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Applied and Environmental Microbiology, September 2004, p. 5459-5468, Vol. 70, No. 9
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.9.5459-5468.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Geochemical Rate-RNA Integration Study: Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Gene Transcription and Photosynthetic Capacity of Planktonic Photoautotrophs

Department of Marine Sciences, University of Puerto Rico, Lajas, Puerto Rico,¹ College of Marine Science, University of South Florida, St. Petersburg, Florida,² Institute of Marine and Coastal Sciences, Rutgers University, New Brunswick, New Jersey³

Received 15 October 2003/ Accepted 5 May 2004

A pilot field experiment to assess the relationship between traditional biogeochemical rate measurements and transcriptional activity of microbial populations was carried out at the LEO 15 site off Tuckerton, N.J. Here, we report the relationship between photosynthetic capacity of autotrophic plankton and transcriptional activity of the large subunit gene (rbcL) for ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO), the enzyme responsible for primary carbon fixation during photosynthesis. Similar diel patterns of carbon fixation and rbcL gene expression were observed in three of four time series, with maxima for photosynthetic capacity (P_max) and rbcL mRNA occurring between 10 a.m. and 1 p.m.. The lowest P_max and rbcL levels were detected between 6 p.m. and 10:30 p.m.. A significant correlation was found between P_max and form ID rbcL mRNA (R² = 0.56) and forms IA and IB (R² = 0.41 and 0.47, respectively). The correlation between the abundance of "diatom" rbcL and P_max mRNA was modest (R² = 0.49; n = 12) but improved dramatically (R² = 0.97; n = 10) upon removal of two outliers which represented afternoon samples with high P_max but lower mRNA levels. Clone libraries from reverse transcription-PCR-amplified rbcL mRNA indicated the presence of several chromophytic algae (diatoms, prymnesiophytes, and chrysophytes) and some eukaryotic green flagellates. Analogous results were obtained from amplified small rRNA sequences and secondary pigment analysis. These results suggest that diatoms were a major contributor to carbon fixation at LEO 15 at the time of sampling and that photosynthetic carbon fixation was partially controlled by transcriptional regulation of the RubisCO gene.