Efficient production of L‐lactic acid by Crabtree‐negative yeast Candida boidinii

Industrial production of L ‐lactic acid, which in polymerized form as poly‐lactic acid is widely used as a biodegradable plastic, has been attracting world‐wide attention. By genetic engineering we constructed a strain of the Crabtree‐negative yeast Candida boidinii that efficiently produced a large amount of L ‐lactic acid. The alcohol fermentation pathway of C. boidinii was altered by disruption of the PDC1 gene encoding pyruvate decarboxylase, resulting in an ethanol production that was reduced to 17% of the wild‐type strain. The alcohol fermentation pathway of the PDC1 deletion strain was then successfully utilized for the synthesis of L ‐lactic acid by placing the bovine L ‐lactate dehydrogenase‐encoding gene under the control of the PDC1 promoter by targeted integration. Optimizing the conditions for batch culture in a 5 l jar‐fermenter resulted in an L ‐lactic acid production reaching 85.9 g/l within 48 h. This productivity (1.79 g/l/h) is the highest thus far reported for L ‐lactic acid‐producing yeasts. DDBJ/EMBL/GenBank nucleotide database with Accession Nos. AB440630 and AB440631. Copyright © 2009 John Wiley & Sons, Ltd.     

Catalytic action of metallic salts in autoxidation and polymerization: 11. Polymerization of methacrylic acid esters with sodium hexanitrocobaltate in methanol-water

The polymerization of a series of methacrylic acid esters (methyl, ethyl, isopropyl and n-butyl) with sodium hexanitrocobaltate, Na₃[Co(NO₂)₆] was carried out in a methanol-water mixed solvent. The homogeneity of the polymerization system was dependent on the composition of the mixed solvent and greatly affected the rate of the polymerization. A maximum rate was obtained at approximately equimolar fractions of methanol and water in the polymerization of methyl methacrylate. The effect of bulkiness of ester groups on the polymerizability of each monomer was indistinguishable in the mixed solvent system. Kinetic study of the polymerization of methyl methacrylate in a mixed solvent of about an equimolar fraction of methanol and water gave the following polymerization equation: $\text{R}{}_{\mathrm{p}}\text{= k[l]}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{[}\text{M}\text{]}{}^2$, and an apparent activation energy of 10.6 kcal/mol. The copolymerization of methyl methacrylate and styrene with the initiator suggested that polymerization proceeded via a radical mechanism. The possibility of a certain interaction between initiator, solvent and monomer in the initial stage of the polymerization is discussed on the basis of the kinetic data, properties of oligomers of methyl methacrylate, spectroscopic and other data.     

Effect of water-Insoluble Powder Addition on Physical Properties of Gelatin Gel

Water-insoluble powder is often dispersed in shells of commercial soft capsules for various reasons, but little reports have been published about the effect of powder addition on the physical properties of the gelatin gel. Glass powder, titanium oxide, calcium carbonate and γ-orizanol were used as model of powder. Changes of Young modulus obtained from the tensile test showed that any powder addition to the gelatin sheet made the gelatin sheet hard not by the surface effect of powder but by the volumetric effect of it. In this test, any powders had no effect on the tensile strength of the gelatin sheet because there was little interaction between each powder and the gelatin gel in the break point. The limiting strain was decreased a little up to the specific amount of each powder and then beyond the specific amount that decreased steeply in the case of glass powder and γ-orizanol. There might be a suitable range of the amount of powder for the gelatin sheet to keep the plastic flow similar to the gelatin sheet containing no powder. In this work, it was shown that the physical properties of the gelatin shell would be regulated by powder addition to the gelatin sheet.     

Effect of polymer matrices on magnetic properties of plastic magnets

Plastic magnets were prepared using commercial polyamide (Nylon 12), polystyrene and ethylene-vinylacetate copolymer, and three kinds of ferrite magnetic powders with different concentration levels (20, 35 and 50 vol%). Their magnetic properties and thermal stability are discussed comparing viscoelasticity and thermal properties of the polymers and plastic magnets. Magnetic properties of the anisotropic plastic magnets were largely dependent on the concentration of the magnetic powder and its degree of orientation in the matrix. The degree of the orientation was mainly affected by the interaction between polymer matrix and magnetic powder, and viscoelastic property of the matrix polymer. It was also affected to some extent by the shape of the magnetic particles. The order of the interaction of the polymers to the magnetic powders was as follows: PA > EVA copolymer > PS, and PA-bonded magnets gave the highest magnetic properties among the matrices examined. The decrease in magnetic properties due to the change in the orientation of magnetic powder rarely occurred during thermal treatment.     

