Publications (3)11.2 Total impact
Article: Phytoplankton carbon fixation gene (RuBisCO) transcripts and air-sea CO(2) flux in the Mississippi River plume.[show abstract] [hide abstract]
ABSTRACT: River plumes deliver large quantities of nutrients to oligotrophic oceans, often resulting in significant CO(2) drawdown. To determine the relationship between expression of the major gene in carbon fixation (large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase, RuBisCO) and CO(2) dynamics, we evaluated rbcL mRNA abundance using novel quantitative PCR assays, phytoplankton cell analyses, photophysiological parameters, and pCO(2) in and around the Mississippi River plume (MRP) in the Gulf of Mexico. Lower salinity (30-32) stations were dominated by rbcL mRNA concentrations from heterokonts, such as diatoms and pelagophytes, which were at least an order of magnitude greater than haptophytes, alpha-Synechococcus or high-light Prochlorococcus. However, rbcL transcript abundances were similar among these groups at oligotrophic stations (salinity 34-36). Diatom cell counts and heterokont rbcL RNA showed a strong negative correlation to seawater pCO(2). While Prochlorococcus cells did not exhibit a large difference between low and high pCO(2) water, Prochlorococcus rbcL RNA concentrations had a strong positive correlation to pCO(2), suggesting a very low level of RuBisCO RNA transcription among Prochlorococcus in the plume waters, possibly due to their relatively poor carbon concentrating mechanisms (CCMs). These results provide molecular evidence that diatom/pelagophyte productivity is largely responsible for the large CO(2) drawdown occurring in the MRP, based on the co-occurrence of elevated RuBisCO gene transcript concentrations from this group and reduced seawater pCO(2) levels. This may partly be due to efficient CCMs that enable heterokont eukaryotes such as diatoms to continue fixing CO(2) in the face of strong CO(2) drawdown. Our work represents the first attempt to relate in situ microbial gene expression to contemporaneous CO(2) flux measurements in the ocean.The ISME Journal 11/2007; 1(6):517-31. · 7.38 Impact Factor
Article: Geochemical rate-RNA integration study: ribulose-1,5-bisphosphate carboxylase/oxygenase gene transcription and photosynthetic capacity of planktonic photoautotrophs.[show abstract] [hide abstract]
ABSTRACT: 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 (R(2) = 0.56) and forms IA and IB (R(2) = 0.41 and 0.47, respectively). The correlation between the abundance of "diatom" rbcL and P(max) mRNA was modest (R(2) = 0.49; n = 12) but improved dramatically (R(2) = 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.Applied and Environmental Microbiology 10/2004; 70(9):5459-68. · 3.83 Impact Factor
Article: Analysis of the optical properties of the Orinoco River plume by absorption and fluorescence spectroscopy[show abstract] [hide abstract]
ABSTRACT: The discharge of the Orinoco River significantly affects the optical properties of the water in the Caribbean Sea by increasing primary productivity and introducing large amounts of colored dissolved organic matter (CDOM) to the region. The optical characteristics of the CDOM in the Orinoco River plume were investigated during two cruises to the eastern Caribbean using absorption and fluorescence spectroscopy. We found that high concentrations of dissolved organic carbon (DOC) and abundance of CDOM in the eastern Caribbean were related to the Orinoco River plume. We did not observe changes in optical properties of CDOM in waters with salinities lower than 30. Self-shading from sunlight and the preponderance of riverine material at these low salinities can explain the observed behavior. Changes in the optical properties of the CDOM were observed in stations with salinities higher than 30 and were related to mixing between riverine and marine end-members, and to photodegradation. Light penetration and, consequently, the position of the chlorophyll maxima in areas close to the Gulf of Paria were controlled by the concentration of CDOM. Of the two main fluorophores found in this study, only the humic fluorophore appeared to be related to the absorption of light by CDOM in the visible spectrum. A secondary fluorophore, with excitation and emission in the UV, appeared to be resistant to photodegradation and did not show any relationship with absorbance in the visible range.Marine Chemistry.