Chitobiase of planktonic crustaceans from South Atlantic coast (Southern Brazil): Characterization and influence of abiotic parameters on enzyme activity

Chitobiase is one of the enzymes involved in chitin degradation in nature. It is produced and released by a variety of organisms from bacteria to fish. In crustaceans, it is associated with digestive function and acts on the epidermis during the molting process. In the present study, the influence of water pH, temperature and salinity on maximum chitobiase activity (MCA), as well as the enzyme affinity (Km) for a substrate, the methylumbelliferyl N-acetyl-ß-d-glucosaminide (MUFNAG) was evaluated in the copepod Acartia tonsa. Km values for chitobiases of other crustaceans from the Patos Lagoon estuary and Cassino Beach (Southern Brazil) were also determined. For A. tonsa, MCA was observed at pH 5-6 and 30-35 °C. The range of pH was quite similar to that reported for other aquatic organisms. However, the range of temperature was lower than that previously reported. For salinity, no previous studies have considered the influence of this parameter on MCA. For A. tonsa, MCA was observed in freshwater, showing a significant linear decrease with increasing salinity. Considering that maximum copepod survival and growth rates are observed between 15 and 25 ppt, these findings suggest that the observed enzyme activity in this range of salinity (68 to 47% of that measured in freshwater) is not a limiting factor for A. tonsa growth. However, the extremely decreased enzyme activity observed in salinity 30 ppt (33% of that measured in freshwater) suggests that chitobiase activity might be one of the limiting factor for copepod growth at 30 ppt salinity or higher. Km values (μM) determined for organisms evaluated in the present study (copepod A. tonsa = 20.77; mysid Metamysidopsis elongata atlantica = 14.67; nauplii barnacle Balanus improvisus = 18.19; decapod zoea = 14.30; decapod megalopa = 24.77) were lower than those reported for other crustaceans from Northern Hemisphere. Also, they were much lower than those of organisms from different taxonomic groups like bacteria and fungi, but much higher than in protozoans and dinoflagelates. These findings suggest that chitobiase might be differentially evolved in each specific group of organism, and even within different ontogenetic stages of the same species, for a better adaptation to cope with its respective environmental needs.     

Influence of moon phase on fish assemblages in estuarine mangrove tidal creeks

Significant differences in the composition of fish assemblages during different moon phases were detected in mangrove tidal creeks of the Goiana Estuary. The numbers of Zabaleta anchovy Anchovia clupeoides, Tarpon snook Centropomus pectinatus and Guavina Guavina guavina as well as at least 15 other species showed significant changes according to moon phase and were higher in terms of individuals (32%) and mass (34%) during the new moon.     

Molecular survey of Hepatozoon species in lizards from North Africa

The prevalence of Hepatozoon parasites in 460 lizards from North Africa was studied by amplification and sequencing of the 18S rRNA gene. The phylogenetic analysis of the 18S rRNA gene provides new insights into the phylogeny of these parasites with multiple genetically distinct lineages recovered. Parasite prevalence differed significantly between lacertid lizards and geckos. Our results show that there is limited host specificity and no clear relation to the geographical distribution of Hepatozoon parasites.     

Genotoxic effects of doxorubicin in cultured human lymphocytes with different glutathione S-transferase genotypes

Doxorubicin (Dox) is a widely used drug in oncology with a broad spectrum of interactions with various cellular components; therefore, it is likely to act through different mechanisms. In clinical practice there is inter-individual variability in cytotoxic drug response and in the occurrence of adverse reactions. Glutathione S-transferases (GSTM1, GSTT1 and GSTP1) are thought to be involved in the detoxification of endogenous and exogenous genotoxicants. The aim of this work is the assessment of a possible influence of polymorphisms in GSTs on the levels of genetic damage induced in vitro by Dox in cultured human lymphocytes. For this purpose, whole blood cultures from individuals with different genotypes for GSTM1, GSTT1 and GSTP1 were exposed to Dox and the cytokinesis-blocked micronucleus (CBMN) assay was used as the endpoint for chromosomal damage in the lymphocytes. Genotyping of GSTM1 and GSTT1 was carried out by multiplex PCR and the GSTP1-Ile105Val polymorphism was determined by PCR/RFLP. The total number of micronuclei present in 1000 binucleated cells and the frequency of micronucleated binucleated lymphocytes in the different individuals were analyzed considering the GSTM1, GSTT1 and GSTP1 genotypes. The results obtained suggest that GSTM1 and GSTT1 deletion polymorphisms do not modify significantly the genotoxic potential of Dox. However, the GSTP1 Ile105Val polymorphism was associated with an increase of micronucleated binucleated cells induced by Dox. Lymphocytes from homozygous individuals for the variant form (Val/Val) presented a significant increase in micronucleated binucleated cells (approximately 1.5-fold; p<0.05) when compared with individuals with at least one wild-type allele. These results suggest a possible role for GSTP1 on the modulation of the genotoxicity induced by Dox, which may be considered in cancer therapy.     

