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- All Subjects: Microbiology
- Creators: Barrila, Jennifer
- Creators: Nickerson, Cheryl
One of the identified health risk areas for human spaceflight is infectious disease, particularly involving environmental microorganisms already found on the International Space Station (ISS). In particular, bacteria belonging to the Burkholderia cepacia complex (Bcc) which can cause human disease in those who are immunocompromised, have been identified in the ISS water supply. This present study characterized the effect of spaceflight analog culture conditions on Bcc to certain physiological stresses (acid and thermal as well as intracellular survival in U927 human macrophage cells). The NASA-designed Rotating Wall Vessel (RWV) bioreactor was used as the spaceflight analogue culture system in these studies to grow Bcc bacterial cells under Low Shear Modeled Microgravity (LSMMG) conditions. Results show that LSMMG culture increased the resistance of Bcc to both acid and thermal stressors, but did not alter phagocytic uptake in 2-D monolayers of human monocytes.
Antibacterial susceptibility testing reveals that hydrated clays containing pyrite and I-S are effective at killing (100%) of the model pathogens tested (E. coli and S. epidermidis) when pH (< 4.2) and Eh (> 450 mV) promote pyrite oxidation and mineral dissolution, releasing > 1 mM concentrations of Fe2+, Fe3+ and Al3+. However, certain oxidized clay zones containing no pyrite still inhibited bacterial growth. These clays buffered solutions to low pH (< 4.7) and oxidizing Eh (> 400 mV) conditions, releasing lower amounts (< 1 mM) of Fe and Al. The presence of carbonate in the clays eliminated antibacterial activity due to increases in pH, which lower pyrite oxidation and mineral dissolution rates.
The antibacterial mechanism of these natural clays was explored using metal toxicity and genetic assays, along with advanced bioimaging techniques. Antibacterial clays provide a continuous reservoir of Fe2+, Fe3+ and Al3+ that synergistically attack pathogens while generating hydrogen peroxide (H2O¬2). Results show that dissolved Fe2+ and Al3+ are adsorbed to bacterial envelopes, causing protein misfolding and oxidation in the outer membrane. Only Fe2+ is taken up by the cells, generating oxidative stress that damages DNA and proteins. Excess Fe2+ oxidizes inside the cell and precipitates Fe3+-oxides, marking the sites of hydroxyl radical (•OH) generation. Recognition of this novel geochemical antibacterial process should inform designs of new mineral based antibacterial agents and could provide a new economic industry for such clays.