HR: 0800h
AN: B41A-0029    [Abstracts]
TI: Linear Chain Formation by Unicellular Bacteria During Mat Growth Under Low-Energy Flows
AU: * Tice, M M
EM: tice@geo.tamu.edu
AF: Department of Geology & Geophysics, TAMU 3115, Texas A&M University, College Station, TX 77843-3115, United States
AU: Newman, D K
EM: dkn@mit.edu
AF: Departments of Earth, Atmospheric & Planetary Sciences and Biology, 77 Massachusetts Ave., Massachusetts Institute of Technology, Cambridge, MA 02139, United States
AU: Grotzinger, J P
EM: grotz@gps.caltech.edu
AF: Division of Geological & Planetary Sciences, California Institute of Technology, 1200 E. California Blvd., Pasadena, CA 91125, United States
AB: Biofilm morphologies and material properties are known to be functions of overlying fluid flow strength. It has been hypothesized that microbial mats and stromatolites also respond morphologically to fluid flow. We show that microscopic textures of experimentally grown mats of the unicellular cyanobacterium Synechocystis sp. PCC 6803 respond sensitively to overlying flow. Cultures were grown in two chemostats in which growth medium was replaced at a rate much faster than the bacteria's instantaneous growth rate, thus selecting for individuals attached to surfaces. Small petri dishes at the bottoms of each chemostat received innocula at the beginning of the experiment. One chemostat was stirred at a low rate such that there was no measurable flow across the tops of the dishes, while the other was stirred at a rate maintaining a flow of approximately 0.7 cm/s at 1 cm over the dishes. Cultures were grown for 10 days during which thick biofilms/mats developed in the dishes. In addition to biofilms developed on the petri dish surfaces, cultures in the rapidly stirred chemostat developed thick "streamers" which projected up into and were deflected by the overlying flow. Samples were collected from films and, in the rapidly stirred chemostat, from streamers by pipetting and by pinching between two thin bamboo sticks. Samples were examined by fluorescence microscopy with a 40x objective. Without fluid flow, cells were only loosely associated and showed little or no spatial organization. Under the modest flow set up in the rapidly stirred chemostat, cells in both biofilms and streamers formed long linear chains arranged in sheets or tight bundles. These results suggest that hydraulic factors may be significant in shaping mat textures at the scale of 10-100 μm by modifying the spatial associations of groups of cells. If preserved in microcrystalline quartz or carbonate, the chains formed in these experiments could be mistaken for filamentous bacteria. Care must be taken when inferring microfossil morphology in moderately preserved mat samples, particularly in sediments deposited under low-energy currents.
DE: 0406 Astrobiology and extraterrestrial materials
DE: 0444 Evolutionary geobiology
DE: 0448 Geomicrobiology
SC: Biogeosciences [B]
MN: 2007 Fall Meeting