Earth scientists have searched for signs of microscopic lifein ancient samples of permafrost, ice, deep-see sediments,amber, salt and chert. Until now cyanobacteria were notreported in any studies of ancient DNA. We investigatemorphologically, biochemically and genetically the depositionof in situ, primary evaporites deposited during thelate Miocene (Messinian) Salinity Crisis from the northeasternApennines of Italy. The evaporites contain fossilizedcharacteristic filamentous structures that remainintact as long as the sulphate deposits are not altered andclearly evident within preserved crystals having identicalmorphological forms as modern biota from hypersalinesettings (bacteria, cyanobacteria and algae). Althoughstudies of ancient DNA are complicated by the extremesensitivity of analytical techniques to DNA contamination,requiring adequate test procedures for both experimentaland authentication methodology, we successfully extractedand amplified genetic material belonging to ancientcyanobacteria from gypsum crystals dating back to 5.910-5.816 million years ago, when the Mediterranean becamea giant hypersaline brine pool. These cyanobacterial rRNAsequences represent the oldest known cyanobacterial DNAever isolated. The age of this DNAis inferred from the primarynature of the host crystals, and the lack of contaminationin any of the sampled crystals.Our clone library andits phylogenetic comparison with present cyanobacterialpopulations point to a marine origin for the depositionalbasin. We also demonstrate here that genetic signals ofcyanobacterial 16S rDNA and bacterial 16S rDNA can bepreserved in gypsum deposits. This means that the primaryselenite may act as effective seal for materials trapped duringtheir growth. Several previous studies isolated sporeformingmicrobes that could be thought to survive suchlong-term suspension as cryptobiotic spores using bothancient halite and amber, but no previous studies havebeen done using gypsum crystals. Our investigation opensthe possibility of including cyanobacteria and their DNAinto paleo-reconstruction of various environments. Theseserve as biosignatures providing important clues aboutancient life and begin new discussion concerning the possibilityto use terrestrial evaporite settings as analogues ofhydrated sulfate deposits documented on the surface ofMars.
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|Data di pubblicazione:||2009|
|Autori:||PANIERI G. ; PALINSKA K.A.; LUGLI S.; MANZI V.;ROVERI M.; SCHREIBER B. C.|
|Titolo:||THE OLDEST RIBOSOMAL RNA GENE FRAGMENTS OF CYANOBACTERIA IDENTIFIED IN PRIMARY GYPSUM FROM THE LATE MIOCENE, ITALY|
|Appare nelle tipologie:||Abstract in Atti di Convegno|
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