Regulation of tissue plasminogen activator production in cultured human fetal mesangial cells

This study was designed to determine the persistence of culturable bacteria versus DNA in the presence of a middle ear effusion in a chinchilla model of otitis media. Cohorts of animals were either infected with an ampicillin-resistant Haemophilus influenzae strain or injected with a tripartite inoculum consisting of freeze-thawed Streptococcus pneumoniae; pasteurized Moraxella catarrhalis; and DNA from H influenzae. The H influenzae-infected animals displayed culture positivity and polymerase chain reaction positivity through day 35. In the chinchillas infected with the low-copy number inocula of S pneumoniae, DNA was not detectable after day 1 from the co-inoculated pasteurized M catarrhalis bacteria or the purified H influenzae DNA; however, amplifiable DNA from the live low-copy number bacteria persisted through day 21 even though they were not culture-positive past day 3. These results demonstrate that DNA, and DNA from intact but nonviable bacteria, does not persist in an amplifiable form for more than a day in the presence of an effusion; however, live bacteria, while not culturable, persist in a viable state for weeks.     

Effects of ACE inhibitor on renal anemia in predialysis patients

Enterocolitis necroticans or pigbel is a rare condition characteristically affecting chronically malnourished people who abruptly increase their intake of protein. The classic presentation of the disease as seen in the highlands of Papua New Guinea is that of a necrotising enterocolitis after the ritual ingestion of contaminated pork. In this context, the presentation of the same disease in a well nourished white vegetarian in Oxford was all the more intriguing.     

In situ high temperature TEM observation of interaction between multi-walled carbon nanotube and in situ deposited gold nano-particles

Interaction between multi-walled carbon nanotubes (MWNTs) and deposited gold nano-particles has been dynamically observed in a 200 kV transmission electron microscope (TEM) using a specimen heating holder. Gold particles with diameters of several tens of microns were mixed with MWNTs to mount on the heating element of a specimen heating holder. The gold particles were instantaneously heated to 1373 K to deposit gold nano-particles on the MWNTs from a very short distance. The MWNTs were then heated to 1073 K to observe interaction between the deposited gold nano-particles and MWNTs. Some gold nano-particles drilled through the wall of the MWNT and entered the capillary space of the MWNTs. To characterize the mechanism of the transition of the gold nano-particles into the capillary space of the MWNT, high resolution TEM observation of the deformed wall of MWNT was also carried out.     

The nuclear actin-related protein Act3p/Arp4p is involved in the dynamics of chromatin-modulating complexes

Chromatin remodelling and histone-modifying complexes govern the modulation of chromatin structure. While components of these complexes are diverse, nuclear actin-related proteins (Arps) have been repeatedly found in these complexes from yeast to mammals. In most cases, Arps are required for functioning of the complexes, but the molecular mechanisms of nuclear Arps have as yet been largely unknown. The Arps and actin, sharing a common ancestor, are supposed to be highly similar in the three-dimensional structure of their core regions, including the ATP-binding pocket. The Arp Act3p/Arp4p of Saccharomyces cerevisiae exists within the nucleus, partly as a component of several high molecular mass complexes, including the NuA4 histone acetyltransferase (HAT) complex, and partly as uncomplexed molecules. We observed that mutations in the putative ATP-binding pocket of Act3p/Arp4p increased its concentration in the high molecular mass complexes and, conversely, that an excess of ATP or ATPgammaS led to the release of wild-type Act3p/Arp4p from the complexes. These results suggest a requirement of ATP binding by Act3p/Arp4p for its dissociation from the complexes. In accordance, a mutation in the putative ATP binding site of Act3p/Arp4p inhibited the conversion of the NuA4 complex into the smaller piccoloNuA4, which does not contain Act3p/Arp4p and exhibits HAT activity distinct from that of NuA4. Although the in vitro binding activity of ATP by recombinant Act3p/Arp4p was found to be rather weak, our observations, taken together, suggest that the ATP-binding pocket of Act3p/Arp4p is involved in the function of chromatin modulating complexes by regulating their dynamics.     

Bioinformatic Prediction of an tRNASec Gene Nested inside an Elongation Factor SelB Gene in Alphaproteobacteria

In bacteria, selenocysteine (Sec) is incorporated into proteins via the recoding of a particular codon, the UGA stop codon in most cases. Sec-tRNA^Sec is delivered to the ribosome by the Sec-dedicated elongation factor SelB that also recognizes a Sec-insertion sequence element following the codon on the mRNA. Since the excess of SelB may lead to sequestration of Sec-tRNA^Sec under selenium deficiency or oxidative stress, the expression levels of SelB and tRNA^Sec should be regulated. In this bioinformatic study, I analyzed the Rhizobiales SelB species because they were annotated to have a non-canonical C-terminal extension. I found that the open reading frame (ORF) of diverse Alphaproteobacteria selB genes includes an entire tRNA^Sec sequence (selC) and overlaps with the start codon of the downstream ORF. A remnant tRNA^Sec sequence was found in the Sinorhizobium meliloti selB genes whose products have a shorter C-terminal extension. Similar overlapping traits were found in Gammaproteobacteria and Nitrospirae. I hypothesized that once the tRNA^Sec moiety is folded and processed, the expression of the full-length SelB may be repressed. This is the first report on a nested tRNA gene inside a protein ORF in bacteria.