The structures of Thermoplasma volcanium phosphoribosyl pyrophosphate synthetase bound to ribose-5-phosphate and ATP analogs

Phosphoribosyl pyrophosphate (PRPP) synthetase catalyzes the transfer of the pyrophosphate group from ATP to ribose-5-phosphate (R5P) yielding PRPP and AMP. PRPP is an essential metabolite that plays a central role in cellular metabolism. The enzyme from a thermophilic archaeon Thermoplasma volcanium (Tv) was expressed in Escherichia coli, crystallized, and its X-ray molecular structure was determined in a complex with its substrate R5P and with substrate analogs β,γ-methylene ATP and ADP in two monoclinic crystal forms, P2₁. The β,γ-methylene ATP- and the ADP-bound binary structures were determined from crystals grown from ammonium sulfate solutions; these crystals diffracted to 1.8 Å and 1.5 Å resolutions, respectively. Crystals of the ternary complex with ADP-Mg²⁺ and R5P were grown from a polyethylene glycol solution in the absence of sulfate ions, and they diffracted to 1.8 Å resolution; the unit cell is approximately double the size of the unit cell of the crystals grown in the presence of sulfate. The Tv PRPP synthetase adopts two conformations, open and closed, at different stages in the catalytic cycle. The binding of substrates, R5P and ATP, occurs with PRPP synthetase in the open conformation, whereas catalysis presumably takes place with PRPP synthetase in the closed conformation. The Tv PRPP synthetase forms a biological dimer in contrast to the tetrameric or hexameric quaternary structures of the Methanocaldococcus jannaschii and Bacillus subtilis PRPP synthetases, respectively.     

Complete denture hygiene and nocturnal wearing habits among patients attending the Prosthodontic Department in a Dental University in Brazil

Gerodontology 2010; doi: 10.1111/j.1741‐2358.2010.00369.x Complete denture hygiene and nocturnal wearing habits among patients attending the Prosthodontic Department in a Dental University in Brazil Objective: The aim of this study was to evaluate the overnight wearing and cleaning habits of complete denture wearers. Background: Successful complete denture treatment can be achieved when the patients are motivated and aware of appropriate denture wear and hygiene. Materials and methods: A sample of 224 complete denture wearers (162 women) aged 37–89 years was studied. Inclusion criteria comprised edentulous subjects who had received their new complete dentures between 2000 and 2005 in the Dental Clinic of the Araçatuba and Araraquara Dental School, São Paulo State University. Ethical approval was sought and granted. Subjects were interviewed using questions related to overnight denture wearing and denture cleaning habits. Possible statistical relationships among some of items were analysed by the chi‐square test at 5% significance level. Results: Of the patients, 55.8% removed their dentures during the overnight period and 88% did this every day. Among them, 66.4% removed both dentures. Most of the patients used brushing with toothpaste (105 patients – 46.87%) as a cleaning method. More than a half of the subjects (63.4%) showed biofilm and calculus on their dentures. Conclusion: The patients need instructions and motivation concerning denture hygienic and denture removal overnight.     

GC-biased gene conversion and selection affect GC content in the Oryza genus (rice)

Base composition varies among and within eukaryote genomes. Although mutational bias and selection have initially been invoked, more recently GC-biased gene conversion (gBGC) has been proposed to play a central role in shaping nucleotide landscapes, especially in yeast, mammals, and birds. gBGC is a kind of meiotic drive in favor of G and C alleles, associated with recombination. Previous studies have also suggested that gBGC could be at work in grass genomes. However, these studies were carried on third codon positions that can undergo selection on codon usage. As most preferred codons end in G or C in grasses, gBGC and selection can be confounded. Here we investigated further the forces that might drive GC content evolution in the rice genus using both coding and noncoding sequences. We found that recombination rates correlate positively with equilibrium GC content and that selfing species (Oryza sativa and O. glaberrima) have significantly lower equilibrium GC content compared with more outcrossing species. As recombination is less efficient in selfing species, these results suggest that recombination drives GC content. We also detected a positive relationship between expression levels and GC content in third codon positions, suggesting that selection favors codons ending with G or C bases. However, the correlation between GC content and recombination cannot be explained by selection on codon usage alone as it was also observed in noncoding positions. Finally, analyses of polymorphism data ruled out the hypothesis that genomic variation in GC content is due to mutational processes. Our results suggest that both gBGC and selection on codon usage affect GC content in the Oryza genus and likely in other grass species.     

Fractionation of Eucalyptus grandis chips by dilute acid-catalysed steam explosion

Steam explosion of Eucalyptus grandis has been carried out under various pretreatment conditions (200-210 degrees C, 2-5 min) after impregnation of the wood chips with 0.087 and 0.175% (w/w) H2SO4. This study, arranged as a 2(3) factorial design, indicated that pretreatment temperature is the most critical variable affecting the yield of steam-treated fractions. Pretreatment of 0.175% (w/w) H2SO4-impregnated chips at 210 degrees C for 2 min was the best condition for hemicellulose recovery (mostly as xylose) in the water soluble fraction, reaching almost 70% of the corresponding xylose theoretical yield. By contrast, lower pretreatment temperatures of 200 degrees C were enough to yield steam-treated substrates from which a 90% cellulose conversion was obtained in 48 h, using low enzyme loadings of a Celluclast 1.5 1 plus Novozym 188 mixture (Novo Nordisk). Release of water-soluble chromophores was monitored by UV spectroscopy and their concentration increased with pretreatment severity. The yield of alkali-soluble lignin increased at higher levels of acid impregnation and pretreatment temperatures. Thermoanalysis of these lignin fractions indicated a pattern of lignin fragmentation towards greater pretreatment severities but lignin condensation prevailed at the most drastic pretreatment conditions.