Multiple pathways for triacylglycerol biosynthesis in Streptomyces coelicolor

The terminal reaction in triacylglyceride (TAG) biosynthesis is the esterification of diacylglycerol (DAG) with a fatty acid molecule. To study this reaction in Streptomyces coelicolor, we analyzed three candidate genes (sco0958, sco1280, and sco0123) whose products significantly resemble the recently identified wax ester synthase/acyl-coenzyme A (CoA):DAG acyltransferase (DGAT) from Acinetobacter baylyi. The deletion of either sco0123 or sco1280 resulted in no detectable decrease in TAG accumulation. In contrast, the deletion of sco0958 produced a dramatic reduction in neutral lipid production, whereas the overexpression of this gene yielded a significant increase in de novo TAG biosynthesis. In vitro activity assays showed that Sco0958 mediates the esterification of DAG using long-chain acyl-CoAs (C(14) to C(18)) as acyl donors. The K(m) and V(max) values of this enzyme for myristoyl-CoA were 45 muM and 822 nmol mg(-1) min(-1), respectively. Significantly, the triple mutant strain was not completely devoid of storage lipids, indicating the existence of alternative TAG-biosynthetic routes. We present strong evidence demonstrating that the residual production of TAG in this mutant strain is mediated, at least in part, by an acyl-CoA-dependent pathway, since the triple mutant still exhibited DGAT activity. More importantly, there was substantial phospholipid:DGAT (PDAT) activity in the wild type and in the triple mutant. This is the first time that a PDAT activity has been reported for bacteria, highlighting the extreme metabolic diversity of this industrially important soil microorganism.     

Metabolomic and proteomic changes in the xylem sap of maize under drought

Plants produce compounds in roots that are transported to shoots via the xylem sap. Some of these compounds are vital for signalling and adaptation to environmental stress such as drought. In this study, we screened the xylem sap using mass spectrometry to quantify the changes in new and previously identified sap constituents under extended drought. We detected and quantified the changes in the concentration of 31 compounds present in the xylem sap under progressively increasing drought stress. We found changes in the hormones abscisic acid (ABA) and cytokinin, and the presence of high concentrations of the aromatic cytokinin 6-benzylaminopurine (BAP). Several phenylpropanoid compounds (coumaric, caffeic and ferulic acids) were found in xylem sap. The concentrations of some of these phenylpropanoid compounds changed under drought. In parallel, an analysis of the xylem sap proteome was conducted. We found a higher abundance of cationic peroxidases, which with the increase in phenylpropanoids may lead to a reduction in lignin biosynthesis in the xylem vessels and could induce cell wall stiffening. The application of new methodologies provides insights into the range of compounds in sap and how alterations in composition may lead to changes in development and signalling during adaptation to drought.     

Amyloid-cholinesterase interactions. Implications for Alzheimer's disease

Acetylcholinesterase is an enzyme associated with senile plaques. Biochemical studies have indicated that acetylcholinesterase induces amyloid fibril formation by interaction throughout the peripherical anionic site of the enzyme forming highly toxic acetylcholinesterase-amyloid-beta peptide (Abeta) complexes. The pro-aggregating acetylcholinesterase effect is associated with the intrinsic amyloidogenic properties of the corresponding Abeta peptide. The neurotoxicity induced by acetylcholinesterase-Abeta complexes is higher than the that induced by the Abeta peptide alone, both in vitro and in vivo. The fact that acetylcholinesterase accelerates amyloid formation and the effect is sensitive to peripherical anionic site blockers of the enzyme, suggests that specific and new acetylcholinesterase inhibitors may well provide an attractive possibility for treating Alzheimer's disease. Recent studies also indicate that acetylcholinesterase induces the aggregation of prion protein with a similar dependence on the peripherical anionic site.     

The outcome of phagocytic cell division with infectious cargo depends on single phagosome formation

Given that macrophages can proliferate and that certain microbes survive inside phagocytic cells, the question arises as to the post-mitotic distribution of microbial cargo. Using macrophage-like cells we evaluated the post-mitotic distribution of intracellular Cryptococcus yeasts and polystyrene beads by comparing experimental data to a stochastic model. For beads, the post-mitotic distribution was that expected from chance alone. However, for yeast cells the post-mitotic distribution was unequal, implying preferential sorting to one daughter cell. This mechanism for unequal distribution was phagosomal fusion, which effectively reduced the intracellular particle number. Hence, post-mitotic intracellular particle distribution is stochastic, unless microbial and/or host factors promote unequal distribution into daughter cells. In our system unequal cargo distribution appeared to benefit the microbe by promoting host cell exocytosis. Post-mitotic infectious cargo distribution is a new parameter to consider in the study of intracellular pathogens since it could potentially define the outcome of phagocytic-microbial interactions.     

