Different methods of enumeration yielded different results as the number and activity of the cells changed.  There were also differences among the three species examined.  Initial results suggest that there were subtle differences between planktonic cells grown under microgravity conditions compared to gravity conditions.  Under microgravity conditions, the bacteria appeared to have difficulty attaching to the metal disks used as the biofilm substrate as cell numbers were low; however, these disks were readily colonized under other experimental conditions. In conclusion, the bacteria studied have the ability to persist under low nutrient conditions and differed in their responses to starvation and gravitational conditions.   This research was supported by a grant from NASA.

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