Microbial Response of a Freshwater Benthic Community to a Simulated Diatom Sedimentation Event: Interactive Effects of Benthic Fauna

Abstract The response of a sediment microbial assemblage to a pulse of diatoms was studied over 36 days by measuring bacterial activity and biomass, ATP concentration, and overall community respiration in laboratory microcosms. Also, the contribution of macrofaunal chironomids to the decomposition of settling diatoms in benthic communities, and the relative importance of benthic meiofauna in community metabolism, were determined. The addition of diatoms resulted in an immediate response by sediment bacteria, with higher bacterial production recorded after only 2 h, and a more than tenfold increase within one day. The rapid response by sediment bacteria was accompanied by relatively high initial concentrations of dissolved organic carbon. In treatments receiving diatoms, higher bacterial production was sustained throughout the experiment. Surprisingly, neither these elevated production estimates, nor the starvation of controls affected bacterial abundance. Mean bacterial cell volume, however, was markedly affected by the addition of diatoms. Combining community respiration measurements and bacterial production estimates showed that growth efficiencies for sediment bacteria ranged from 14.6 to 34.5%. The contribution of ambient meiozoobenthos to carbon metabolism was less than 1%. Carbon budgets showed that 1.3 mg C was cooxidized along with 4.3 mg added diatom C. Sediment reworking by Chironomus larvae initially enhanced bacterial production, but the presence of Chironomus resulted in lower bacterial production estimates after 16 and 36 days. This was interpreted as a result of faster decomposition of diatoms in treatments with chironomids, which was validated by a faster decline of ATP and chlorophyll a in the sediment. Our results indicate that Chironomus larvae compete with sediment bacteria for available organic substrates. Received: 11 June 1996; Accepted: 13 August 1996     

7 Alpha-hydroxylation of cholesterol by reconstituted systems from rat liver microsomes

A reconstituted system from rat liver microsomes, consisting of partially purified fractions of cytochrome P-450 and NADPH-cytochrome P-450 reductase was shown to catalyze 7α-hydroxylation of cholesterol in the presence of NADPH and a synthetic phosphatidylcholine. The rate of 7α-hydroxylation of added [4-¹⁴C] cholesterol was linear with the concentration of cytochrome P-450 and increased with the concentration of NADPH-cytochrome P-450 reductase up to a certain level and then remained constant. Omission of phosphatidylcholine resulted only in a 20% decrease in cholesterol 7α-hydroxylase activity of the system. The rate of 7α-hydroxylation was 2–3 times higher in reconstituted systems with cytochrome P-450 from cholestyramine-treated rats than in those with cytochrome P-450 from untreated rats.     

12alpha-hydroxylation of 7alpha-hydroxy-4-cholesten-3-one by a reconstituted system from rat liver microsomes

A preparation of partially purified cytochrome P-450 from rat liver microsomes was found to catalyze 12α-hydroxylation of 7α-hydroxy-4-cholesten-3-one in the presence of NADPH and phosphatidyl choline. The reaction was stimulated two- to four-fold by addition of a preparation of cytochrome P-450 reductase. The reaction was inhibited by carbon monoxide to a considerably less extent than other hydroxylations catalyzed by the reconstituted system. In the presence of optimal concentrations of cytochrome P-450 reductase, cytochrome P-450 prepared from livers of starved rats catalyzed the 12α-hydroxylation more efficiently than cytochrome P-450 prepared from livers of normal rats or rats treated with phenobarbital.     

Time‐dependent climate impact and energy efficiency of combined heat and power production from short‐rotation coppice willow using pyrolysis or direct combustion

A life cycle assessment of a Swedish short‐rotation coppice willow bioenergy system generating electricity and heat was performed to investigate how the energy efficiency and time‐dependent climate impact were affected when the feedstock was converted into bio‐oil and char before generating electricity and heat, compared with being combusted directly. The study also investigated how the climate impact was affected when part of the char was applied to soil as biochar to act as a carbon sequestration agent and potential soil improver. The energy efficiencies were calculated separately for electricity and heat as the energy ratios between the amount of energy service delivered by the system compared to the amount of external energy inputs used in each scenario after having allocated the primary energy related to the inputs between the two energy services. The energy in the feedstock was not included in the external energy inputs. Direct combustion had the highest energy efficiency. It had energy ratios of 10 and 36 for electricity and heat, respectively. The least energy‐efficient scenario was the pyrolysis scenario where biochar was applied to soils. It had energy ratios of 4 and 12 for electricity and heat, respectively. The results showed that pyrolysis with carbon sequestration might be an option to counteract the current trend in global warming. The pyrolysis system with soil application of the biochar removed the largest amount of from the atmosphere. However, compared with the direct combustion scenario, the climate change mitigation potential depended on the energy system to which the bioenergy system delivered its energy services. A system expansion showed that direct combustion had the highest climate change mitigation potential when coal or natural gas were used as external energy sources to compensate for the lower energy efficiency of the pyrolysis scenario.     

FGF signals induce Caprin2 expression in the vertebrate lens

The lens of the eye is derived from the non-neural ectoderm situated next to the optic vesicle. Fibroblast growth factor (FGF) signals play a major role at various stages of vertebrate lens development ranging from induction and proliferation to differentiation. Less is however known about the identity of genes that are induced by FGF activity within the lens. We have isolated and characterized mouse cytoplasmic activation/proliferation-associated protein-2 (Caprin2), with domains belonging to both the Caprin family and the C1q and tumour necrosis factor (TNF) super-family. Here we show that Caprin2 is expressed in the developing vertebrate lens in mouse and chick, and that Caprin2 expression is up-regulated in primary lens fiber cells, after the induction of crystallins the earliest known markers for differentiated lens fiber cells. Caprin2 is subsequently down-regulated in the centre of the lens at the time and at the position of the first fiber cell denucleation and terminal differentiation. In vitro analyses of lens fiber cell differentiation provide evidence that FGF activity emanating from neighboring prospective retinal cells is required and that FGF8 activity is sufficient to induce Caprin2 in lens fiber cells. These results not only provide evidence that FGF signals induce the newly characterized protein Caprin2 in the lens, but also support the general idea that FGF signals are required for lens fiber cell differentiation.     

Oxysterols and neurodegenerative diseases

In contrast to their parent molecule cholesterol, two of its side-chain oxidized metabolites are able to cross the blood–brain barrier. There is a concentration-driven flux of 24S-hydroxycholesterol (24S-OHC) from the brain into the circulation, which is of major importance for elimination of excess cholesterol from the brain. The opposite flux of 27-hydroxycholesterol (27-OHC) from the circulation into the brain may regulate a number of key enzymes within the brain. In vitro experiments suggest that the balance between the levels of these two molecules may be of importance for the generation of β-amyloid peptides. In primary cultures of rat hippocampal cells 27-OHC is able to suppress expression of the activity regulated cytoskeleton-associated protein (Arc), a protein important in memory consolidation which is reduced in patients with Alzheimer’s disease (AD). In the present work we explore the possibility that the flux of 27-OHC from the circulation into the brain represents the missing link between AD and hypercholesterolemia, and discuss the possibility that modification of this flux may be a therapeutic strategy. Lastly, we discuss the use of oxysterols as diagnostic markers in neurodegenerative disease.