Buoyancy-Driven Fluid Flow Generated by Bacterial Metabolism and its Proposed Relationship to Increased Bacterial Growth in Space
and held by
Previous investigations have reported that bacterial growth increases in space flight; however, the underlying physical mechanisms responsible for these changes have not been fully determined. As bacteria consume nutrients, they excrete by-products whose presence can influence the onset of exponential growth and affect final cell population density. It is assumed that these metabolic processes create a reduced-density fluid zone and/or a solute gradient around each cell. On Earth, this density difference may result in local buoyancy-driven convection of the excreted by-products. The absence of convection and sedimentation in the low-gravity space flight environment, however, can be expected to alter the fluid dynamics surrounding the cells by limiting transport to diffusion only. Based on this biophysical model, it was hypothesized that acceleration affects the lag phase duration and final cell concentration of suspended bacterial cultures in a predictable, non-linear manner, due to the resultant changes incurred in the extracellular fluid composition. Eight experiments at various levels of acceleration consistently supported this hypothesis, resulting in predictable growth kinetics. In additional experiments, macroscopic plumes of fluid were observed and analyzed rising from metabolizing bacterial cultures. If similar fluid dynamics were found to occur on a microscopic level, it would help explain how acceleration affects bacterial growth kinetics.