Phytoplankton RNA/DNA and 18S rRNA/rDNA ratios in a coastal marine ecosystem

Abstract

The RNA/DNA ratio is used as indicator of growth in various marine organisms and to assess physiological status at species or community level. To evaluate the utility of the RNA/DNA ratio as a proxy of phytoplankton primary production, the relationships between phytoplankton RNA/DNA, taxon-specific diatom and dinoflagellate 18S rRNA/rDNA ratios and autotrophic phytoplankton biomass were investigated as a first step. Significant correlations between all phytoplankton ratios and total phytoplankton, diatom and dinoflagellate biomass as chlorophyll a (chl a) and carbon content were found. Diatoms showed higher correlation than dinoflagellates (18S rRNA/rDNA vs. chl a, rs = 0.74 and 0.64, P < 0.001; 18S rRNA/rDNA vs. carbon, rs = 0.66 and 0.53, P < 0.001, respectively), because they represented the most abundant and frequent group within sampled assemblages. Further, phytoplankton biomass production is known to be linked to protein biosynthesis and significant relationships between RNA/DNA ratios and protein content of phytoplankton assemblage were found (rs = 0.62 and 0.52, P < 0.001 for diatom and dinoflagellates, respectively). As taxon-specific RNA/DNA ratios were correlated with biomass and protein content, our results can be regarded as the first step toward further studies on the applicability of RNA/DNA ratios as indicators of growth rate and primary production in phytoplankton assemblages.

RNA/DNA ratios as estimate of metabolic and functional traits in diatom species from the northwestern Adriatic Sea

“…Total genomic DNA, RNA and proteins from individual and co-cultured cultured samples of C. socialis CBA22 and S. marinoi CBA4 were extracted using the RNA/DNA/Protein Purification Plus Kit (Norgen Biotek Corp., Thorold, Canada) according to the manufacturer's instructions. The nucleic acids and proteins quantification and the cDNA preparation protocols were reported in Casabianca et al (2021). The diatoms 18S rRNA/rDNA ratio was calculated using class-specific primers targeting diatoms taxa (Casabianca et al 2021), while Chaetoceros spp.…”

“…The nucleic acids and proteins quantification and the cDNA preparation protocols were reported in Casabianca et al (2021). The diatoms 18S rRNA/rDNA ratio was calculated using class-specific primers targeting diatoms taxa (Casabianca et al 2021), while Chaetoceros spp. and Skeletonema spp.…”

“…(Nejstgaard et al, 2003;Berdalet et al, 2005;Ikeda et al, 2007;Finkel et al, 2016). It has previously been shown that the diatom and dinoflagellate 18S rRNA/rDNA ratios measured within phytoplankton assemblages were significantly correlated to biomass, and because this molecular parameter is linked to cellular RNA variability, it has the potential to express the growth rate and metabolic dynamics of phytoplankton assemblages (Dortch et al, 1983;Nicklisch and Steinberg, 2009;Casabianca et al, 2021).…”

“…Seasonal diatom blooms, which are frequently monospecific or mixed by co-occurring dominating diatom taxa, such as Chaetoceros spp. and Skeletonema marinoi, are of importance in this Adriatic region (Cabrini et al, 2012;Totti et al, 2019;Casabianca et al, 2021;Casabianca et al, 2022;Neri et al, 2023). The high-density blooms are sustained by nutrient availability from turbulent waters and riverine inputs from both Po and minor river discharges (Bernardi Aubry et al, 2004;Penna et al, 2004;Mangoni et al, 2008;Socal et al, 2008;Mangoni et al, 2013;Penna et al, 2013;Ricci et al, 2022), as well as diatom high nutrient uptake rates (Litchman et al, 2007).…”

Ecological implications beyond the ecotoxicity of plastic debris on marine phytoplankton assemblage structure and functioning

“…Further studies considering natural plankton assemblages and/or large mesocosm experiments should be performed with the aim of evaluating the ecological relevance of both MPs and nanoplastics/phytoplankton assemblage interaction. Similar approaches, near to real marine environmental conditions, should be applied also to phytoplankton assemblages in order to study global MPs and nanoplastics effects by evaluating indirect indicators of productivity, as growth rate, abundance, species composition, carbon content, buoyancy, macromolecules composition (DNA, RNA, proteins, carbohydrates, lipids) and their ratios, photosynthetic efficiency and, therefore, ecological implications on the functioning of the phytoplankton communities in the food web (Casabianca et al, 2021).…”