Effect of mixing on biogas production during mesophilic anaerobic digestion of screened dairy manure in a pilot plant

The effect of mixing on biogas production of a 1.5‐m³ pilot continuous stirred tank reactor (CSTR) processing screened dairy manure was evaluated. Mixing was carried out by recirculation of reactor content with a mono pump. The experiment was conducted at a controlled temperature of 37±1°C and hydraulic retention times (HRTs) of 20 and 10 days. The effect of continuous and intermittent operation of the recirculation pump on biogas production was studied. At 10 days of HRT, the results showed a minimal influence of recirculation rate on biogas production and that continuous recirculation did not improve reactor performance. At 20 days of HRT, the recirculation rate did not affect reactor performance. Combination of low solid content in feed animal slurry and long HRTs results in minimal mixing requirements for anaerobic digestion.     

Zell- und stoffwechselphysiologische Untersuchungen an der Wurzel von Lemna minor L. unter besonderer Berücksichtigung von Kalium- und Kalziummangel

Ohne ZusammenfassungMit 12 Textabbildungen.Im Auszug vorgetragen auf der Botanikertagung Kassel 1949.     

Endocytosis in Trypanosoma cruzi (Euglenozoa: Kinetoplastea) epimastigotes: Visualization of ingested transferrin-gold nanoparticle complexes by confocal laser microscopy

Here we describe the visualization by confocal microscopy of ingested gold (15nm)-labeled transferrin in epimastigote forms of the protozoan Trypanosoma cruzi. Intracellular gold labeling was evident at two sites, which represent the bottom of the cytopharynx and the reservosomes. The gold tracer was best observed by confocal microscopy by using the 633nm excitation wavelength. Intracellular gold clusters larger than 60nm could be visualized by either gold reflection (light scattering) or photoluminescence modes. The gold reflection mode, the gold photoluminescence mode and the anti-transferrin immunofluorescence image of gold-labeled transferrin showed co-localization, thus demonstrating that the gold visualization modes did not represent artifacts or mislocalization of the biomarker. Visualization of protein-gold nanoparticle complexes by confocal microscopy thus emerges as a promising imaging tool to explore the endocytic pathway in trypanosomes and other cell types, as well as to perform immunolocalization studies using gold-labeled secondary antibodies.     

Co-fermentation of xylose and cellobiose by an engineered Saccharomyces cerevisiae

We have integrated and coordinately expressed in Saccharomyces cerevisiae a xylose isomerase and cellobiose phosphorylase from Ruminococcus flavefaciens that enables fermentation of glucose, xylose, and cellobiose under completely anaerobic conditions. The native xylose isomerase was active in cell-free extracts from yeast transformants containing a single integrated copy of the gene. We improved the activity of the enzyme and its affinity for xylose by modifications to the 5′-end of the gene, site-directed mutagenesis, and codon optimization. The improved enzyme, designated RfCO*, demonstrated a 4.8-fold increase in activity compared to the native xylose isomerase, with a K_m for xylose of 66.7?mM and a specific activity of 1.41?μmol/min/mg. In comparison, the native xylose isomerase was found to have a K_m for xylose of 117.1?mM and a specific activity of 0.29?μmol/min/mg. The coordinate over-expression of RfCO* along with cellobiose phosphorylase, cellobiose transporters, the endogenous genes GAL2 and XKS1, and disruption of the native PHO13 and GRE3 genes allowed the fermentation of glucose, xylose, and cellobiose under completely anaerobic conditions. Interestingly, this strain was unable to utilize xylose or cellobiose as a sole carbon source for growth under anaerobic conditions, thus minimizing yield loss to biomass formation and maximizing ethanol yield during their fermentation.     

Presence of α-amylase inhibitor in some members of the subtribe Phaseolinae (Phaseoleae: Fabaceae)

The presence of α-amylase inhibitor (αAI), phytohemagglutinin (PHA), and phaseolin was determined by immunochemical and biochemical methods in different members of the subtribe Phaseolinae (Phaseoleae: Fabaceae). Active αAI was present in taxa from the Phaseolus vulgaris–P. coccineus complex (P. vulgaris, P. coccineus, and P. polyanthus), as well as in P. acutifolius in accordance with previous molecular data separating these groups of species from others in the genus. All other Phaseolus species tested lacked α-amylase inhibitory activity, although some of them had immunoreactive polypeptides. αAI was found to be a polymorphic trait among wild and cultivated accessions of P. vulgaris, P. coccineus, and P. acutifolius. The presence of αAI is not exclusive of the genus Phaseolus as one of the Vigna species sampled, V. linearis, also contained α-amylase inhibitory activity.     

A theoretical and comparative CNDO study of chlorophylls a and b and their beryllium homologs

CNDO/II calculations of chlorophylls a and b and their beryllium homologs show that the 3d atomic orbitals of the metal atoms contribute significantly to the σ and π bonding energies. In both chlorophylls a and b replacement of magnesium by beryllium stabilizes the total molecular energy by 40 kcal/mol.