Daily battle against body odor: towards the activity of the axillary microbiota.

The microbial community of the human axilla plays a key role in the formation of axillary odor by biotransformation of odorless natural secretions into volatile odorous molecules. Culture-based microbiological and biochemical studies have allowed the characterization of the axillary microbiota, but the advent of next-generation culture-independent DNA sequencing approaches has provided an unprecedented depth of data regarding the taxonomic composition of the axillary microbiota and intra- and interindividual variation. However, the physiological activity of the microbiota of an individual and its variation under different environmental conditions remains largely unknown. Thus, metatranscriptomics represents a promising technique to identify specific metabolic activities in the axillary microbiota linked to individual differences in body odor.

The transcriptional regulatory network of Corynebacterium jeikeium K411 and its interaction with metabolic routes contributing to human body odor formation.

Lipophilic corynebacteria are involved in the generation of volatile odorous products in the process of human body odor formation by degrading skin lipids and specific odor precursors. Therefore, these bacteria represent appropriate model systems for the cosmetic industry to examine axillary malodor formation on the molecular level. To understand the transcriptional control of metabolic pathways involved in this process, the transcriptional regulatory network of the lipophilic axilla isolate Corynebacterium jeikeium K411 was reconstructed from the complete genome sequence. This bioinformatic approach detected a gene-regulatory repertoire of 83 candidate proteins, including 56 DNA-binding transcriptional regulators, nine two-component systems, nine sigma factors, and nine regulators with diverse physiological functions. Furthermore, a cross-genome comparison among selected corynebacterial species of the taxonomic cluster 3 revealed a common gene-regulatory repertoire of 44 transcriptional regulators, including the MarR-like regulator Jk0257, which is exclusively encoded in the genomes of this taxonomical subline. The current network reconstruction comprises 48 transcriptional regulators and 674 gene-regulatory interactions that were assigned to five interconnected functional modules. Most genes involved in lipid degradation are under the combined control of the global cAMP-sensing transcriptional regulator GlxR and the LuxR-family regulator RamA, probably reflecting the essential role of lipid degradation in C. jeikeium. This study provides the first genome-scale in silico analysis of the transcriptional regulation of metabolism in a lipophilic bacterium involved in the formation of human body odor.

Continuous and reversible mixing or demixing of nanoparticles by dielectrophoresis.

Mixing and demixing (separation) are essential tasks in microfluidic devices, which seem to be contrary in nature. Accordingly, completely different strategies and devices are usually employed for their realization. We here present a microfluidic device which is capable of performing both these tasks as it can be operated in either mixing or demixing mode. The mixing and demixing processes are reversible and are accomplished by continuous operation of the device. An asymmetric S-shaped ridge extends over the full width of a microfluidic channel (200 µm) creating a constriction of 620 nm in height with an aspect ratio of 1 : 500. Appropriate AC and DC voltages generate electrodeless dielectrophoresis at the constriction as well as (linear) electrokinetic driving forces along the channel. These de/mixing parameters can be adapted in real time in such a way that continuous separation and mixing efficiencies of 85-100% can be achieved. As a proof of concept we demonstrate continuous mixing and demixing of polystyrene nanoparticles (20 and 100 nm). The experimental results are complemented by numerical simulations illustrating the particles' motion under the influence of the electrokinetic effects and thermal noise (diffusion). The monolithic one-step fabrication process by soft lithography (with PDMS in our case) will make integration and combination of several mixing and demixing functions into a more complex lab-on-a-chip device possible.