Hélène Dubeau

Cytogenetic damage related to low levels of methyl mercury contamination in the Brazilian Amazon

The mercury rejected in the water system, from mining operations and lixiviation of soils after deforestation, is considered to be the main contributors to the contamination of the ecosystem in the Amazon Basin. The objectives of the present study were to examine cytogenetic functions in peripheral lymphocytes within a population living on the banks of the Tapajós River with respect to methylmercury (MeHg) contamination, using hair mercury as a biological indicator of exposure. Our investigation shows a clear relation between methylmercury contamination and cytogenetic damage in lymphocytes at levels well below 50 micrograms/gram, the level at which initial clinical signs and symptoms of mercury poisoning occur. The first apparent biological effect with increasing MeHg hair level was the impairment of lymphocyte proliferation measured as mitotic index (MI). The relation between mercury concentration in hair and MI suggests that this parameter, an indicator of changes in lymphocytes and their ability to respond to culture conditions, may be an early marker of cytotoxicity and genotoxicity in humans and should be taken into account in the preliminary evaluation of the risks to populations exposed in vivo. This is the first report showing clear cytotoxic effects of long-term exposure to MeHg. Although the results strongly suggest that, under the conditions examined here, MeHg is both a spindle poison and a clastogen, the biological significance of these observations are as yet unknown. A long-term follow-up of these subjects should be undertaken.

Biomarkers of DNA damage in marine mammals

Certain environmental contaminants found in marine mammals have been shown to cause DNA damage and cancer. The micronuclei (MN), sister chromatid exchange (SCE) and/or chromosome aberration (CA) assays were used to assess baseline (spontaneous) levels of DNA damage in blood lymphocytes of individuals of the relatively healthy and lightly contaminated Arctic beluga whale (Delphinapterus leucas), Sarasota Bay, FL, bottlenose dolphin (Tursiops truncatus) and Northwestern Atlantic grey (Halichoerus grypus) and harp (Phoca groenlandicus) seal populations. MN cell (MNC) frequencies ranged between 2 and 14/1000 binucleated (BN) cells and were statistically similar between species. In bottlenose dolphins, MNC frequency was correlated with age and was significantly higher in females than in males. No intraspecific variation in MNC frequency was found in beluga whales. Intraspecific variation was not tested in seals due to the small sample size. Frequencies of SCEs and total CAs, excluding gaps, ranged, respectively, between 1 and 15 SCE(s)/per cell and 4-6 CAs/100 cells in beluga whales. SCE and CA frequencies did not vary with age or sex in beluga whales. The MN, SCE and CA assays were found to be practical tools for the detection of DNA damage in marine mammals and could be used in the future to compare DNA damage between relatively lightly and highly contaminated populations.

Short chain fatty acid esters synthesis by commercial lipases in low-water systems and by resting microbial cells in aqueous medium

Thirteen commercial lipases in hexane and seventeen bacterial cell suspensions in aqueous media were screened for the production of ethyl valerate and ethyl butyrate. The highest esterifying activity was obtained with commercial Pancrealipase (Biozymes Inc.) and Candida rugosa lipase (Amano Enzyme Ltd) and with bacterial cell suspension from Pseudomonas fragi CRDA 446. Commercial enzymes gave molar conversion yield of 68% over 24 h as compared to 17% with whole cells in aqueous medium. However, a comparison of both sources of biocatalyst i.e. whole microbial cells and commercial lipases, based on the amount of ester produced per g of protein for a complete reaction, indicated similar activities.

Xylanase ofChaetomiumcellulolyticum: Its nature of production and hydrolytic potential

SummaryMaximum xylanase production byChaetomiumcellulolyticum was obtained in the culture supernatant after 30 h of growth at 37°C in basal medium containing 1% xylan at pH maintained between 6.5 and 7.5. Addition of 0.05% Tween 80 to the medium increased the enzyme production considerably. Xylanase production was found to be growth associated. The optimal conditions for enzymatic hydrolysis of xylan were found to be pH 6.0 and 50°C. During enzymatic hydrolysis, xylose, xylobiose and other xylooligosaccharides were liberated from xylan. The pH values for xylanase production and for xylan hydrolysis were closely related to the utilization of hemicelluloses of aspen wood for fungal protein production by this organism as reported in our earlier work.

Production of xylanases by Chaetomium cellulolyticum during growth on lignocelluloses.

SummaryChaetomiumcellulolyticum was able to produce xylanases on all the three lignocelluloses: wheat straw, corn stover and aspen wood. Wheat straw was the best. Solid state fermentation of lignocelluloses gave higher yields of xylanases than liquid state fermentation, but it took longer time of incubation.

PHYSICAL FACTORS INFLUENCING THE PRODUCTION OF STRAWBERRY AROMA BY PSEUDOMONAS FRAGI GROWN IN SKIM MILK

SummaryThe influence of temperature, agitation speed, pH and biomass on the synthesis of 19 metabolites contributing to a strawberry aroma was followed over a 72 h fermentation of skim milk byPseudomonasfragi. Amongst the major odor-active metabolites were ethyl butyrate, ethyl hexanoate, ethyl 2-hexenoate, ethyl crotonate, ethyl isovalerate and ethyl 2-methyl hexanoate. Up to 17 ppm of some of these metabolites were detected at 60 h of fermentation, approximately 36 h after the beginning of the stationary growth phase. The production of most odor-active metabolites was higher at 11°C and 150 RPM than at 15, 20 or 25°C and 200 or 250 RPM. The development of off-aromas was observed at high temperatures and at high agitation speeds.

Effects of lymphocyte subpopulations on the clonal assay of HPRT mutants: occupational exposure to cytostatic drugs.

The mutagenic effect of occupational exposure to antineoplastic agents was studied in chemotherapy nurses and pharmacists using the T-lymphocyte clonal assay. A significant increase in mutant frequency was observed compared to controls. However, in the present study, cloning efficiency without selection (CEU) was significantly reduced in exposed personnel raising the possibility of an overestimation of the calculated MF. Changes in lymphocyte populations and clonal potential of T-cells were also observed following exposure. CEU was related to % CD4 cells but CE with selection (CETG) was not. Differences in clonal ability of T-cells under selective and unselective conditions coupled with differential lethal effect of antineoplastic agents on lymphocyte subsets may result in inaccurate estimation of MF.