Changes in the cell ultrastructure of the haloalkaliphilic endoevaporite cyanobacterium <Emphasis Type="Italic">‘Euhalothece natronophila’</Emphasis> during fossilization |
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Authors: | O I Baulina O S Samylina L M Gerasimenko |
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Institution: | 1.Faculty of Biology,Moscow State University,Moscow,Russia;2.Winogradsky Institute of Microbiology,Russian Academy of Sciences,Moscow,Russia |
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Abstract: | The ultrastructure of the haloalkaliphilic endoevaporite cyanobacterium ‘Euhalothece natronophila’ Z-M001 from the soda Lake Magadi was investigated during the initial stages of fossilization in a model experimental system.
The cyanobacterium was cultivated in concentrated carbonate solution supplemented with calcium chloride. It was revealed that
the amorphous CaCO3 formed under these conditions could interact with the cell wall during the first stages of ‘E. natronophila’ calcification. Evidence is presented that the surface layer of the ‘E. natronophila’ envelope, presumably containing polysaccharide and/or (glyco)protein components, can be involved in the adsorption and subsequent
crystallization of CaCO3 with the formation of a massive “shell” embedding the morphologically intact cells. It was established that the ultrastructure
of the cell wall and the intrathylakoid space changed during CaCO3 mineralization. During the later fossilization stages, cells covered by the calcium-containing “shell” were apparently mummified,
and mostly retained their original shape. The encapsulation of cyanobacteria in the trona globule was characterized by a different
pattern. It probably involved tight binding of the growing crystal to the glycocalyx components that are anchored in the outer
membrane. This may result in its detachment from the underlying peptidoglycan layer. The peptidoglycan was retained, and the
protoplasts were ultrastructurally similar to the intact ones. Cyanobacteria incorporated in large trona crystals underwent
degradation, deformation, and destruction. This accounts for the fact that massive trona deposits of Lake Magadi lack cyanobacterial
fossils that are abundant in calcium-containing strata. |
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