Independent and combined cytotoxicity and genotoxicity of triethylene glycol dimethacrylate and urethane dimethacrylate

Dental composite materials contain polymers of methacrylates, which, due to mechanical abrasion and enzymatic action of saliva, may release their monomers into oral cavity and the pulp. Moreover, polymerization is always incomplete and leaves usually considerable fraction of free monomers. Mechanisms of the genotoxicity of methacrylate monomers have been rarely explored. As the polymerization of a monomer is catalyzed by a co-monomer, their combined action should be considered. In the present work, we investigated cytotoxic and genotoxic effects of urethane dimethacrylate (UDMA), often used as a monomer, at 1 mM, and triethylene glycol dimethacrylate (TEGDMA), a typical co-monomer, at 5 mM singly and in combination. Experiments were conducted on Chinese hamster ovary cells. Cell viability, apoptosis and cell cycle were assessed by flow cytometry, whereas DNA damage was evaluated by plasmid conformation test and comet assay. Both compounds decreased the viability of the cells, but did not induce strand breaks in an isolated plasmid DNA. However, both substances, either singly or in combination, damaged DNA in CHO cells as evaluated by comet assay. Both compounds induced apoptosis, but a combined action of them led to a decrease in the number of apoptotic cells. The combined action of UDMA and TEGDMA in the disturbance of cell cycle was lesser compared to the action of each compound individually. Individually, though UDMA and TEGDMA may induce cytotoxic and genotoxic, however, a combination of both does not produce a significant increase in these effects.     

Enzyme synthesis of oligosaccharides using cashew apple juice as substrate

The use of agriculture substrates in industrial biotechnological processes has been increasing because of their low cost. In this work, the use of clarified cashew apple juice was investigated as substrate for enzyme synthesis of prebiotic oligosaccharide. The results showed that cashew apple juice is a good source of reducing sugars and can be used as substrate for the production of dextransucrase by Leuconostoc citreum B-742 for the synthesis of oligosaccharides using the crude enzyme. Optimal oligosaccharide yield (approximately 80%) was obtained for sucrose concentrations lower than 60 g/L and reducing sugar concentrations higher than 100 g/L.     

Ligninolytic activity of tropical rainforest basidiomycetes

A total of 116 strains of Brazilian tropical rainforest basidiomycetes were evaluated in terms of their ability to oxidize the dye rhemazol brilliant blue R (RBBR) and guaiacol. Laccase and peroxidase activities were detected by the drop test using solutions of α-naphthol and pyrogallol, respectively. RBBR and guaiacol oxidation occurred in 96.6 and 87.1% of the strains tested, respectively. One hundred strains oxidized both substrates. In the drop test, most strains presented laccase (96.6%) and peroxidase (92.2%) activity. The quick screening method used here can be useful to identify ligninolytic fungal strains to be used in various biotechnological applications. This revised version was published online in November 2006 with corrections to the Cover Date.     

The spatial organization of the active sites of the bifunctional oligomeric enzyme tryptophan synthase: Cross-linking by a novel method

To achieve specific cross-linking between the active sites of the non-identical subunits tryptophan synthase from E. coli was modified by a novel method. After reaction with bifunctional reagents of the isolated subunits at their active sites, the tetrameric complex was formed and the free ends of the reagent molecules reacted with each other forming a covalent bridge between the subunits. The distance between the amino acid side chains involved in the cross-linking should not exceed approx. 1.8 nm. A distance much shorter than that is unlikely since all attempts to cross-link the active sites with different shorter bifunctional reagents failed. The implications of these results in the mechanism of action of the enzyme are discussed.     

Population structure of North Atlantic and North Pacific sei whales (<Emphasis Type="Italic">Balaenoptera borealis</Emphasis>) inferred from mitochondrial control region DNA sequences and microsatellite genotypes

Currently, three stocks of sei whales (Balaenoptera borealis) are defined in the North Atlantic; the Nova Scotian, Iceland-Denmark Strait and Eastern North Atlantic stocks, which are mainly based upon historical catch and sighting data. We analyzed mitochondrial control region DNA (mtDNA) sequences and genotypes from 7 to 11 microsatellite loci in 87 samples from three sites in the North Atlantic; Iceland, the Gulf of Maine and the Azores, and compared against the North Pacific using 489 previously published samples. No statistically significant deviations from homogeneity were detected among the North Atlantic samples at mtDNA or microsatellite loci. The genealogy estimated from the mtDNA sequences revealed a clear division of the haplotypes into a North Atlantic and a North Pacific clade, with the exception of one haplotype detected in a single sample from the Azores, which was included in the North Pacific clade. Significant genetic divergence between the North Atlantic and North Pacific Oceans was detected (mtDNA Φ_ST?=?0.72, microsatellite Weir and Cockerham’s ? = 0.20; p?<?0.001). The coalescent-based estimate of the population divergence time between the North Atlantic and North Pacific populations from the sequence variation among the mtDNA sequences was at 163,000 years ago. However, the inference was limited by an absence of samples from the Southern Hemisphere and uncertainty regarding mutation rates and generation times. The estimates of inter-oceanic migration rates were low (Nm at 0.007 into the North Pacific and at 0.248 in the opposite direction). Although estimates of genetic divergence among the current North Atlantic stocks were low and consistent with the extensive range of movement observed in satellite tagged sei whales, the high uncertainty of the genetic divergence estimates precludes rejection of multiple stocks in the North Atlantic.     

Exploring the low-pressure growth limit: evolution of Bacillus subtilis in the laboratory to enhanced growth at 5 kilopascals

Growth of Bacillus subtilis cells, normally adapted at Earth-normal atmospheric pressure (～101.3 kPa), was progressively inhibited by lowering of pressure in liquid LB medium until growth essentially ceased at 2.5 kPa. Growth inhibition was immediately reversible upon return to 101.3 kPa, albeit at a slower rate. A population of B. subtilis cells was cultivated at the near-inhibitory pressure of 5 kPa for 1,000 generations, where a stepwise increase in growth was observed, as measured by the turbidity of 24-h cultures. An isolate from the 1,000-generation population was obtained that showed an increase in fitness at 5 kPa when compared to the ancestral strain or a strain obtained from a parallel population that evolved for 1,000 generations at 101.3 kPa. The results from this preliminary study have implications for understanding the ability of terrestrial microbes to grow in low-pressure environments such as Mars.