Toluene permeabilization differentially affects F- and P-type ATPase activities present in the plasma membrane of Streptococcus mutans

Synthesis of natural variants and synthetic derivatives of the cyclic nonribosomal peptide luminmide in permeabilized E. coli Nissle and product formation kinetics

We used a recombinant, permeabilized E. coli Nissle strain harbouring the plu3263 gene cluster from Photorhabdus luminescens for the synthesis of luminmide type cyclic pentapeptides belonging to the class of nonribosomally biosynthesized peptides (NRP). Cells could be fully permeabilized using 1 % v/v toluene. Synthesis of luminmides was increased fivefold when 0.3 mM EDTA was added to the substrate mixture acting as an inhibitor of metal proteases. Luminmide formation was studied applying different amino acid concentrations. Apparent kinetic parameters for the synthesis of the main product luminmide A from leucine, phenylalanine and valine were calculated from the collected data. K _s^app values ranged from 0.17 mM for leucine to 0.57 mM for phenylalanine, and r _max^app was about 3 × 10^-8 mmol min^-1(g CDW)^-1). By removing phenylalanine from the substrate mixture, the formation of luminmide A was reduced tenfold while luminmide B was increased from 50 to 500 μg/l becoming the main product. Two new luminmides were synthesized in this study. Luminmide H incorporates tryptophan replacing phenylalanine in luminmide A. In luminmide I, leucine was replaced with 4,5-dehydro-leucine, a non-proteinogenic amino acid fed to the incubation mixture. Our study shows new opportunities for increasing the spectrum of luminmide variants produced, for improving production selectivity and for kinetic in vitro studies of the megasynthetases.

Directed multistep biocatalysis using tailored permeabilized cells

: Recent developments in the field of biocatalysis using permeabilized cells are reviewed here, with a special emphasis on the newly emerging area of multistep biocatalysis using permeabilized cells. New methods of metabolic engineering using in silico network design and new methods of genetic engineering provide the opportunity to design more complex biocatalysts for the synthesis of complex biomolecules. Methods for the permeabilization of cells are thoroughly reviewed. We provide an extended review of useful available databases and bioinformatics tools, particularly for setting up genome-scale reconstructed networks. Examples described include phosphorylated carbohydrates, sugar nucleotides, and polyketides.

Development of a whole-cell biocatalyst co-expressing P450 monooxygenase and glucose dehydrogenase for synthesis of epoxyhexane

Oxygenases-based Escherichia coli whole-cell biocatalyst can be applied for catalysis of various commercially interesting reactions that are difficult to achieve with traditional chemical catalysts. However, substrates and products of interest are often toxic to E. coli, causing a disruption of cell membrane. Therefore, organic solvent-tolerant bacteria became an important tool for heterologous expression of such oxygenases. In this study, the organic solvent-tolerant Bacillus subtilis 3C5N was developed as a whole-cell biocatalyst for epoxidation of a toxic terminal alkene, 1-hexene. Comparing to other hosts tested, high level of tolerance towards 1-hexene and a moderately hydrophobic cell surface of B. subtilis 3C5N were suggested to contribute to its higher 1,2-epoxyhexane production. A systematic optimization of reaction conditions such as biocatalyst and substrate concentration resulted in a 3.3-fold increase in the specific rate. Co-expression of glucose dehydrogenase could partly restored NADPH-regenerating ability of the biocatalyst (up to 38 % of the wild type), resulting in approximately 53 % increase in specific rate representing approximately 22-fold increase in product concentration comparing to that obtained prior to an optimization.

Genotypic and phenotypic analysis of S. mutans isolated from dental biofilms formed in vivo under high cariogenic conditions

The oral cavity harbors several Streptococcus mutans genotypes, which could present distinct virulence properties. However, little is known about the diversity and virulence traits of S. mutans genotypes isolated in vivo under controlled conditions of high cariogenic challenge. This study evaluated the genotypic diversity of S. mutans isolated from dental biofilms formed in vivo under sucrose exposure, as well as their acidogenicity and aciduricity. To form biofilms, subjects rinsed their mouths with distilled water or sucrose solution 8 times/day for 3 days. S. mutans collected from saliva and biofilms were genotyped by arbitrarily-primed PCR. Genotypes identified in the biofilms were evaluated regarding their ability to lower the suspension pH through glycolysis and their acid susceptibility and F-ATPase activity. Most subjects harbored only one genotype in saliva, which was detected in almost all biofilm samples at high proportions. Genotypes isolated only in the presence of sucrose had higher acidogenicity than those isolated only in the presence of water. Genotypes from biofilms formed with sucrose were more aciduric after 30 and 60 min of incubation at pH 2.8 and 5.0, respectively. The present results suggest that biofilms formed under high cariogenic conditions may harbor more aciduric and acidogenic S. mutans genotypes.