Membrane lipid dynamics and enzymic activity in bovine adrenal cortex microsomes

The lipid dynamics of the adrenocortical microsomal membranes was studied by monitoring the fluorescence anisotropy and excited state lifetime of a set of anthroyloxy fatty acid probes (2-, 7-, 9- and 12-(9-anthroyloxy)-stearic acid (AP) and 16-(9-anthroyloxy)palmitic acid (AS). It was found that a decreasing polarity gradient from the aqueous membrane interface to the membrane interior, was present. This gradient was not modified by the proteins, as evidenced by comparison of complete membranes and derived liposomes, suggesting that the anthroyloxy probes were not in close contact with the proteins. An important change of the value of the mean rotational relaxation time as a function of the position of the anthroyl ring along the acyl chain was evidenced. In the complete membranes, a relatively more fluid medium was evidenced in the C₁₆ as compared to the C₂ region, while the rotational motion appeared to be the most hindered at the C₇–C₉ level. In the derived liposomes, a similar trend was observed but the mobility was higher at all levels. The decrease of the mean rotational relaxation time was more important for 12-AS and 16-AP. Temperature dependence of the mean rotational relaxation time of 2-AS, 12-AS and 16-AP in the complete membranes revealed the existence of a lipid reorganization occurring around 27°C and concerning mainly the C₁₆ region. The extent to which the acyl chain reacted to this perturbation at the C₁₂ level depended on pH. The presence of proteins increased the apparent magnitude of this reorganization and also modified the critical temperature from approx. 23°C in the derived liposomes to approx. 27°C in the complete membranes. Thermal dependence of the maximum velocity of the $\text{3-}\text{oxosteroid}\text{Δ}{}^5\text{?Δ}{}^4\text{-}\text{isomerase}$, the second enzyme in the enzymatic sequence, responsible for the biosynthesis of the $\text{3-}\text{oxo}\text{-Δ}{}^4\text{-}\text{steroids}$ in the adrenal cortex microsomes, was studied. The activation energy of the catalyzed reaction was found to be low and constant ($\text{2–5}\text{kcal}\text{·}\text{mol}{}^{\mathrm{?1}}$) in the temperature range 16–40°C at pH 7.5, 8.5 and 9, corresponding to the minimum, intermediate and maximum rate, respectively. A drastic increase of the activation energy ($\text{20}\text{kcal}\text{·}\text{mol}{}^{\mathrm{?1}}$) was observed at temperature below 16°C at pH 7.5. A correlated change of the $\text{p}\text{K}{}_{\mathrm{<mtext>ES</mtext>}}{}^{\mathrm{<mtext>app</mtext>}}$ as function of temperature was detected; at 36°C $\text{p}\text{K}{}_{\mathrm{<mtext>ES</mtext>}}{}^{\mathrm{<mtext>app</mtext>}}\text{= 8.3}$ while at 13°C the value shifted to 8.7. The pH range of the group ionization was narrower at 13°C. In contrast with the behaviour of the $\text{3β-}\text{hydroxy}\text{-Δ}{}^5\text{-}\text{steroid dehydrogenase}$, the $\text{3-}\text{oxosteroid}\text{Δ}{}^5\text{?Δ}{}^4\text{-}\text{isomerase}$ was apparently unaffected by the lipid reorganization at 27°C. It is suggested that this enzyme possesses a different and more fluid lipid environment than the bulk lipids.     

Purification and Functional Reconstitution of the Human CHIP28 Water Channel Expressed inSaccharomyces cerevisiae

The yeastSaccharomyces cerevisiaewas used for heterologous expression of the human CHIP28 water Aquaporin-1 channel (Aquaporin-1). A nine-amino-acid epitope of the influenza hemagglutinin protein (HA epitope), recognized by the monoclonal antibody 12CA5, was chosen to tag CHIP28 at its N-terminus. Epitope-tagged CHIP28 was purified from yeast extracts by immunochromatography on protein A/12CA5-coupled beads, after KI extraction and detergent solubilization, then concentrated by anion exchange chromatography. Purified protein was reconstituted in proteoliposomes and was shown to function as a water channel by stopped-flow spectrophotometry. This study demonstrates that the yeast has the capacity to produce functional aquaporins at levels sufficient for biochemical and biophysical analyses.     

