Photosensory and chemosensory motility responses in both gliding and swimming bacteria (phototrophic and chemotrophic types) are regarded as primitive "neurosensory" analogs and are presumed to be adaptations that enhance the survival potential of the organism in nature. In this proposal, diel vertical migration patterns of microorganisms will be examined in a variety of microbial mat communities representing highly advantageous strategies that optimize both the day and night microenvironments. The objective will be to: quantify the diel schedule of movements in hot spring and other mats; to experimentally determine the physical and chemical cues to which organisms respond; and to assess survival rate or comparative growth when migration patterns or microenvironments are altered. The vertical up/down migrations over a 24 hr period occur over short distances (a few mm) that represent sharp gradients in light intensity, oxygen tension, sulfide concentration, and other chemical factors. The results will place tactic behavior in the context of the natural habitat, previously undetermined in ecological studies and will provide data for understanding the "selective forces" involved in the evolution of oriented motility in microorganisms.
