Metal-macrofauna interactions determine microbial community structure and function in copper contaminated sediments

Peer reviewedPublisher PD

The TATA-binding protein regulates maternal mRNA degradation and differential zygotic transcription in zebrafish

Early steps of embryo development are directed by maternal gene products and trace levels of zygotic gene activity in vertebrates. A major activation of zygotic transcription occurs together with degradation of maternal mRNAs during the midblastula transition in several vertebrate systems. How these processes are regulated in preparation for the onset of differentiation in the vertebrate embryo is mostly unknown. Here, we studied the function of TATA-binding protein (TBP) by knock down and DNA microarray analysis of gene expression in early embryo development. We show that a subset of polymerase II-transcribed genes with ontogenic stage-dependent regulation requires TBP for their zygotic activation. TBP is also required for limiting the activation of genes during development. We reveal that TBP plays an important role in the degradation of a specific subset of maternal mRNAs during late blastulation/early gastrulation, which involves targets of the miR-430 pathway. Hence, TBP acts as a specific regulator of the key processes underlying the transition from maternal to zygotic regulation of embryogenesis. These results implicate core promoter recognition as an additional level of differential gene regulation during development

Seasonal variations in pore water and sediment geochemistry of littoral lake sediments (Asylum Lake, MI, USA)

BACKGROUND: Seasonal changes in pore water and sediment redox geochemistry have been observed in many near-surface sediments. Such changes have the potential to strongly influence trace metal distribution and thus create seasonal fluctuations in metal mobility and bioavailability. RESULTS: Seasonal trends in pore water and sediment geochemistry are assessed in the upper 50 cm of littoral kettle lake sediments. Pore waters are always redox stratified, with the least compressed redox stratification observed during fall and the most compressed redox stratification observed during summer. A 2-step sequential sediment extraction yields much more Fe in the first step, targeted at amorphous Fe(III) (hydr)oxides (AEF), then in the second step, which targets Fe(II) monosulfides. Fe extracted in the second step is relatively invariant with depth or season. In contrast, AEF decreases with sediment depth, and is seasonally variable, in agreement with changes in redox stratification inferred from pore water profiles. A 5-step Tessier extraction scheme was used to assess metal association with operationally-defined exchangeable, carbonate, iron and manganese oxide (FMO), organic/sulfide and microwave-digestible residual fractions in cores collected during winter and spring. Distribution of metals in these two seasons is similar. Co, As, Cd, and U concentrations approach detection limits. Fe, Cu and Pb are mostly associated with the organics/sulfides fraction. Cr and Zn are mostly associated with FMO. Mn is primarily associated with carbonates, and Co is nearly equally distributed between the FMO and organics/sulfide fractions. CONCLUSION: This study clearly demonstrates that near-surface lake sediment pore water redox stratification and associated solid phase geochemistry vary significantly with season. This has important ramifications for seasonal changes in the bioavailability and mobility of trace elements. Without rate measurements, it is not possible to quantify the contribution of various processes to natural organic matter degradation. However, the pore water and solid phase data suggest that iron reduction and sulfate reduction are the dominant pathways in the upper 50 cm of these sediments

Use of high temperature catalytic oxidation (HTCO) to measure carbon content of microorganisms

International audienceHigh temperature catalytic oxidation (HTCO) was used for the first time to determine carbon content of heterotrophic protists (the helioflagellate Pteridomonas danica, the dinoflagellate Oxyrrhis marina, and the scuticociliate Uronema sp.) and bacteria (Escherichia coli). This technique has the advantage, over the conventional CHN analysis of glass-fiber filters, of measuring total organic carbon in the liquid phase. Failing to retain small organisms on filters and cell rupture during filtration can thus be avoided. Cell volumes were measured on live (Coulter Counter) and Lugol's iodine- or formaldehyde-preserved cells and used to obtain a carbon:biovolume conversion factor for each species. Carbon:biovolume conversion factors ranged from 123 to 175 and from 121 to 864 fg C mu m(-3) for live and preserved cells, respectively. A linear regression of cell carbon content versus live biovolume gave a mean carbon:biovolume conversion factor of 125.3 +/- 7.6 (SE) fg C mu m(-3) for the 4 species studied with biovolumes ranging from 0.69 to 1590 mu m(3) The data obtained in this study is compared to live and preserved cells data obtained from the literature and the possibility of using a single carbon:biovolume conversion factor for bacteria and protozoa is discussed

Particulate and dissolved organic carbon production by the heterotrophic nanoflagellate Pteridomonas danica Patterson and Fenchel

We established a budget of organic carbon utilization of a starved heterotrophic nanoflagellate, Pteridomonas danica, incubated in batch cultures with Escherichia coli as model prey. The cultures were sampled periodically for biomass determinations and total organic carbon dynamics: total organic carbon, total organic carbon <1 mu m, and dissolved organic carbon (DOC, <0.2 mu m). During the 22 h incubation period, P. danica underwent biovolume variations of 3.2-fold. Gross growth efficiency was 22% and net growth efficiency 40%. P. danica respired 33% and egested 44% of the ingested E. coli carbon during lag and exponential growth phases. The form of the organic carbon egested varied. Of the total ingested carbon, 9% was egested in the form of DOC and occurred mainly during the exponential growth phase; 35% was egested in the form of particulate organic carbon (POC), ranging in size from 0.2 to 1 mu m, and took place during the lag phase. P, danica could have reingested as much of 58% of this previously produced POC during the exponential growth phase as food scarcity increased. We concluded that POC egestion by flagellates could represent a significant source of submicrometric particles and colloidal organic matter. In addition, flagellate reingestion of egested POC could play a nonnegligible role in the microbial Food web. Finally, the methodology reported in this study has proved to be a useful tool in the study of carbon metabolism in aquatic microorganisms