Immobilization of E. coli bacteria in three-dimensional matrices for ISFET biosensor design.

In recent years, cell-based biosensors (CBBs) have been very useful in biomedicine, food industry, environmental monitoring and pharmaceutical screening. They constitute an economical substitute for enzymatic biosensors, but cell immobilization remains a limitation in this technology. To investigate into the potential applications of cell-based biosensors, we describe an electrochemical system based on a microbial biosensor using an Escherichia coli K-12 derivative as a primary transducer to detect biologically active agents. pH variations were recorded by an ion-sensitive field effect transistor (ISFET) sensor on bacteria immobilized in agarose gels. The ISFET device was directly introduced in 100 ml of this mixture or in a miniaturized system using a dialysis membrane that contains 1 ml of the same mixture. The bacterial activity could be detected for several days. The extracellular acidification rate (ECAR) was analyzed with or without the addition of a culture medium or an antibiotic solution. At first, the microorganisms acidified their micro-environment and then they alkalinized it. These two phases were attributed to an apparent substrate preference of bacteria. Cell treatment with an inhibitor or an activator of their metabolism was then monitored and streptomycin effect was tested.

The anaerobic treatment of sewage and granule formation in upflow anaerobic sludge blanket reactor.

The granulation process was examined using synthetic wastewater containing glucose in a 1 liter laboratory upflow anaerobic sludge blanket (UASB) reactor. The anaerobic biotransformation of glucose was investigated during the granulation process. Anaerobic unacclimated sludge and glucose were used as seed and primary substrate, respectively. Massive initial granules were developed after three months of start-up. The effect of operational parameters such as influent glucose concentrations, pH, Volatile Fatty Acids (VFA) were also considered during granulation. The presence of a large concentration of sulphate in the sludge of a mesophilic (37 degrees C+/-1 degrees C) UASB reactor treating sewage resulted in severe process disturbance, with a complete inhibition of the propionate-degrading ability of the sludge. Severe inhibition of acetate removal was also observed, with concentrations of propionic acid and acetic acid in the reactor effluent of 1.72% and 18.88%, respectively. Hydrogen sulfide (H2S) is formed from the anaerobic decomposition of organic matter containing sulfate by sulfate-reducing bacteria. This gas is toxic at rate exceeding 2% tolerable by a reactor. The result shows the rate of hydrogen sulfide production was 3.8 %.