Background/Aims: In a variety of investigations described in the literature it was not clear to what extent the transmembrane potential red blood cells (RBCs) was changed after the cells have been transferred into low ionic strength (LIS) solutions. Another open question was to find out how fast the transmembrane potential of RBCs in LIS solution will change and which final new equilibrium value will be reached. Methods: The transmembrane potential of human and bovine RBCs was investigated using the potential-sensitive fluorescent dye DIBAC₄(3) (bis(1,3-dibutylbarbituric acid) trimethine oxonol) as well as the CCCP (carbonylcyanide-m-chlorophenylhydrazone) method. Results: Under physiological conditions the transmembrane potential was about -10 mV in agreement with literature data. However, when the RBCs were transferred into an isosmotic low ionic strength medium containing sucrose the transmembrane potential increased to +73 mV and +81 mV for human and bovine RBCs, respectively. In case of human RBCs it continuously decreased reaching finally an equilibrium state of -10 mV again after 30 - 60 min. For bovine RBCs the transmembrane potential declined more slowly reaching a value of +72 mV after 30 min. Conclusions: Investigations of parameters of RBCs depending on transmembrane potential cannot be performed with human RBCs in LIS media.

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Microbial biofilms can lead to persistent infections and degrade a variety of materials, and they are notorious for their persistence and resistance to eradication. During long-duration space missions, microbial biofilms present a danger to crew health and spacecraft integrity. The use of antimicrobial surfaces provides an alternative strategy for inhibiting microbial growth and biofilm formation to conventional cleaning procedures and the use of disinfectants. Antimicrobial surfaces contain organic or inorganic compounds, such as antimicrobial peptides or copper and silver, that inhibit microbial growth. The efficacy of wetted oxidized copper layers and pure copper surfaces as antimicrobial agents was tested by applying cultures of Escherichia coli and Staphylococcus cohnii to these metallic surfaces. Stainless steel surfaces were used as non-inhibitory control surfaces. The production of reactive oxygen species and membrane damage increased rapidly within 1 h of exposure on pure copper surfaces, but the effect on cell survival was negligible even after 2 h of exposure. However, longer exposure times of up to 4 h led to a rapid decrease in cell survival, whereby the survival of cells was additionally dependent on the exposed cell density. Finally, the release of metal ions was determined to identify a possible correlation between copper ions in suspension and cell survival. These measurements indicated a steady increase of free copper ions, which were released indirectly by cells presumably through excreted complexing agents. These data indicate that the application of antimicrobial surfaces in spaceflight facilities could improve crew health and mitigate material damage caused by microbial contamination and biofilm formation. Furthermore, the results of this study indicate that cuprous oxide layers were superior to pure copper surfaces related to the antimicrobial effect and that cell density is a significant factor that influences the time dependence of antimicrobial activity. Key Words: Contact killing-E. coli-S. cohnii-Antimicrobial copper surfaces-Copper oxide layers-Human health-Planetary protection. Astrobiology 17, 1183-1191.

To study the effects of heat shock on Deinococcus radiodurans and the role of DNA repair in high temperature resistance, different strains of D. radiodurans (wild type, recA, irrE, and pprA) were treated with temperatures ranging from 40 to 100 °C under wet and dry conditions. The mutant strains were more sensitive to wet heat of ≥60 °C and dry heat of ≥80 °C than the wild type. Both wild-type and DNA repair-deficient strains were much more resistant to high temperatures when exposed in the dried state as opposed to cells in suspension. Molecular staining techniques with the wild-type strain revealed that cells in the dried state were able to retain membrane integrity after drying and subsequent heat exposure, while heat-exposed cells in suspension showed significant loss of membrane integrity and respiration activity. The results suggest that the repair of DNA damage (e.g., DNA double-strand breaks by RecA and PprA) is essential after treatment with wet heat at temperatures >60 °C and dry heat >80 °C, and the ability of D. radiodurans to stabilize its plasma membrane during dehydration might represent one aspect in the protection of dried cells from heat-induced membrane damage.