Influence of various redox conditions on the degradation of microalgal triacylglycerols and fatty acids in marine sediments

Sediment cakes, supplemented with microalgal cells (Nannochloropsis salina), were incubated for 35 days under permanently oxic, oscillating (5d:5d changeover oxic/anoxic) and strictly anoxic conditions of oxygenation in diffusively ‘‘open’’ sedimentary systems. Total lipids (TLip) and triacylglycerols (TG) concentrations were monitored by thin layer chromatography-flame ionisation detection, whereas the concentrations of the main extractable (free+ester-bound) individual fatty acids (C16:0, C16:1, C18:1) were followed using gas chromatography-mass spectrometry. Under the three conditions of oxygenation, TOC, TLip and TG showed a sharp decrease in concentration during the early days of incubation and seemed to stabilise thereafter, defining an apparent non degradable fraction (GNR). The GNR content was systematically higher in the anoxic incubation than under the oxic and oscillating conditions. The ratio of the main hydrolysis products of TG versus TG [(Free fatty acids+Monoacylglycerols+1,2-Diacylglycerols)/TG], used as an indicator of the hydrolysis of TG, showed that the presence of oxygen in the sediments (oxic and oscillating conditions) stimulates the hydrolysis of TG and the subsequent degradation of their metabolites. Unlike TOC, TLip and TG, individual fatty acids (FA) showed a continuous concentration decrease until the end of the experiment, which was fitted with a simple first order model [G(t)=G0e_kt] to yield apparent degradation rate constants. The values observed under oscillating conditions (kFA=0.019 +/- 0.001 d_1) were intermediate to those observed during oxic (kFA=0.029 +/- 0.003 d_1) and anoxic (kFA=0.011 +/- 0.001 d_1) incubations, and no significant difference between individual FA could be observed. The production of saturated and monounsaturated C16 (and to a lesser extent C18) alkanols under oscillating and anoxic redox conditions suggested that (a part of) the dominant FA were reduced to the corresponding alcohols under anoxic conditions, following their release from acylglycerols

Burial and reactivity of sedimentary microalgal lipids in bioturbated Mediterranean coastal sediments

International audienceThe fate of microalgal lipid biomarkers in marine coastal sediments when acted on by natural bioturbation processes (Carteau Bay, Gulf of Fos, Mediterranean Sea) was studied under laboratory conditions. Both dead phytoplanktonic cells (Nannochloropsis salina) and luminophores (inert fluorescent particulate tracers) were deposited at the surface of intact sediment cores which were then incubated for 22, 44 and 63 days. Sediment reworking and concentration profiles of specific lipid components of N. salina (n-alkenes, alkyl diols, sterols and fatty acids) were determined as a function of time and depth. The results show that, in the sediment investigated, bioturbation occurs essentially as a biodiffusive process and that it has a rapid and significant impact on the qualitative and quantitative record of sedimentary lipids. Whereas most of the biomarkers were detected in the entire reworked layer (0â6 cm) after 22 days, n-alkenes were never detected below 3 cm due to their low concentration and their high reactivity. For each individual lipid, the comparison of the amounts obtained from the inventories of biomarkers in the reworked zone, with the amount deposited initially at the sediment surface, allowed the determination of its extent and rate of degradation. These ranged from 72% to 99% and from 0.010 to 0.047 day-1, respectively, depending on the biomarker considered, with polyunsaturated fatty acids (PUFAs) and alkenes being degraded faster than the other components. Comparison with previous work suggests that, in biologically reworked sediments, the apparent reactivity of lipids is: (i) positively correlated with the biological mixing coefficient (Db) and, (ii) generally much higher than in non-bioturbated (anoxic) sediments. Our results also support the idea that degradation of lipids in reworked sediments involves the combined effects of aerobic and anaerobic degradation processes, but that biological mixing results in diagenetic properties more characteristic of completely oxidized conditions

Macrofaunal reworking activities and hydrocarbon redistribution in an experimental sediment system

The influence of macrofaunal reworking activities on the redistribution of particle associated hydrocarbon compounds (HC)was experimentally investigated. Two distinct hydrocarbon mixtures adsorbed on montmorillonite particles ( < 4 Am diameter)were added to the surface and deeper (2.5 cm) sediment layers. For comparison, luminophores (100–160 Amdiameter) were added in the two deposit layers. At the start of the experiment, four macrobenthic species (the bivalve Abra nitida, the polychaete Scalibregma inflatum, and the echinoderms Amphiura filiformis and Echinocardium cordatum) were added to the sediment surface. The macrofauna added rapidly transferred HC from the surface sediment down to f5 cm depth by both continuous (biodiffusion) and non-continuous (biotransport) transport. Hydrocarbon compounds initially added to the deeper sediment layer were only subject to biodiffusion-like transport. Apparent biodiffusion coefficients (Db) quantified by using a 1-D model were between 0.5 and 8.4×10−3 cm 2 d−1, and biotransport coefficients (r) ranged from 2.0 to 27.6×10−3 d−1. Thus, the four species studied did not have the same effect on particle redistribution and, consequently, on HC repartition in the sediments. E. cordatum was the most efficient reworker. The present study demonstrated the importance of particle size selectivity by benthic fauna, and verified that macrofaunal reworking activities may redeposit sediment from deeper sediment layers on the sediment surface. Both processes have obvious implications for rates and pathways during organic matter mineralisation in marine sediments

Treatment of heavy petroleum hydrocarbons polluted soil leachates by ultrafiltration and oxidation for surfactant recovery

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Compatibility of surfactants with activated-persulfate for the selective oxidation of PAH in groundwater remediation

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Therapy-induced developmental reprogramming of prostate cancer cells and acquired therapy resistance

Treatment-induced neuroendocrine transdifferentiation (NEtD) complicates therapies for metastatic prostate cancer (PCa). Based on evidence that PCa cells can transdifferentiate to other neuroectodermally-derived cell lineages in vitro, we proposed that NEtD requires first an intermediary reprogramming to metastable cancer stem-like cells (CSCs) of a neural class and we demonstrate that several different AR+/PSA+ PCa cell lines were efficiently reprogrammed to, maintained and propagated as CSCs by growth in androgen-free neural/neural crest (N/NC) stem medium. Such reprogrammed cells lost features of prostate differentiation; gained features of N/NC stem cells and tumor-initiating potential; were resistant to androgen signaling inhibition; and acquired an invasive phenotype in vitro and in vivo. When placed back into serum-containing mediums, reprogrammed cells could be re-differentiated to N-/NC-derived cell lineages or return back to an AR+ prostate-like state. Once returned, the AR+ cells were resistant to androgen signaling inhibition. Acute androgen deprivation or anti-androgen treatment in serum-containing medium led to the transient appearance of a sub-population of cells with similar characteristics. Finally, a 132 gene signature derived from reprogrammed PCa cell lines distinguished tumors from PCa patients with adverse outcomes. This model may explain neural manifestations of PCa associated with lethal disease. The metastable nature of the reprogrammed stem-like PCa cells suggests that cycles of PCa cell reprogramming followed by re-differentiation may support disease progression and therapeutic resistance. The ability of a gene signature from reprogrammed PCa cells to identify tumors from patients with metastasis or PCa-specific mortality implies that developmental reprogramming is linked to aggressive tumor behaviors