The phylogenetic status of arthropods, as inferred from 18S rRNA sequences

Partial 18S rRNA sequences of five chelicerate arthropods plus a crustacean, myriapod, insect, chordate, echinoderm, annelid, and platyhelminth were compared. The sequence data were used to infer phylogeny by using a maximum-parsimony method, an evolutionary-distance method, and the evolutionary-parsimony method. The phylogenetic inferences generated by maximum-parsimony and distance methods support both monophyly of the Arthropoda and monophyly of the Chelicerata within the Arthropoda. These results are congruent with phylogenies based on rigorous cladistic analyses of morphological characters. Results support the inclusion of the Arthropoda within a spiralian or protostome coelomate clade that is the sister group of a deuterostome clade, refuting the hypothesis that the arthropods represent the "primitive" sister group of a protostome coelomate clade. Bootstrap analyses and consideration of all trees within 1% of the length of the most parsimonious tree suggest that relationships between the nonchelicerate arthropods and relationships within the chelicerate clade cannot be reliably inferred with the partial 18S rRNA sequence data. With the evolutionary-parsimony method, support for monophyly of the Arthropoda is found in the majority of the combinations analyzed if the coelomates are used as "outgroups." Monophyly of the Chelicerata is supported in most combinations assessed. Our analyses also indicate that the evolutionary-parsimony method, like distance and parsimony, may be biased by taxa with long branches. We suggest that a previous study's inference of the Arthropoda as paraphyletic may be the result of (a) having two few arthropod taxa available for analysis and (b) including long-branched taxa.      

Rating of perceived exertion as a tool for prescribing and self regulating interval training: a pilot study

The aim of the present study was to analyse the usefulness of the 6-20 rating of perceived exertion (RPE) scale for prescribing and self-regulating high-intensity interval training (HIT) in young individuals. Eight healthy young subjects (age = 27.5±6.7 years) performed maximal graded exercise testing to determine their maximal and reserve heart rate (HR). Subjects then performed two HIT sessions (20 min on a treadmill) prescribed and regulated by their HR (HR: 1 min at 50% alternated with 1 min at 85% of reserve HR) or RPE (RPE: 1 minute at the 9-11 level [very light-fairly light] alternated with 1 minute at the 15-17 level [hard-very hard]) in random order. HR response and walking/running speed during the 20 min of exercise were compared between sessions. No significant difference between sessions was observed in HR during low- (HR: 135±15 bpm; RPE: 138±20 bpm) and high-intensity intervals (HR: 168±15 bpm; RPE: 170±18 bpm). Walking/running speed during low- (HR: 5.7±1.2 km · h⁻¹; RPE: 5.7±1.3 km · h⁻¹) and high-intensity intervals (HR: 7.8±1.9 km · h⁻¹; RPE: 8.2±1.7 km · h⁻¹) was also not different between sessions. No significant differences were observed in HR response and walking/running speed between HIT sessions prescribed and regulated by HR or RPE. This finding suggests that the 6-20 RPE scale may be a useful tool for prescribing and self-regulating HIT in young subjects.     

ADP-ribosylation factor 1 and its activation of phospholipase D are important for the assembly of very low density lipoproteins

The role of ADP-ribosylation factor 1 (ARF-1) in the assembly of very low density lipoproteins (VLDL) was investigated by expressing dominant-negative mutants in McA-RH7777 cells. Transient expression of ARF-1(T31N), a GDP-restrictive mutant, significantly inhibited apolipoprotein B-100 (apoB-100) VLDL production without influencing the biosynthesis of apoB-100 low density lipoproteins or total apoB production (indicating that it inhibited the second step of VLDL assembly) and without altering total protein production or biosynthesis of transferrin, phosphatidylcholine, or triglycerides. These effects were confirmed in stable inducible transfectants. In contrast, expression of an ARF-1 mutant lacking the N-terminal 17 amino acids, which has no myristoylation site and cannot interact with the microsomal membrane, did not affect VLDL assembly. Thus, active ARF-1 is needed for the second step of the process. To further explore these observations, we developed a cell-free system based on the postnuclear supernatant isolated from McA-RH7777 cells. In this system, 10-15% of the apoB-100 pool was converted to VLDL in a time- and temperature-dependent way. The assembly process was highly dependent on a heat-stable factor in the d > 1.21 g/ml infranatant of fetal calf serum; this factor was not present in low density lipoproteins or VLDL. Brefeldin A inhibited VLDL assembly in this system, as did a synthetic peptide (corresponding to N-terminal amino acids 2-17 of ARF-1) that displaces ARF-1 from the membrane. Thus, active ARF-1 is also needed for cell-free assembly of VLDL. Guanosine 5'-3-O-(thio)triphosphate also inhibited VLDL assembly in this system, indicating that the process requires ongoing hydrolysis of GTP. 1-Butanol, which inhibits the formation of phosphatidic acid (PA) and instead gives rise to phosphatidylbutanol, inhibited VLDL assembly, whereas 2-butanol, which does not inhibit PA formation, failed to do so. Thus, phospholipase D (PLD)-catalyzed formation of PA from phosphatidylcholine is essential for VLDL assembly. In support of this conclusion, exogenous PLD prevented brefeldin A from inhibiting the assembly process. Our results indicate that ARF-1 participates in the second step of VLDL assembly through a process that involves activation of PLD and production of PA.     