Influence of type II 5′ deiodinase on TSH content in diabetic rats

The influence of hypothalamic and pituitary type II 5′ deiodinase (5′D-II) activities and T3 content on pituitary TSH content was investigated in streptozotocin (STZ)-induced diabetic rats (D). The results show, first, that hypothalamic and pituitary 5′D-II activities were lower in neonatal D rats versus control (C) rats, and the normal developmental pattern was altered. Secondly, when D and C rats were thyroidectomized (Tx) at 25 days of age (D+Tx, C+Tx), pituitary and hypothalamic 5′D-II activities increased ten days later in both populationsvs. intact rats, but the percentage of increase was smaller in D+Tx than in C+Tx. The hypothalamic T3 to T4 ratios were also decreased in D+Tx animals (0.38) as compared to C+Tx rats (1.64). The hypothalamic T3 content was reduced by 30% in D as compared to C rats and by 80% in D+Tx as compared to C+Tx rats, showing a defect in hypothalamic T4 deiodination. Pituitary TSH content increased after Tx in D+Tx, but not in C+Tx. These results in diabetic rats indicate that the hypothalamic and pituitary 5′D-II activity and hypothalamic T3 content are affected by diabetes and play a role in the regulation of pituitary TSH content.     

Gender difference in cardiovagal baroreflex gain in humans.

We tested the hypothesis that women would demonstrate lower cardiovagal baroreflex gain compared with men. If so, we further hypothesized that the lower cardiovagal baroreflex gain in women would be associated with their lower aerobic fitness and higher body fat percentage compared with men. To accomplish this, we measured cardiovagal baroreflex gain (modified Oxford technique) in sedentary, nonobese (body mass index < 25 kg/m2) men (age = 26.0 +/- 2.1 yr, n = 11) and women (age = 26.9 +/- 1.6 yr, n = 14). Resting R-R interval and diastolic blood pressure were similar in the two groups, but systolic blood pressure was lower (P < 0.05) in the women. Cardiovagal baroreflex gain was significantly lower in the women compared with the men (13.3 +/- 1.5 vs. 20.0 +/- 2.8 ms/mmHg, P < 0.05). The lower cardiovagal baroreflex gain in the women was not related (P > 0.05) to their lower aerobic fitness and was only marginally related to their higher body fat percentage (r = -0.34, P < 0.05). There were no gender differences in the threshold and saturation, operating range, or operating point (all P > 0.05), although the operating point fell significantly to left (i.e., at a lower systolic blood pressure) compared with men. Therefore, the findings of this study suggest that the gain of the cardiovagal baroreflex is reduced whereas other parameters were similar in women compared with men. The mechanisms responsible for the reduced cardiovagal baroreflex gain remain unclear.     

A novel method for estimating the strength of positive mating preference by similarity in the wild

Mating preference can be a driver of sexual selection and assortative mating and is, therefore, a key element in evolutionary dynamics. Positive mating preference by similarity is the tendency for the choosy individual to select a mate which possesses a similar variant of a trait. Such preference can be modelled using Gaussian‐like mathematical functions that describe the strength of preference, but such functions cannot be applied to empirical data collected from the field. As a result, traditionally, mating preference is indirectly estimated by the degree of assortative mating (using Pearson's correlation coefficient, r) in wild captured mating pairs. Unfortunately, r and similar coefficients are often biased due to the fact that different variants of a given trait are nonrandomly distributed in the wild, and pooling of mating pairs from such heterogeneous samples may lead to “false–positive” results, termed “the scale‐of‐choice effect” (SCE). Here we provide two new estimators of mating preference (C_rough and C_scaled) derived from Gaussian‐like functions which can be applied to empirical data. Computer simulations demonstrated that r coefficient showed robust estimations properties of mating preference but it was severely affected by SCE, C_rough showed reasonable estimation properties and it was little affected by SCE, while C_scaled showed the best properties at infinite sample sizes and it was not affected by SCE but failed at biological sample sizes. We recommend using C_rough combined with the r coefficient to infer mating preference in future empirical studies.     

Nitrogen-fixing rhizobial strains isolated from Desmodium incanum DC in Argentina: Phylogeny,biodiversity and symbiotic ability

Desmodium spp. are leguminous plants belonging to the tribe Desmodieae of the subfamily Papilionoideae. They are widely distributed in temperated and subtropical regions and are used as forage plants, for biological control, and in traditional folk medicine. The genus includes pioneer species that resist the xerothermic environment and grow in arid, barren sites. Desmodium species that form nitrogen-fixing symbiosis with rhizobia play an important role in sustainable agriculture. In Argentina, 23 native species of this genus have been found, including Desmodium incanum. In this study, a total of 64 D. incanum-nodulating rhizobia were obtained from root nodules of four Argentinean plant populations. Rhizobia showed different abiotic-stress tolerances and a remarkable genetic diversity using PCR fingerprinting, with more than 30 different amplification profiles. None of the isolates were found at more than one site, thus indicating a high level of rhizobial diversity associated with D. incanum in Argentinean soils. In selected isolates, 16S rDNA sequencing and whole-cell extract MALDI TOF analysis revealed the presence of isolates related to Bradyrhizobium elkanii, Bradyrhizobium japonicum, Bradyrhizobium yuanmingense, Bradyrhizobium liaoningense, Bradyrhizobium denitrificans and Rhizobium tropici species. In addition, the nodC gene studied in the selected isolates showed different allelic variants.Isolates were phenotypically characterized by assaying their growth under different abiotic stresses. Some of the local isolates were remarkably tolerant to high temperatures, extreme pH and salinity, which are all stressors commonly found in Argentinean soils. One of the isolates showed high tolerance to temperature and extreme pH, and produced higher aerial plant dry weights compared to other inoculated treatments. These results indicated that local isolates could be efficiently used for D. incanum inoculation.