Logarithmic sensing in Bacillus subtilis aerotaxis

Aerotaxis, the directed migration along oxygen gradients, allows many microorganisms to locate favorable oxygen concentrations. Despite oxygen’s fundamental role for life, even key aspects of aerotaxis remain poorly understood. In Bacillus subtilis, for example, there is conflicting evidence of whether migration occurs to the maximal oxygen concentration available or to an optimal intermediate one, and how aerotaxis can be maintained over a broad range of conditions. Using precisely controlled oxygen gradients in a microfluidic device, spanning the full spectrum of conditions from quasi-anoxic to oxic (60 n mol/l–1 m mol/l), we resolved B. subtilis’ ‘oxygen preference conundrum’ by demonstrating consistent migration towards maximum oxygen concentrations (‘monotonic aerotaxis’). Surprisingly, the strength of aerotaxis was largely unchanged over three decades in oxygen concentration (131 n mol/l–196 μ mol/l). We discovered that in this range B. subtilis responds to the logarithm of the oxygen concentration gradient, a rescaling strategy called ‘log-sensing’ that affords organisms high sensitivity over a wide range of conditions. In these experiments, high-throughput single-cell imaging yielded the best signal-to-noise ratio of any microbial taxis study to date, enabling the robust identification of the first mathematical model for aerotaxis among a broad class of alternative models. The model passed the stringent test of predicting the transient aerotactic response despite being developed on steadystate data, and quantitatively captures both monotonic aerotaxis and log-sensing. Taken together, these results shed new light on the oxygen-seeking capabilities of B. subtilis and provide a blueprint for the quantitative investigation of the many other forms of microbial taxis

DIGITAL CAPTURE AND FABRICATION TOOLS FOR INTERPRETATION OF HISTORIC SITES

Historic sites and the narratives they produce can have a lasting impact on the community through public engagement and education. However, when these sites are neglected and lost over time, opportunities to engage the public with the history of these places is lost with them. The interpretation of heritage that has been lost or forgotten is an emerging trend in humanities studies. This trend, in combination with technological advancements in digital media and representation, presents an innovative opportunity for historic preservation professionals to create new paths for public engagement. This paper discusses applications of photogrammetry, 3D modeling, and digital fabrication in digitally reconstructing interpretive models of the Larz Anderson Estate (now Larz Anderson Park). This site has changed dramatically through its transition from a private estate to a public park and recreation area, with few remnants of the original estate remaining extant. The above stated use of digital strategies aims to create digital and physical models of the estate’s change over time, with the aim of interpreting the site's lost heritage for the public. Combining existing archival research and heritage documentation methods with these digital representation techniques tells the story of a place that no longer exists