Luffa cylindrica and phytosterols bioconversion: from shake flask to jar bioreactor.

Bioconversion of lipophilic compounds poorly soluble in water, such as sterols, required the use of chemicals and solubilizing agents. On the other hand, it was shown that immobilization of Mycobacterium species on the dried fruit of Luffa cylindrica (DFLC) allows a close interaction between immobilized cells and cholesterol particles and increases by then the product's yield. In this work, the use of DFLC in a 5-l jar bioreactor with phytosterols mixture (1 g/l) as substrate was assessed without addition of any chemicals or solubilizing agents. DFLC increased by a factor of four the volumetric productivity of androstenones (0.08 g/l day). Products were accumulated in the aqueous medium while substrates remained on the fibers of DFLC. This observation lets envisage a green semi-continuous process of androstenone production. DFLC has no influence on cell growth, and is moreover natural, inexpensive, non-toxic, and mechanically strong.

Performance of Luffa cylindrica as immobilization matrix in bioconversion reactions by Nicotiana tabacum BY-2.

The dry fruit of Luffa cylindrica was investigated as an immobilization matrix for Nicotiana tabacum cells in bioconversion reactions of exogenous substrates. Immobilized cells show high biocatalytic activity under high substrate levels. Cell growth on the dry fruit can be maintained until reaching an immobilization capacity of 1.8 g cells/g(Luffa).

Quantitative and morphological analysis of biofilm formation on self-assembled monolayers.

In spite of intensive studies over the past two decades, the influence of surface properties on bacterial adhesion and biofilm formation remains unclear, particularly on late steps. In order to contribute to the elucidation of this point, we compared the impact of two different substrates on the formation of bacterial biofilm, by analysing bacterial amount and biofilm structure on hydrophilic and hydrophobic surfaces. The surfaces were constituted by NH(2)- and CH(3)-terminated self-assembled monolayers (SAMs) on silicon wafers, allowing to consider only the surface chemistry influence because wafers low roughness. A strain of Escherichia coli K12, able to produce biofilm on abiotic surfaces, was grown with culture durations varying from 4h to 336 h on both types of substrates. The amount of adhered bacteria was determined after detachment by both photometry at 630 nm and direct counting under light microscope, while the spatial distribution of adhered bacteria was observed by fluorescence microscopy. A general view of our results suggests a little influence of the surface chemistry on adherent bacteria amount, but a clear impact on dynamics of biofilm growth as well as on biofilm structure. This work points out how surface chemistry of substrates can influence the bacterial adhesion and the biofilm formation.

Influence of growth conditions on Pseudomonas fluorescens strains: a link between metabolite production and the PLFA profile.

Phospholipid fatty acids (PLFA) are essential constituents of cell membranes. PLFA fingerprints can be used to monitor the impact of growth conditions on bacteria because the fatty acid composition is closely linked to the growth environment. Through statistical analyses, clusters can be shown connecting the PLFA of Pseudomonas fluorescens with the growth condition. The metabolite production/excretion by bacteria is shown to be related to such clusters. This suggests that modification of the cell membrane, due to the variations in the fatty acid composition, is linked to the presence of metabolites in the bacterial culture media.

Detection of 1,2-hydride shifts in the formation of euph-7-ene by the squalene-tetrahymanol cyclase of Tetrahymena pyriformis.

Incubation of samples of 2,3-dihydrosqualene, specifically labeled with deuterium at either carbon position 7 or 11, with an enzyme extract from Tetrahymena pyriformis, containing a squalene-tetrahymanol cyclase, provided specimens of euph-7-enes displaying deuterium patterns consistent with the biosynthetic operation of two consecutive 1,2-hydride shifts.

Influence of the temperature and the growth phase on the hopanoids and fatty acids content of Frateuria aurantia (DSMZ 6220).

The main lipids isolated from Frateuria aurantia (DSMZ 6220) are iso-branched fatty acids and triterpenoids of the hopane family like bacteriohopanetetrol and derived hopanoids, beside trace amounts of diploptene and rearranged compounds like fern-7-ene. The impact of the growth temperature and the growth phase in which cells were harvested on this lipid fingerprint was investigated. As expected, an increase of saturated compounds with temperature is the essential modification in the fatty acid composition. The fatty acid composition also varies significantly during the growth. Global lipid fingerprints, including at least PLFA and triterpenoids are suggested to be a tool for measuring the stress state of bacterial cells. Increasing amounts of C-31 hydroxylated hopanoids with a temperature increase is novel information which deserves attention and further investigation for a better comprehension of the physiological significance of modifications conditioned obviously by environmental changes.