Thomas Njiné

Helium and carbon fluxes in Lake Nyos, Cameroon: constraint on next gas burst

On 21 August, 1986, a lethal gas burst issued from Lake Nyos in Cameroon, western Africa, killing at least 1700 people. Although the consensus is that the victims died of asphyxiation by CO2 of magmatic origin, the frequency of such catastrophic degassing events is still unknown. The CO2 flux at the bottom of Lake Nyos is estimated based on the measurement of3He4He and4He20Ne ratios and the chemical composition of gases exsolved from the lake water. The calculated CO2 flux at the bottom of Lake Nyos is(4.4 ± 2.3) × 1013cm3STP/year. Combined with the estimated release in the August 1986 event of (8 ± 2) × 1014 cm3 STP, the CO2 flux suggests that the gas burst may happen about once in18 ± 10 years, although the significant uncertainty should be taken into account for the frequency resulting from assumptions such as steady-state fluxes in the lake and small fractionization of the C/He ratio during the degassing event. Several yearly measurements of hypolimnetic fluxes and seasonal measurements of epilimnetic fluxes are needed to constrain better the recurrence interval. In addition, the results of a regional3He4He survey of carbonated mineral springs in northwestern Cameroon are discussed in the context of the regional geotectonics.

Survival and Growth of Vibrio cholerae, Escherichia coli, and Salmonella Spp. in Well Water Used for Drinking Purposes in Garoua (North Cameroon)

The ability of strains of faecal bacteria (Vibrio cholerae, Escherichia coli ATCC 25922, and four strains of Salmonella isolated, resp., from well water, pig, poultry, and human urine in Garoua) to survive or grow in well water microcosms was compared. Water samples were obtained from two wells in Garoua (north Cameroun). Autoclaving at 121°C for 15 min and filtration through 0.2 µm filter were used to make microcosms. Microcosms were constituted of unfiltered-autoclaved, filtered-nonautoclaved, and filtered-autoclaved well waters. Bacterial strains were inoculated at initial cell concentration of 3 Log10CFU/mL. All strains were able to survive/grow in used microcosms, and a maximal concentration of 5.61 Log10CFU/mL was observed. Survival abilities were strain and microcosm dependent. The declines were more pronounced in filtered-nonautoclaved water than in the other microcosms. E. coli and Salmonella sp. (poultry strain) lowered to undetectable levels (<1 Log10CFU/mL) after two days of water storage. V. cholera decreased over time, but surviving cells persisted for longer period in filtered-nonautoclaved water from well W1 (1.91 Log10CFU/mL) and well W2 (2.09 Log10CFU/mL). Competition for nutrients and/or thermolabile antimicrobial substances synthesized by “ultramicrocells” or by the autochthonous bacteria retained by the filter might affect the bacterial survival.

Involvement of cell shape and flagella in the bacterial retention during percolation of contaminated water through soil columns in tropical region.

Microorganisms’ retention in soil contributes to the natural purification of groundwater. Bacteria found in groundwater are generally of various shapes. The aim of this study was to assess the importance of cell shape and flagella in bacterial retention during polluted water percolation through two soil columns CA and CB, in the equatorial region in Central Africa. Percolation tests were carried out using different water loads samples which were contaminated by Escherichia coli (straight rods, peritrichous flagella), Vibrio parahaemolyticus (rods bacteria, polar flagella), and Staphylococcus saprophyticus (spherical, free-flagellum). It has been noted that showed that through soil column CA, the mean values of cells retention ratios (TR ) varied with bacteria species considered, and from one applied water load sample to another. E. coli T R and that of S. saprophyticus were not significantly different (P> 0.05) for the two soil columns. V. parahaemolyticus TR significantly differed from that of E. coli and S. saprophyticus through soil column CA (P< 0.01) when the highest water load was applied, and through soil column CB (P< 0.05) for each of water load applied. A relative hierarchical arrangement of retained cells based on the TR showed that V. parahaemolyticus was less retained through the 2 soil columns. S. saprophyticus in most cases was more retained than others. The physical properties of the bacterial cell must be taken into consideration when evaluating the transfer of bacteriological pollutants towards groundwater.

