Behavior ofPseudomonas fluorescens within the hydrodynamic boundary layers of surface microenvironments

Phase, darkfield, and computer-enhanced microscopy were used to observe the surface microenvironment of flow cells during bacterial colonization. Microbial behavior was consistent with the assumptions used previously to derive surface colonization kinetics and to calculate surface growth and attachment rates from cell number and distribution. Surface microcolonies consisted of closely packed cells. Each colony contained 2ⁿ cells, where n is the number of cell divisions following attachment. Initially, cells were freely motile while attached, performing circular looping movements within the plane of the solid-liquid interface. Subsequently, cells attached apically, maintained a fixed position on the surface, and rotated. This type of attachment was reversible and did not necessarily lead to the formation of microcolonies. Cells became irreversibly attached by progressing from apical to longitudinal attachment. Longitudinally attached cells increased in length, then divided, separated, moved apart laterally, and slid next to one another. This resulted in tight cell packing and permitted simultaneous growth and adherence. After approximately 4 generations, individual cells emigrated from developing microcolonies to recolonize the surface at new locations. Surface colonization byPseudomonas fluorescens can thus be subdivided into the following sequential colonization phases: motile attachment phase, reversible attachment phase, irreversible attachment phase, growth phase, and recolonization phase.     

Cost of tokking: the energetics of substrate communication in the tok-tok beetle,Psammodes striatus

Summary Psammodes striatus, the tok-tok beetle, communicates by substrate vibrations produced by tapping its abdomen on the ground. MaleP. striatus responded readily to computer-synthesized vibrations. Oxygen consumption rate ( ) of individual male beetles (n=3; mean mass 3.01 g) was continually recorded by computer before, during and after tapping communication with the computer, which also counted the beetle's replies. Standard of motionless beetles was also measured, during which time marked discontinuous ventilation was apparent. Since the relation between and tapping rate was linear, it was possible to estimate net cost of tapping (0.0279 l O₂ g^–1 tap^–1) and minimum cost of tapping (0.0286 l O₂ g^–1 tap^–1). Kinematic analysis of trains of taps showed constant intertap period (ca. 150 ms) and distinctive amplitude modulation. The efficiency of muscular movement inP. striatus is 23% of metabolic input, assuming no elastic storage. This figure will drop to ca. 5–10% if significant elastic storage takes place. Minimum cost of searching for a mate via pedestrian locomotion is 340 J kg^–1 m^–2, but drops to 33 J kg^–1 m^–2 for tapping communication. Similar energetic ratios may play a role in the early stages of the evolution of some communication systems.Abbreviation STT computer-synthetized tap train