Responses of Haloarchaea to Simulated Microgravity

Abstract

Various effects of microgravity on prokaryotes have been recognized in recent years, with the focus on studies of pathogenic bacteria. No archaea have been investigated yet with respect to their responses to microgravity. For exposure experiments on spacecrafts or on the International Space Station, halophilic archaea (haloarchaea) are usually embedded in halite, where they accumulate in fluid inclusions. In a liquid environment, these cells will experience microgravity in space, which might influence their viability and survival. Two haloarchaeal strains, Haloferax mediterranei and Halococcus dombrowskii, were grown in simulated microgravity (SMG) with the rotary cell culture system (RCCS, Synthecon). Initially, salt precipitation and detachment of the porous aeration membranes in the RCCS were observed, but they were avoided in the remainder of the experiment by using disposable instead of reusable vessels. Several effects were detected, which were ascribed to growth in SMG: Hfx. mediterranei's resistance to the antibiotics bacitracin, erythromycin, and rifampicin increased markedly; differences in pigmentation and whole cell protein composition (proteome) of both strains were noted; cell aggregation of Hcc. dombrowskii was notably reduced. The results suggest profound effects of SMG on haloarchaeal physiology and cellular processes, some of which were easily observable and measurable. This is the first report of archaeal responses to SMG. The molecular mechanisms of the effects induced by SMG on prokaryotes are largely unknown; haloarchaea could be used as nonpathogenic model systems for their elucidation and in addition could provide information about survival during lithopanspermia (interplanetary transport of microbes inside meteorites).

Halophilic Archaea: Life with Desiccation, Radiation and Oligotrophy over Geological Times

“…From a fluid inclusion in a 97,000-year-old halite crystal from Death Valley, a strain of Halobacterium salinarum was isolated [ 9 ]. Cells within fluid inclusions can be visualized in laboratory-grown halite, as was demonstrated for the non-halophilic Pseudomonas aeruginosa [ 40 ] and several Haloarchaea [ 41 , 42 , 43 ]. Cells of a rod-shaped morphology, such as strains of Halobacterium salinarum , were converted to small roundish forms within the fluid inclusions, as shown in Figure 1 .…”

Evolutionary advantages of polyploidy in halophilic archaea

“…volcanii and Hcc. dombrowskii to simulated microgravity has also been analysed [22]. Most importantly, it was shown that a considerable fraction of Halococcus sp.…”

Efficient non-cytotoxic fluorescent staining of halophiles

“…immunostaining 36 , 37 , DAPI 38 , 39 , and FISH 38 , 40 ) or the use of DNA-targeted intercalating dyes (i.e. LIVE&DEAD kit 35 , 39 , 41 – 45 , Acridine Orange 43 , 46 , Hoechst 47 ). The latter approach is unsafe due to interference with the cellular DNA processing machinery, which can result in complete loss of cell viability (for review see 48 , 49 ).…”