Fathi Karouia

Transient gene and microRNA expression profile changes of confluent human fibroblast cells in spaceflight

Microgravity, or an altered gravity environment different from the 1 g of the Earth, has been shown to influence global gene expression patterns and protein levels in cultured cells. However, most of the reported studies that have been conducted in space or by using simulated microgravity on the ground have focused on the growth or differentiation of these cells. It has not been specifically addressed whether nonproliferating cultured cells will sense the presence of microgravity in space. In an experiment conducted onboard the International Space Station, confluent human fibroblast cells were fixed after being cultured in space for 3 and 14 d, respectively, to investigate changes in gene and microRNA (miRNA) expression profiles in these cells. Results of the experiment showed that on d 3, both the flown and ground cells were still proliferating slowly, as measured by the percentage of Ki‐67+ cells. Gene and miRNA expression data indicated activation of NF‐kB and other growth‐related pathways that involve hepatocyte growth factor and VEGF as well as the down‐regulation of the Let‐7 miRNA family. On d 14, when the cells were mostly nonproliferating, the gene and miRNA expression profile of the flight sample was indistinguishable from that of the ground sample. Comparison of gene and miRNA expressions in the d 3 samples, with respect to d 14, revealed that most of the changes observed on d 3 were related to cell growth for both the flown and ground cells. Analysis of cytoskeletal changes via immunohistochemistry staining of the cells with antibodies for α‐tubulin and fibronectin showed no difference between the flown and ground samples. Taken together, our study suggests that in true nondividing human fibroblast cells in culture, microgravity experienced in space has little effect on gene and miRNA expression profiles.—Zhang, Y., Lu, T., Wong, M., Wang, X., Stodieck, L., Karouia, F., Story, M., Wu, H. Transient gene and microRNA expression profile changes of confluent human fibroblast cells in spaceflight. FASEB J. 30, 2211–2224 (2016). www.fasebj.org

MICROORGANISMS, ORGANIC CARBON, AND THEIR RELATIONSHIP WITH OXIDANT ACTIVITY IN HYPER-ARID MARS-LIKE SOILS: IMPLICATIONS FOR SOIL HABITABILITY

Abstract Soil samples from the hyper-arid region in the Atacama Desert in Southern Peru (La Joya Desert) were analyzed for total and labile organic carbon (TOC and LOC), phospholipid fatty acids (PLFA), quantitative real time polymerase chain reaction (qRT-PCR), 4′,6-diamidino-2-phenylindole (DAPI)-fluorescent microscopy, culturable microorganisms, and oxidant activity, to understand the relationship between the presence of organic matter and microorganisms in these types of soils. TOC content levels were similar to the labile pool of carbon suggesting the absence of recalcitrant carbon in these soils. LOC ranged between 2 to 60 µg/g of soil. PLFA analysis indicated a maximum of 2.3 × 105 cell equivalents/g. Culturing of soil extracts yielded 1.1 × 102–3.7 × 103 CFU/g. qRT-PCR showed between 1.0 × 102 and 8 × 103 cells/g; and DAPI fluorescent staining indicated bacteria counts up to 5 × 104 cells/g. Arid and semiarid samples (controls) showed values between 107 and 1011 cells/g with all of the methods used. Importantly, the concentration of microorganisms in hyper-arid soils did not show any correlation with the organic carbon content; however, there was a significant dependence on the oxidant activity present in these soil samples evaluated as the capacity to decompose sodium formate in 10 hours. We suggest that the analysis of oxidant activity could be a useful indicator of the microbial habitability in hyper-arid soils, obviating the need to measure water activity over time. This approach could be useful in astrobiological studies on other worlds.

Long-term exposure of bacterial cells to simulated microgravity

Previous space flight experience has demonstrated that microorganisms are just as ubiquitous in space habitats as they are on Earth. Numerous incidences of biofilm formation within space habitats have been reported; some of which were identified only after damage to spacecraft structures and irritation to astronaut’s skin occurred. As we increase the duration of spaceflight missions, it becomes legitimate to question the long-term effects of microgravity on bacteria. To begin this assessment, Escherichia coli K-12 strain MG1655 was grown for one thousand generations (1000G) under low shear modeled microgravity. Subsequently, growth kinetics and the presence of biofilm were assessed in the 1000G strain as compared to a strain (1G) briefly exposed to LSMMG. Overall, the analysis revealed that (i) there was no obvious difference in growth kinetics between the 1G and 1000G strains, and (ii) although biofilm formation was not seen in the 1G strain it did in fact occur as exposure time increased. The results suggest that long-term exposure to the space environment likely favors biofilm formation in many organisms.