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AEROTAXIS IN A CALCIFYING ALGA DOES NOT REQUIRE PHOTOSYNTHESIS. J. Duke¹, C. Auzenne³ and M. Marsh². ¹Dept. of Orthodontics, Dental Branch, ³Dept. of Biochemistry and Molecular Biology, Medical School, University of Texas Health Science Center at Houston, ³DeBakey High School for the Health Professions, Houston.

   Previously, we determined that the calcifying alga Pleurochrysis cartarae is aerotaxic during the light portion of the light-dark cycle. The relationship between locomotion and photosynthesis led us to the objective of our current experiment, to determine if aerotaxis occurs in the dark as well. Four experimental devices were constructed using 35 ml T-flasks and Silastic “bubbles” from the 1992 CELLS experiment on IML-1 (Duke and Montufar-Solis, 1999, Adv. Space Res.).   The two part bubble was halved and one-half (one bubble) inserted into a hole made in the side of the T-flask, then sealed into place with Silastic glue.  Flasks were cured for a week and rinsed extensively prior to use.  Cells from a stock cell culture of P. carterae,  Plymouth strain 136,  were grown overnight in F/2 medium (18^oC), then divided into the 4 T-flasks and placed in the incubator.  Movement of gases through the membranes was confirmed by appearance of gas bubbles in the flask.  Aerotaxis in the light was positive in 3 of 4 flasks as assessed by the accumulation of cells at a particular distance from the gas exchange bubble, forming a graded green arc around a clear zone next to the bubble. Cells were dark adapted for 48 hrs, then placed in the experimental containers and  checked for the presence of a gradient every 10 minutes. After 10 minutes, a gradient had been established in 2 of the 4, and by 30 minutes in 3 of the 4. Over the hour of observation, the gradient did not disperse, and no gravity-related bioconvection was observed in dark cultures. The experiment was repeated with the same result and with the same flask not demonstrating aerotaxis. This we attributed to limited gas exchange due to age-related cross-linking of the membrane polymer.  This study shows that photosynthesis is not necessary for aerotaxis to occur in P. carterae cultures, and demonstrates how air bubbles in solutions in spaceflight experiments could alter results of gravitaxis experiments.  Support:  Michael E. DeBakey High School for the Heath Professions; Dept of Orthodontics, UT Dental Branch.