Structure of the phytoplankton communities in two lagoons of different salinity in the Sfax saltern (Tunisia)

The structure and ecophysiological characteristics of phytoplanktonassemblages were studied for 10 months in two lagoons of differentsalinity (40 and 90) in the saltern of Sfax (Tunisia), in relationto environmental factors. These assemblages were largely dominatedby diatoms and dinoflagellates, which accounted for >90%of total abundance. A principal components analysis clearlydifferentiated the observations made in the two lagoons, thedominant correlate being the salinity. Euryhaline species andparticularly diatoms developed preferentially in the less salinelagoon, and were largely replaced by stenohaline species representedby dinoflagellates, which were dominant in the more saline lagoon.Calculation of the pigment diversity index and the species diversityindex showed that the phytoplankton assemblages studied werepermanently in a juvenile stage, as the species restructuringrelated to environmental constraints did not allow them to reachthe climax stage at any given time in their development. Despitethe heavy constraint imposed by the salinity, it is evidentthat other environmental factors, e.g. temperature, play a rolein the regulation of the planktonic communities. Finally, thedifference in the size distribution of the total microbial biomass,estimated by the assay of particulate proteins, showed thatthere was a significant change in the community structure andthe planktonic trophic networks, in parallel with the increasein salinity.     

Production of lysine by using immobilized livingCorynebacterium sp cells

Summary Lysine production by immobilizedCorynebacterium sp cells in alginate gel beads was investigated in flasks. ImmobilizedCorynebacterium sp cells exhibited a slightly greater lysine production than free cells and accumulated 60 g/l of L-lysine at maximum, when cultured for 120h in a medium containing 200g/l glucose as carbon source. Several factors, such as inoculum size, incubation time and alginate gel concentration were examined in order to improve lysine production by immobilized growing cells.     

Ethane production rates and minute ventilation

Ethane quantitated in the expired alveolar gas is a noninvasive measure of free radical activity. This method has been criticized for lack of control of minute ventilation (VE) in spontaneously breathing animals, although ethane, which is poorly soluble in tissues, should not be affected by changes in VE. We measured ethane elimination rates in six strain 13 guinea pigs (GP13) during spontaneous room air breathing and in six room air breathing, pentobarbital-anesthetized, tracheostomized, externally warmed, mechanically ventilated GP13s at various levels of VE. In the ventilated animals, weight0.75/VE (metabolic activity corrected for VE) was a linear function of arterial CO2 tension (PaCO2) drawn from arterial line (r = 0.72, P less than 0.005). However, weight0.75/VE did not correlate with ethane elimination rates (r = 0.12, not significant). The mean (+/- SD) ethane elimination rates in the spontaneously breathing animals was 3.15 +/- 0.96 pmol.min-1.100 g-1 and was not significantly different from the mean rate in the mechanically ventilated animals (3.11 +/- 1.37) over a range of VE's. These data demonstrate that ethane elimination rates are not affected by changes in VE and are unaffected by pentobarbital anesthesia.     

Syncytia formation in HIV-1 infected cells is associated with an increase in cellular oleic acid

Infection of cells with the human immunodeficiency virus type-1 (HIV-1) usually results in the formation of giant multinuclear cells (syncytia) [(1986) Nature 322, 470-474; (1986) Nature 322, 725-728; (1985) Hum. Pathol. 18, 760-765; (1987) Arm. Neurol. 21, 490-496]. The appearance of syncytia is associated with an increase in the monounsaturated oleic acid content. This report describes experiments which compare the activity of known antiviral agents with that of saturated fatty acid derivatives in inhibiting oleic acid and syncytia formation. A concept is introduced which proposes that infection of cells with the human immunodeficiency virus causes a rise in cellular oleic acid which leads to increased membrane fluidity.