Figure 6.

Exposure of four spacecraft strains to low-PTA conditions on different medium types. The four species were Staphylococcus equorum subsp. equorum, Acinetobacter johnsonii, Sphingomonas yunnanensis, and Bacillus simplex. The media tested were TSA + vitamins, TSA + sulfate, and TSA + Fe³⁺ at pH 7, in which plates were incubated at low-PTA conditions for up to 28 days. Samples were taken every 7 days. Cells were applied on agar plates as 2.5-µL drops (~ 2.5 × 10⁵ cells/drop), squares of agar/cells were cut out, and subsequent MPN assays completed. The data are reported as log 10 (N/N₀) in which N₀ = viable cell number on at T = 0 time, and N = viable cell numbers at specific points after incubation from 7 to 28 days (n = 6; error bars are standard deviations).