Cultivation-indipendent assessment of the batthypelagic archaeal diversity of Tyrrhenian Sea:comparative study of rDNA-derived libraries and influence of samples decompression

Two samples of the same bathypelagic bacterioplankton community (Tyrrhenian Sea at the depth of 3000 m) were collected during single cast by both traditional sampling with Niskin bottle and using a high pressure-maintaining HPSS sampler. Total RNA was isolated, reverse transcribed, amplified with Archaea-specific primers and cloned. Riboclones were sequenced, 117 riboclones from decompressed library and 104 rRNA-based riboclones retrieved from HPSS sampler. Both RNA libraries were additionally compared with 115 riboclones based on DNA obtained from the decompressed sample (16S rRNA genes). In terms of repetitive riboclones, obtained in all three libraries, the bathypelagic community was dominated by Crenarchaeota Marine Group I (52-64%). The combined analysis led to a characterization of sampling-specific phylotypes otherwise uncharacterized if only one type of library had been analyzed alone. Of the DNA riboclones, 22% were found only in this library and no close relatives of Euryarchaeota Marine Group II were detected in both RNA-based libraries, suggesting the dormant state of these organisms in deep-sea environment. For clones from the RNA libraries, one Crenarchaeota MG I phylotype did not indicate close relatives in the DNA library. In general, among 10 archaeal phylotypes recovered in total, 8, 7 and 6 of them were faced in DNA, RNA_HPSS and RNA decompressed libraries, respectively. Based on comparisons between all three libraries, our data indicate that (i) the short-term decompression of seawater samples during cast recovery and following treatments caused only slight changes in the total rRNA diversity and (ii) rRNA-based analysis is likely affected the characterization of phylotypes, present in deep-sea environment as the dormant cells, detected only on the DNA level.