Biomedical subjects
Publications and source records attributed to Pedro Fernandes.
An inexpensive and fast method based on images taken during growth of bacterial cells on multi-well plates was developed for biomass quantification. A correlation of 85% between the results obtained by image analysis and optical density measurements was obtained. This simple method allows the assessment of growth with highly aggregated cell cultures and the rapid screening of a large number of carbon sources.
This work aimed at studying the behavior and tolerance of Mycobacterium sp. NRRL B-3805, Rhodococcus erythropolis DCL14 and Pseudomonas putida S12 cells in the presence of various concentrations of water miscible (ethanol, butanol, and dimethylformamide, up to 50% v/v) and water immiscible solvents (dodecane, bis(2-ethylhexyl) phthalate and toluene, up to 5% v/v). When incubated in the presence of these solvents, the cells were found to have lower tolerance to butanol and toluene than to the remaining solvents. Nevertheless, the concentrations of solvents endured by the tested strains show that they are quite solvent-tolerant, confirming their potential as biocatalysts in nonconventional systems. Microscopic observation of samples showed that the hydrophobic Mycobacterium sp. and R. erythropolis cells were able to aggregate to protect the population under stress conditions. Comparison of the results obtained at the single cell level by fluorescence microscopy and colony development on agar plates indicated that the primary effects of most solvents tested were on the cell membrane and replicating capability of the cells.
This chapter summarizes the use of membrane reactors in extractive bioconversions as process integration systems leading to in situ product recovery. Several membrane reactor configurations are analyzed, taking into account the type of bioconversion, biocatalyst type and location (either in the aqueous phase or in the membrane), membrane chemistry and morphology, solvent (extractant) type and its biocompatibility. Modeling of liquid-liquid extractive membrane bioreactors operation is also analyzed considering kinetics and mass-transfer aspects. The chapter includes examples from the authors' laboratory as well as other published in the field. Both enzyme and whole cell-based bioconversions are considered. Relevant aspects related to the solvent (extractant) toxicity and how the membrane could protect the biocatalytic activity are analyzed. Trends in this field are also given.
Microorganisms have mechanisms that enable them to tolerate lethal concentrations of toxic compounds. This feature has been exploited in a wide range of bioprocesses that range from bioremediation applications to production of fine chemicals in two-phase reaction media. The ability to modify the physical properties of cellular membranes has long been put forward as a protection mechanism that enables microorganisms to tolerate solvents. More recently, efflux pumps have been shown to extrude deleterious compounds, such as antibiotics, drugs and solvents. An understanding of the mechanism of solvent tolerance and its relationship to cross-resistance of pathogenic organisms to antibiotics has major impact on the type and use of disinfectants and disinfecting procedures. The presence of solvents in the growth environment may lead to the emergence of solvent resistant strains and, therefore, overuse may propagate resistant microbial variants. In this paper, mechanisms that lead to solvent tolerance of microbes and accompanying specific antibiotic resistance are reviewed.