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Growth experiments are typically undertaken in liquid media, in part because measuring the optical density of a liquid culture is straightforward. However, liquid cultures present a number of problems in microgravity. Most organisms that passed our screening did not grow well under anaerobic conditions, and thus required some sort of gas exchange with the surrounding air. On the 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 liquid will remain in place. We explored several unsuccessful approaches to 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 concluded  that we had chosen mutually exclusive the  design requirements; requirements were mutually exclusive;  either we could achievegood  containment for liquid cultures at the expense of aerobic conditions, or we could achievegood containment for  aerobic conditions at the expense of liquid culture. culture containment.  We chose the latter,and  so our plates were prepared with solid media. Solid media is not traditionally used for OD measurements, and so our results need to be interpreted differently from OD in liquid culture. Using clear agar to maximize transparency, we programed the plate reader to take OD measurements at nine different locations in each well, each 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. OD in liquid media is thought to correspond to scattering of light by individual cells, whereas our measure corresponds measurements correspond  to the number, diameter diameter,  and thickness of the  colonies. The intervals elapsed between occultations of the reading points decrease exponentially, and so the average OD across each well behaves very similarly to traditional observations of log-phase growth in liquid media. The data from the different plate readers (Tecan and Molecular Dynamics) was compared at 96 hours by plotting the OD600 values against each other. While the concordance was not perfect, there was a very strong relationship between the two machines which provided validation of the data from both Molecular Dynamics machines (earth (ground  and ISS). space).  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 inferred contamination of the _B. methylotrophicus_ and _M. oleivorans_ wells and therefore discarded those data. Some wells showed a mixed Sanger sequence, suggesting the presence of more than one organism in the well, while others gave a clear identification as a contaminating organism. 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).  In this experiment, _Bacillus safensis_ grew to a final density of ~60% higher in space than on the ground, with very little variation between replicates (Figure X). The genome sequence of this strain, _Bacillus safensis_ JPL-MERTA-8-2 has just been published \cite{26586895} and may contain clues as to why this strain behaved so differently in space.  It is perhaps no surprise that most built environment-associated bacteria behave very similarly on the ISS as on earth. After all, the ISS is a home and office of sorts, with environmental conditions very similar to a building on earth with the exception of gravity. The ISS is maintained at around 22 °C with a relative humidity of around 60%. Nor did Also,  this experiment didn't  provide enough time to study the adaptation of bacteria to the environment on board the ISS. A related project from our lab has examined the microbial community already present on the ISS (Lang et al 2015). Given that the ISS appears to harbor similar microbes to built environments on earth, we also asked if there were close relatives to our 48 bacteria already present on the ISS. The vast majority (39/48) of our bacterial species were found in the existing microbial community data which is not surprising given the built environment origins of the isolates. This suggests that our data showing these species growing with similar kinetics on space and on earth is potentially relevant to the biology of the microbial communities already present on the ISS.