Fungal‐host diversity among mycoheterotrophic plants increases proportionally to their fungal‐host overlap

The vast majority of plants obtain an important proportion of vital resources from soil through mycorrhizal fungi. Generally, this happens in exchange of photosynthetically fixed carbon, but occasionally the interaction is mycoheterotrophic, and plants obtain carbon from mycorrhizal fungi. This process results in an antagonistic interaction between mycoheterotrophic plants and their fungal hosts. Importantly, the fungal‐host diversity available for plants is restricted as mycoheterotrophic interactions often involve narrow lineages of fungal hosts. Unfortunately, little is known whether fungal‐host diversity may be additionally modulated by plant–plant interactions through shared hosts. Yet, this may have important implications for plant competition and coexistence. Here, we use DNA sequencing data to investigate the interaction patterns between mycoheterotrophic plants and arbuscular mycorrhizal fungi. We find no phylogenetic signal on the number of fungal hosts nor on the fungal hosts shared among mycoheterotrophic plants. However, we observe a potential trend toward increased phylogenetic diversity of fungal hosts among mycoheterotrophic plants with increasing overlap in their fungal hosts. While these patterns remain for groups of plants regardless of location, we do find higher levels of overlap and diversity among plants from the same location. These findings suggest that species coexistence cannot be fully understood without attention to the two sides of ecological interactions.     

High‐Throughput DNA sequencing of ancient wood

Reconstructing the colonization and demographic dynamics that gave rise to extant forests is essential to forecasts of forest responses to environmental changes. Classical approaches to map how population of trees changed through space and time largely rely on pollen distribution patterns, with only a limited number of studies exploiting DNA molecules preserved in wooden tree archaeological and subfossil remains. Here, we advance such analyses by applying high‐throughput (HTS) DNA sequencing to wood archaeological and subfossil material for the first time, using a comprehensive sample of 167 European white oak waterlogged remains spanning a large temporal (from 550 to 9,800 years) and geographical range across Europe. The successful characterization of the endogenous DNA and exogenous microbial DNA of 140 (~83%) samples helped the identification of environmental conditions favouring long‐term DNA preservation in wood remains, and started to unveil the first trends in the DNA decay process in wood material. Additionally, the maternally inherited chloroplast haplotypes of 21 samples from three periods of forest human‐induced use (Neolithic, Bronze Age and Middle Ages) were found to be consistent with those of modern populations growing in the same geographic areas. Our work paves the way for further studies aiming at using ancient DNA preserved in wood to reconstruct the micro‐evolutionary response of trees to climate change and human forest management.     

An inside job for siRNAs

Among the three main categories of small silencing RNAs in insects and mammals-siRNAs, miRNAs, and piRNAs-siRNAs were thought to arise primarily from exogenous sources, whereas miRNAs and piRNAs arise from endogenous loci. Recent work in flies and mice reveals several classes of endogenous siRNAs (endo-siRNAs) that contribute to functions previously reserved for miRNAs and piRNAs, including gene regulation and transposon suppression.     

Anaerobic Granular Sludge Bioreactor Technology

Anaerobic digestion is a mature wastewater treatment technology, with worldwide application. The predominantly applied bioreactor designs, such as the upflow anaerobic sludge blanket and expanded granular sludge bed, are based on the spontaneous formation of granular sludge. Despite the exploitation of granular reactors at full-scale for more than two decades, the mechanisms of granulation are not completely understood and numerous theories have been put forward to describe the process from a biological, ecological and engineering point of view. New technological opportunities are emerging for anaerobic digestion, aided by an improved understanding of microbiological and environmental factors affecting the formation and activity of anaerobic granular sludge.