## 3 Results
### Yeast Growth
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample** & **Flight-Generation Time (min)** & **Ground-Generation Time (min)** \\ \hline FPA-Early Low (Micro-6) & 155 & 159 \\ FPA-Early High (Micro-6) & 303 & 303 \\ FPA-Late Low (Micro-6) & 163 & 163 \\ FPA-Late High (Micro-6) & 300 & 310 \\ FPA-Low (Micro-14/FPA) & 113 & 129 \\ FPA-High (Micro-14/FPA) & 127 & 126 \\ FEP-Large (Micro-14/FEP) & 95 & 99 \\ FEP-Small (Micro-14/FEP) & 113 & 118 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Generation time of yeast cells cultured in spaceflight and terrestrial control bioreactors. Figure 3: Cell growth determination using direct cell counts at the end of each of the three missions. Cell growth was evaluated in the (**A**) Micro-6 (FPA), (**B**) Micro-14/FPA, and (**C**) Micro-14/FEP payloads. These analyses allowed mission-to-mission comparison using the same hardware (FPA comparison between **A,B**), as well as comparison using two different types of spaceflight hardware (**A**/**B** = FPAs versus **C** = FEP bags). ’Low’ refers to the samples seeded with a low inoculum, ’High’ refers to samples seeded with a high inoculum, ’Early’ refers to samples activated near the beginning of the spaceflight mission, ’Late’ refers to samples activated late in the spaceflight mission, and ’viable’ refers to samples returned alive. Differential growth was not noted in the viable samples since flight cells were subjected to different transport temperatures than the terrestrial controls. Large FEP bags represent those with a final volume of 12 mL; small FEP bags represent those with a final volume of 3 mL. Black bars = flight; green bars = terrestrial controls. * \(p\) = 0.02; ** \(p\) = 0.01. In the Micro-14 experiments, yeast grew to a 10-fold higher cell density than in the Micro-6 payload, even though they both used the FPA hardware (Table 2, Figure 3B). As indicated in Table 2, the generation times were similar among the Micro-14/FPAs, regardless of the initial cell concentration. Due to the similarity in growth characteristics of the Low and High inoculum samples in the Micro-14/FPA payload, the data were aggregated for Figure 3B. In this case, there is a trend toward an increased cell density of cells cultivated in microgravity. Finally, yeast cells grew _most robustly_ when cultured in the FEP bag bioreactor (Table 2, Figure 3C) both in terms of shortest generation times and highest cell density. Indeed, the cell density observed in the FEP bags resembles that obtained with ground-based shaker cultures (2-3 \(\times\) 10\({}^{8}\) cells/mL). For comparison, activation occurred at approximately 4100 cells/mL in the Large FEP bags (parent cultures for the serial cultivation) and approximately 33,300 cells/mL in the Small FEP bags (medium-only control bags from the antifungal drug study). These inoculations were the result of serial dilutions and inoculation done by flight crew (and corresponding ground crew), so cell concentrations are predicted. The cells within the Large FEP bags likely did not reach maximal density due to the length of the growth period, which in hindsight could have been extended another couple of hours. Data obtained from the small FEP bags in this payload indicates that _C. albicans_ grows to a higher density in microgravity than in the terrestrial controls (** \(p\) = 0.01). Cumulatively, there was a trend in each of the payloads and in two types of hardware suggesting yeast grows to a higher cell density in microgravity than in terrestrial control conditions.