The Structure of Resting Bacterial Populations in Soil and Subsoil Permafrost

Abstract

The structure of individual cells in microbial populations in situ of the Arctic and Antarctic permafrost was studied by scanning and transmission electron microscopy methods and compared with that of cyst-like resting forms generated under special conditions by the non-spore-forming bacteria Arthrobacter and Micrococcus isolated from the permafrost. Electron microscopy examination of microorganisms in situ revealed several types of bacterial cells having no signs of damage, including "dwarf" curved forms similar to nanoforms. Intact bacterial cells in situ and frozen cultures of the permafrost isolates differed from vegetative cells by thickened cell walls, the altered structure of cytoplasm, and the compact nucleoid, and were similar in these features to cyst-like resting forms of non-spore-forming "permafrost" bacterial strains of Arthrobacter and Micrococcus spp. Cyst-like cells, being resistant to adverse external factors, are regarded as being responsible for survival of the non-spore-formers under prolonged exposure to subzero temperatures and can be a target to search for living microorganisms in natural environments both on the Earth and on extraterrestrial bodies.

Brine Assemblages of Ultrasmall Microbial Cells within the Ice Cover of Lake Vida, Antarctica

“…None of the bacterial groups detected in the LVBrUMA have been reported as ultramicrobacteria (small cells that maintain their size and volume regardless of the growth condition). The morphology observed in the brine ultrasmall microbial cells is comparable to that of cells with pleomorphic life cycles (emerging to ultrasmall cells in late life cycle stage), cyst-like resting cells, and cells exposed to stressful osmotic conditions (66,67). Morphological transition is a genetically controlled phenomenon prevalent in bacterial life cycles and correlated to aging (68)(69)(70).…”

“…Morphological transition is a genetically controlled phenomenon prevalent in bacterial life cycles and correlated to aging (68)(69)(70). For example, Actinobacteria, including Arthrobacter (66,71) and Microbacterium (72), can be pleomorphic, meaning they can shift to ultrasmall cells during their life cycle. Likewise, unfavorable environmental conditions have been attributed to small cell size in Pseudomonas, Micrococcus, and Arthrobacter, which have been described with reduced cellular activity and size and a thick cellular envelope (73,74).…”

“…Likewise, unfavorable environmental conditions have been attributed to small cell size in Pseudomonas, Micrococcus, and Arthrobacter, which have been described with reduced cellular activity and size and a thick cellular envelope (73,74). Cyst-like resting cells from Arthrobacter globiformis isolated from Siberian permafrost were characterized as dwarf forms of 0.2 m in diameter, exhibiting a thick cell wall with an external capsular layer and low-electron-dense cytoplasm (66), similar to what we observed in this study with the Lake Vida ultrasmall microbial cells. Further, hyperosmotic stress can result in cell shrinkage as a consequence of water loss (Fig.…”

Super-long anabiosis of ancient microorganisms in ice and terrestrial models for development of methods to search for life on Mars, Europa and other planetary bodies

“…2). The examinations of native bacterial populations in permahost samples of different genesis and age showed the presence of both Gram-negative and Gram-positive bacteria after long-term exposure (7 thousands to 2 million years) to subzero temperatures (Soina et al, 2004). According to observations using the transmission electron microscope most of bacterial cells preserved the integrity.…”

Biofilm Formation by Psychrobacter arcticus and the Role of a Large Adhesin in Attachment to Surfaces

“…Biofilm formation may facilitate hydration in P. arcticus's natural environment, the Siberian permafrost, where the only unfrozen water is found as thin films surrounding soil, organic, and mineral particles (13)(14)(15). Scanning microscopy of Siberian permafrost soils has revealed tight associations between bacteria and soil particles (16,17). Based on these observations, we hypothesize that P. arcticus is able to fasten to surfaces near unfrozen water in the permafrost and that this attachment will provide the bacterium with access to unfrozen water, ultimately increasing survivability in the permafrost environment.…”