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**Results and Discussion**  Growth experiments are typically undertaken in liquid media, in part because measuring the optical density of a liquid culture is straightforward. However, liquids liquid cultures  present a number of problems in microgravity including the risk of escaping from containment microgravity. Most organisms that passed our screening did not grow well under anaerobic conditions,  and thus required some sort of gas exchange with  the fact that if any air were in surrounding air. On  the tube ground, aerobic conditions are easily created by incubating in open or loosely capped vessels. This is impractical and unsafe in microgravity; there is no "safe" orientation in which  the culture media would form floating blobs. After extensive effort we were unable liquid will remain in place. We explored several unsuccessful approaches  to design a this problem. For example, we found that gas-permeable  plate seals leak when inverted, and their adhesion failed completely after freezing. We also fabricated custom plates with seals made from hydrophobic PDMS with micron-diameter vent holes, but these also leaked slightly when inverted.   We eventually came to the conclusion  that we had chosen mutually exclusive design requirements; either we  could safely contain achieve good containment for liquid  cultures while both allowing accurate OD measurements and permitting at  the passage expense  of oxygen. Therefore aerobic conditions, or  we turned to could achieve good containment for aerobic conditions at the expense of liquid culture. We chose the latter, and so our plates were prepared with  solid media. Solid  mediawhich  is not traditionally used for OD measurements. A measurements, and so our results need to be interpreted slightly differently from OD in liquid culture. Using  clear agarallows penetration of light and if measurements are taken throughout the well it is possible  to extrapolate growth as the bacteria intersect each measurement point. Therefore maximize transparency, we programed  the plate reader to take  OD values shown represent the average of measurements at  nine different  locations throughout in  each well,with  each measurement repeated 25 of which was measured twenty five  times per observation. The plates were inoculated in a manner intended to create many small colonies (see Materials and Methods). As these colonies grow, their edges intersect with reading points, and the OD for that point increases in a stepwise fashion. As the colony thickens, the OD gradually increases. The intervals elapsed between these occultations of reading points decrease exponentially, and so the average OD across each well behaves very similarly to traditional observations of log-phase growth  in succession. liquid media.  By this measure, the vast majority of the bacteria (45/48) behaved very similarly in space and on earth (Table 1, Figure X). Only three bacteria showed a significant difference in the two conditions; _Bacillus safensis_, _Bacillus methylotrophicus_, and _Microbacterium oleivorans_. However, upon Sanger sequencing the 16S rRNA gene from cultures obtained from the wells on the space plates and the ground plates, we observed contamination of the _B. methylotrophicus_ and _M. oleivorans_ wells and therefore discarded those data. The remaining candidate was _Bacillus safensis_, collected at the Jet Propulsion Laboratory (JPL-NASA) on a Mars Exploration Rover before launch in 2004. As part of standard Planetary Protection protocols, all surface-bound spacecraft are sampled during the assembly process and those strains are then saved for further analysis. We obtained this strain as part of a collection of JPL-NASA strains to send to the ISS (Table 1).