Microbially competent 3D skin: a test system that reveals insight into host-microbe interactions and their potential toxicological impact.

The skin`s microbiome is predominantly commensalic, harbouring a metabolic potential far exceeding that of its host. While there is clear evidence that bacteria-dependent metabolism of pollutants modulates the toxicity for the host there is still a lack of models for investigating causality of microbiome-associated pathophysiology or toxicity. We now report on a biologically characterised microbial-skin tissue co-culture that allows studying microbe-host interactions for extended periods of time in situ. The system is based on a commercially available 3D skin model. In a proof-of-concept, this model was colonised with single and mixed cultures of two selected skin commensals. Two different methods were used to quantify the bacteria on the surface of the skin models. While Micrococcus luteus established a stable microbial-skin tissue co-culture, Pseudomonas oleovorans maintained slow continuous growth over the 8-day cultivation period. A detailed skin transcriptome analysis showed bacterial colonisation leading to up to 3318 significant changes. Additionally, FACS, ELISA and Western blot analyses were carried out to analyse secretion of cytokines and growth factors. Changes found in colonised skin varied depending on the bacterial species used and comprised immunomodulatory functions, such as secretion of IL-1α/ß, Il-6, antimicrobial peptides and increased gene transcription of IL-10 and TLR2. The colonisation also influenced the secretion of growth factors such as VFGFA and FGF2. Notably, many of these changes have already previously been associated with the presence of skin commensals. Concomitantly, the model gained first insights on the microbiome's influence on skin xenobiotic metabolism (i.e., CYP1A1, CYP1B1 and CYP2D6) and olfactory receptor expression. The system provides urgently needed experimental access for assessing the toxicological impact of microbiome-associated xenobiotic metabolism in situ.

Structure and polymer form of poly-3-hydroxyalkanoates produced by Pseudomonas oleovorans grown with mixture of sodium octanoate/undecylenic acid and sodium octanoate/5-phenylvaleric acid.

PHAs (poly-3-hydroxyalkanoates) obtained by Pseudomonas oleovorans grown with mixed carbon sources were investigated. Mixed carbon sources were sodium octanoate/undecylenic acid and sodium octanoate/5-phenylvaleric acid. Effect of carbon source in pre-culture on PHAs structure was investigated. Main fermentation was conducted with mixture of sodium octanoate/undecylenic acid, and PHA contained both saturated and unsaturated units. When more undecylenic acid was used in the medium, the ratio of unsaturated unit increased and the T(g) of the products also changed. The PHA grown with mixture of sodium octanoate and undecylenic acid was a random copolymer, which was determined by DSC analysis. Using mixed carbon sources of sodium octanoate and 5-phenylvaleric acid, highest dry cell weight and PHA concentration were obtained when 0.02g or 0.04g of 5-phenylvaleric acid were added in 50mL medium. Cultured with sodium octanoate and 5-phenylvaleric acid, PHA containing HO (3-hydroxyoctanoate) unit and HPV (3-hydroxy-5-phenylvalerate) unit was produced. T(g) of the products fell between those of pure PHO and pure PHPV. By means of DSC analysis and fractionation method, the PHA obtained was regarded as a random copolymer.

Biosynthesis and characterization of deuterated polyhydroxyoctanoate.

The synthesis of a polyhydroxyalkanoate with medium chain length alkyl substituents by Pseudomonas oleovoranswas investigated using protonated and deuterated forms of octanoic acid in a minimal salts medium. Cultivation with deuterated octanoic acid resulted in a reduced rate of polymer accumulation compared to that with its protonated counterpart (107 and 207 mg of polymer L(-1) of medium h(-1) of cultivation, respectively). Nuclear magnetic resonance and gas chromatography coupled mass spectrometry of the derivatized polymer was used to establish the extent and distribution of deuterium in the biopolymer. A partially deuterated heteropolymer with 3-hydroxyoctanoic acid as the main constituent was produced. Deuteration is an important tool for contrast variation studies using neutron scattering, but predicates that the deuterated polymer is otherwise comparable in its physiochemical and material properties to its protonated counterpart. In studies reported here, the deuterated biopolymer exhibited an additional diffraction maximum at 7.55 A and slight differences in its melting point (60 and 55 degrees C) and glass transition temperature (-39 and -36 degrees C) when compared to its protonated equivalent. While significant differences between the protonated and deuterated biopolymers were determined, our results support the use of this deuterated polyhydroxyalkanoate in its application in investigations using analytical neutron scattering techniques.

Biosynthesis of natural-synthetic hybrid copolymers: polyhydroxyoctanoate-diethylene glycol.

A new natural-synthetic hybrid biomaterial has been isolated from the growth of Pseudomonas oleovorans in the presence of diethylene glycol (DEG). DEG was consumed by P. oleovorans with 20 mM sodium octanoate in modified E* medium, but its presence in the fermentation medium retarded cell growth and viability, influencing production and composition of polyhydroxyalkanoates with medium chain length substituents (mclPHAs) and consequently attenuating PHA yield. DEG affected the composition of the mclPHA with an increase in the C8 component: polyhydroxyoctanoate (PHO). Gas chromatography-mass spectrometry (GC-MS) was used to quantitatively monitor DEG in the system and reveal its cellular adsorption and penetration. Intracellularly, the DEG significantly reduced the molar mass of the mclPHA; PHO with a bimodal distribution of high and low molecular weight fractions was observed. 1H NMR, 2-D COSY, and heteronuclear single quantum coherence spectra confirmed that the high molecular weight fraction consisted of PHO chains terminated by DEG. Thus, the synthesis of this natural-synthetic hybrid copolymer, PHO-DEG, opens the way for microbial synthesis of a wide variety of PHA-DEG copolymers with a range of bioactive properties.

rpoS gene expression in carbon-starved cultures of the Polyhydroxyalkanoate-accumulating species Pseudomonas oleovorans.

The expression of the rpoS gene during PHA depolymerization was monitored in Pseudomonas oleovorans GPo1 and its mutant defective in PHA degradation by analyzing the tolerance to oxidative and thermal stresses and the RpoS intracellular content. An increase in the tolerance to H2O2 and heat shock was observed coincidentally with PHA degradation. Western blotting experiments performed in carbon-starved cultures showed that the RpoS levels were higher in the wild type than in the mutant strain. Complementation of the phaZ mutation restores the wild-type RpoS levels. These results suggest a probable association between PHA depolymerization and the stress tolerance phenotype controlled by RpoS.