Long-term organic-inorganic fertilization ensures great soil productivity and bacterial diversity after natural-to-agricultural ecosystem conversion

Natural ecosystems comprise the planet’s wild plant and animal resources, but large tracts of land have been converted to agroecosystems to support the demand for agricultural products. This conversion limits the number of plant species and decreases the soil biological diversity. Here we used high-throughput 16S rRNA gene sequencing to evaluate the responses of soil bacterial communities in long-term converted and fertilized red soils (a type of Ferralic Cambisol). We observed that soil bacterial diversity was strongly affected by different types of fertilization management. Oligotrophic bacterial taxa demonstrated large relative abundances in chemically fertilized soil, whereas copiotrophic bacterial taxa were found in large relative abundances in organically fertilized and fallow management soils. Only organic-inorganic fertilization exhibited the same local taxonomic and phylogenetic diversity as that of a natural ecosystem. However, the independent use of organic or inorganic fertilizer reduced local taxonomic and phylogenetic diversity and caused biotic homogenization. This study demonstrated that the homogenization of bacterial communities caused by natural-to-agricultural ecosystem conversion can be mitigated by employing rational organic-inorganic fertilization management.     

The genetic basis of anoxygenic photosynthetic arsenite oxidation

‘Photoarsenotrophy’, the use of arsenite as an electron donor for anoxygenic photosynthesis, is thought to be an ancient form of phototrophy along with the photosynthetic oxidation of Fe(II), H₂S, H₂ and . Photoarsenotrophy was recently identified from Paoha Island's (Mono Lake, CA) arsenic‐rich hot springs. The genomes of several photoarsenotrophs revealed a gene cluster, arxB2AB1CD, where arxA is predicted to encode for the sole arsenite oxidase. The role of arxA in photosynthetic arsenite oxidation was confirmed by disrupting the gene in a representative photoarsenotrophic bacterium, resulting in the loss of light‐dependent arsenite oxidation. In situ evidence of active photoarsenotrophic microbes was supported by arxA mRNA detection for the first time, in red‐pigmented microbial mats within the hot springs of Paoha Island. This work expands on the genetics for photosynthesis coupled to new electron donors and elaborates on known mechanisms for arsenic metabolism, thereby highlighting the complexities of arsenic biogeochemical cycling.     

Metabolic control analysis aimed at the ribose synthesis pathways of tumor cells: a new strategy for antitumor drug development

Metabolic control analysis predicts that effects on tumor growth are likely to be obtained with lower concentrations of drug, if an enzyme with a high control coefficient on tumor growth is being inhibited. Here we measure glucose-6-phosphate dehydrogenase (G6PDH) control coefficient on in vivo tumor growth using mice bearing Ehrlich ascites tumor cells. We used dehydroepiandrosterone-sulphate (DHEA-S), an uncompetitive inhibitor of this enzyme and the in situ cytochemical method to measure the enzyme activity changes that accompany changes on tumor cell growth. This method ensures that the enzyme activity determined is the one existing in the in situ conditions and enables computing a control coefficient in in situ conditions. From the data obtained on tumor cell number and the in situ enzyme activities in absence and presence of DHEA-S, a control coefficient of 0.41 for G6PDH on tumor cell growth was computed. This value is approximately the half of the transketolase control coefficient value of 0.9 previously reported. Moreover, the use of in situ methods to assess enzyme activities, applied for first time for the calculation of control coefficients in this study, opens new avenues to the use of uncompetitive inhibitors for the measurement of in situ control coefficients.