Astropharmacy / Biotechnology

Ultrastructure of Serratia liquefaciens Grown at 7 mbar Under Simulated Martian Conditions

By Keith Cowing
Microorganisms via PubMed
December 8, 2025
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Ultrastructure of Serratia liquefaciens Grown at 7 mbar Under Simulated Martian Conditions
Transmission electron micrographs of Serratia liquefaciens cell walls grown under lab-standard (24 h) and Mars low-PTA conditions (28 d) (see text). (A) Cell walls of S. liquefaciens cells grown under lab-standard conditions measured on average 29.4 µm thick as measured from the inside of the periplasmic layer and ending at the outside of the outer membrane (i.e., similar to Gram-negative cell walls described by Hobot [21]). (B) In contrast, cell walls were significantly thinner in S. liquefaciens when grown under Mars low-PTA conditions and measured approx. 24.3 µm. The cell-wall thicknesses of the other Earth controls incubated for 28 d at low temperatures fell between the two extremes given above (see Table 1). Scale bars are present in the lower left corners of all images. [Magnifications: (A) = 1600×; (B) = 1100×]. — Microorganisms

Cells of Serratia liquefaciens were grown on trypticase soy agar (TSA) for 28 d under Martian conditions of 7 mbar, 0°C, and CO2-enriched anoxic atmospheres (called Mars low-PTA conditions).

Earth controls were maintained for 24 h at 1013 mbar, 30°C, and a standard pN2/pO2 gas composition. Cells were harvested at either 24 h or 28 d from TSA surfaces and processed for SEM and TEM imaging.

Cells of S. liquefaciens grown under Earth conditions were uniform in shape and size, averaging approximately 1.25 µm in length and 0.5 µm in width. Fimbriae were observed on 10–20% of cells grown under Earth conditions.

Key features of low-PTA grown cultures were (1) cells exhibited swollen blunt ends at sites of cell division tapering to unusually constricted points on the distal ends of progeny cells, (2) cell division appeared disrupted with division planes occurring at odd angles often forming right-angle oriented daughter cells, (3) some cells failed to form divisional planes resulting in long spiral and oddly shaped cells measuring up to 6–8 µm in length, and (4) fimbriae were lacking. Cell walls were found to be approx. 17% thinner when cells were grown in low-PTA environments compared to lab-standard conditions.

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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