A morphological and ultrastructural study of Kozloffia catenula de Puytorac, 1968 (Ciliophora, Hysterocinetidae)

Summary The morphological study of Kozloffia catenula from silver impregnations brings new details on the sucker (presence of cytoskeletal fibers, absence of fragments of kineties) and the first description of the buccal infraciliature. Ultra-structural observations confirm that the latter is similar to that of Preptychostomum , with a paroral (stichodyad) and 3 adorai organelles. The second adorai organelle is segmented in two parts (AD2, AD2′). AD1, AD2 and AD2′ have 2 rows and AD3 only 1 row of ciliated kinetosomes. In the somatic cortex, the arrangement of the somatic kinetid confirms the existence of a particular hysterocinetian type of monokinetid. In the subclass Hysterocinetia, Kozloffia must be placed in the family Hysterocinetidae, clearly separated from the family Paraptychostomatidae.

Assessment of the hierarchical involvement of chemical characteristics of soil layer particles during bacterial retention in Central Africa

The main purpose of this investigation was to rank, in hierarchical order, some soil chemical factors that impact the sorption parameters of fecal indicator bacteria and Salmonella sp, during their transfer from soil surface to the groundwater table. Sorption coefficients (Kf) and linearity exponents (Ϫ) were obtained using the Freundlich isotherm. When Salmonella sp was present alone, the values of Kf varied from 2.70 log units mg−1 to 7.84 log units mg−1 of soil, and Ϫ varied from 0.04 to 2.70. When the two fecal indicator bacteria were present, Kf varied from 0.48 log units mg−1 to 8.53 log units mg−1 of soil, and Ϫ varied from 0.06 to 1.19. When fecal indicator bacteria and Salmonella sp were mixed, Kf varied from 1.73 log units mg−1 to 7.70 log units mg−1 of soil, and Ϫ varied from 0.09 to 0.88. The predominant factors controlling each sorption parameter varied with respect to soil layer and the bacterial species involved.

Photoinactivation of Staphylococcus aureus and Vibrio parahaemolyticus in the model aquatic microcosm: effect of light intensity and dissolved biodegradable organic compound

The impact of light (1,000 × 100,000 lx) on the inactivation of S. aureus and V. parahaemolyticus has been assessed under different concentrations of dissolved biodegradable organic compound (BOC) at pH 7.0. First, a gradual decrease in the number of cultivable cells was observed. Secondly, a cell reactivation was observed and it was marked in the absence of BOC. In the absence of BOC, the lowest value of cell inhibition rate (CIR) during the first 3 h was 0.138 h(-1) for S. aureus and 0.218 h(-1) for V. parahaemolyticus. In the presence of 10,100 and 1,000 mg/l of BOC, it was 0.196 h(-1), 0.243 h(-1) and 0.257 h(-1) for S. aureus respectively, and 0.285 h(-1), 0.306 h(-1) and 0.409 h(-1) for V. parahaemolyticus respectively. The CIRs values of each bacterial species significantly varied (P<0.001) with the changes in BOC concentration. In most cases, no significant difference was noted in the CIRs of both species when they were under the same light intensity and BOC. Nevertheless, it seems important to consider the impact of dissolved BOC during the treatment of bacterial polluted water.

Contribution to the Study of Antibiotic Resistance on Salmonella and Shigella Strains Isolated in Central African Republic

Peoples are contaminated by germs such as Salmonella and Shigella. This contamination can occur either from the environment or by contact with infected animals on the farm. Peoples are frequently infected by the consumption of raw or undercooked meat, contaminated during the slaughter process [24]. Salmonella and Shigella are the leading cause of gastroenteritis food borne humans cause symptoms of a wide range of severity, usually manifested by a more or less severe diarrhea sometimes requiring therapeutic management [5-8]. In the absence of treatment, bacteremia or sepsis may also occur and be fatal, particularly for the elderly, children and immuno-compromised if no antibiotic is administered in time [9].