Culture medium pH influence on Gluconacetobacter physiology: Cellulose production rate and yield enhancement in presence of multiple carbon sources.

Gluconacetobacter genera are valued for bacterial cellulose (BC) and acetic acid production. BC is produced at optimal yields in classical microbiological media that are expensive for a large scale of production. In addition, BC usage for industrial purposes is limited due to low conversion rate into cellulose and to long incubation duration. In this paper, Gluconacetobacter isolated from apple vinegar was kinetically studied to evaluate cellulose production in presence of different carbon sources. Acetic and citric acid effect on Gluconacetobacter metabolism is clarified. It was shown that Gluconacetobacter uses glucose as a primary carbon source for cells growth and products formation. Acetic acid employment as a co-carbon source in Hestrin Schramm medium showed an increase of 17% in BC yield with a moderate decrease in the crystallite size of the resulting polymer.

Role of Cu and pb on Ni bioaccumulation by Chlamydomonas reinhardtii: Validation of the biotic ligand model in binary metal Mixtures.

Ni, Pb and Cu uptake by Chlamydomonas reinhardtii has been quantified in single and binary metal systems in order to test some of the key assumptions of the biotic ligand model (BLM). Experiments were performed in solutions containing 5×10(-7)M of free metal at 30°C and pH 6. Nickel internalization fluxes (Jint) were measured in the presence of various concentrations of lead or copper from 5×10(-8)M to 5×10(-6)M at pH 6.0. Competition experiments did not show a straightforward antagonistic competition, as would be predicted by BLM. Synergistic and antagonistic effects were observed in binary metal systems which implies that bioaccumulation process is much more dynamic than assumed in the equilibrium models. Ni uptake decreased significantly in the presence of Cu(2+) concentrations higher than 5×10(-7)M. However, a maximum value of Ni uptake was observed at 5×10(-7)M Pb(2+). Cu(2+) was shown to compete strongly with Ni for uptake, having a higher binding affinity to Ni transport sites (KCu-Rs=10(6.95)M(-1)) than to Cu transport sites (KCu-Rs'=10(6.22)M(-1)). In contrast, the effect of Pb(2+) on Ni uptake could not be explained by a simple competitive equilibrium with the transport sites of Ni such as the BLM. On the other hand, internalization fluxes of Cu and Pb were nearly constant in the absence and in the presence of Ni, implying that nickel had no effect on the uptake of copper or lead. The calculated affinity constant of Cu to Ni transport sites in the presence of Ni was similar to that obtained in the absence of Ni (K'Cu-Rs'=10(6.22)M(-1)). It was further concluded that Cu and Pb did not interact with the same active sites on the cell surface. Ni and Cu were shown to interfere with Mg and Na transporters, while Pb uptake was thought to occur by the Ca pathway.

Bioaccumulation and biosorption of copper and lead by a unicellular algae Chlamydomonas reinhardtii in single and binary metal systems: a comparative study.

A comparative evaluation of bioaccumulation and biosorption of Cu (II) and Pb (II) ions by algal cells of Chlamydomonas reinhardtii was conducted in single and binary metal systems. Experiments were performed in solutions containing 5 × 10(-7) M of free metal at 30 °C and pH 6. Algal cells were used in the concentration of 0.2 g/L. Both processes tend to be more important as contact time between heavy metals and algal cells increases. Under studied conditions, dead cells showed higher removal efficiency than living cells for both metal ions. Removal efficiency of Pb increases from 8% to 40% when comparing the results obtained by living cells and dead cells. For Cu (II) ions, the removal efficiency of dead cells was about 2 times higher than living cells (55% vs. 28%). Living cells showed similar bioaccumulation capacity for both ions. Synergistic and antagonistic effects between copper and lead were observed in binary metal systems which imply that bioaccumulation process is much more dynamic than assumed in the equilibrium models. In contrast, dead algal cells showed a higher affinity for Pb (II) ions compared to Cu (II) ions and no competitive effect was observed in the biosorption of copper and lead by the inert cells in binary metal mixtures. Biosorption of Cu (II) and Pb (II) seems to occur at different binding sites on the surface of algal biomass. The obtained results showed that the mostly advantageous process of metal ions binding is biosorption and the biomass of C. reinhardtii is suitable for the development of an efficient and economic biosorbent for the removal of heavy metals from aqueous environments.