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Applied and Environmental Microbiology, September 1998, p. 3238-3245, Vol. 64, No. 9
Faculty of Science,
Received 10 November 1997/Accepted 4 April 1998
In this study, we compared three methods for extraction and
quantification of RNA and DNA from marine sediments: (i) a
spectrophotometric method using the diphenylamine assay; (ii) a
fluorometric method utilizing selective fluorochromes (thiazole orange
for total nucleic acids and Hoechst 33258 for DNA); and (iii) a
high-pressure liquid chromatography (HPLC) method which uses a specific
column to separate RNA and DNA and UV absorption of the nucleic acids
for quantification. Sediment samples were collected in the oligotrophic
Cretan Sea (eastern Mediterranean, from 40 to 1,540 m in depth) and
compared to the distribution and composition of the benthic microbial
assemblages (i.e., bacteria and microprotozoa). DNA concentrations
measured spectrophotometrically and by HPLC were not significantly
different, while fluorometric yields were significantly lower. Such
differences appear mainly due to fact that the stain-DNA complex is
strongly dependent on the DNA composition and structure. RNA
concentrations determined by the three methods displayed some
differences; fluorometric and spectrophotometric methods obtain RNA
concentration by difference and therefore may be biased by DNA
estimates. By contrast, the HPLC method provides independent
assessments of RNA and DNA concentrations. We tentatively estimated the
contribution of the detrital DNA to the total DNA pools in two ways.
The two calculations provided quite similar results indicating that the
majority of the DNA pool in the deep-sea sediments was detrital.
Microbial RNA generally accounted for almost the entire sedimentary RNA
pools below 100-m depth. RNA concentrations were found to decrease
along the Cretan shelf and slope. The RNA/DNA ratio calculated by using
fluorometric DNA concentrations was significantly correlated with
values of sediment community oxygen consumption only below 100-m depth
(dominated by the microbial biomass). These data suggest that the
RNA/DNA ratio, based on fluorometric estimates of DNA, can be used as an indicator of benthic metabolic activity, but only when metazoan contribution to the microbial DNA is negligible.
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Nucleic Acid (DNA, RNA) Quantification and RNA/DNA Ratio
Determination in Marine Sediments: Comparison of Spectrophotometric,
Fluorometric, and HighPerformance Liquid Chromatography
Methods and Estimation of Detrital DNA
*
Corresponding author. Mailing address: Marine Science,
Facoltà di Scienze, Università di Ancona, Via Brecce
Bianche, 60131 Ancona, Italy. Phone: 39 71 2204652. Fax: 39 71 2204513. E-mail: danovaro{at}popcsi.unian.it.
Applied and Environmental Microbiology, September 1998, p. 3238-3245, Vol. 64, No. 9
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
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