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SummaryOrnithine lipids (OLs) are widespread among Gramnegative bacteria. Their basic structure consists of a 3-hydroxy fatty acyl group attached in amide linkage to the a-amino group of ornithine and a second fatty acyl group ester-linked to the 3-hydroxy position of the first fatty acid. OLs can be hydroxylated within the secondary fatty acyl moiety and this modification has been related to increased stress tolerance. Rhizobium tropici, a nodule-forming a-proteobacterium known for its stress tolerance, forms four different OLs. Studies of the function of these OLs have been hampered due to lack of knowledge about their biosynthesis. Here we describe that OL biosynthesis increases under acid stress and that OLs are enriched in the outer membrane. Using a functional expression screen, the OL hydroxylase OlsE was identified, which in combination with the OL hydroxylase OlsC is responsible for the synthesis of modified OLs in R. tropici. Unlike described OL hydroxylations, the OlsE-catalysed hydroxylation occurs within the ornithine moiety. Mutants deficient in OlsE or OlsC and double mutants deficient in OlsC/OlsE were characterized. R. tropici mutants deficient in OlsCmediated OL hydroxylation are more susceptible to acid and temperature stress. All three mutants lacking OL hydroxylases are affected during symbiosis.

In recent years, a strong interest has emerged in hybrid composites and their potential uses, especially in chitosan-titanium dioxide (CS-TiO 2 ) composites, which have interesting technological properties and applications. This review describes the reported advantages and limitations of the functionalization of chitosan by adding TiO 2 nanoparticles. Their effects on structural, textural, thermal, optical, mechanical, and vapor barrier properties and their biodegradability are also discussed. Evidence shows that the incorporation of TiO 2 onto the CS matrix improves all the above properties in a dose-dependent manner. Nonetheless, the CS-TiO 2 composite exhibits great potential applications including antimicrobial activity against bacteria and fungi; UV-barrier properties when it is used for packaging and textile purposes; environmental applications for removal of heavy metal ions and degradation of diverse water pollutants; biomedical applications as a wound-healing material, drug delivery system, or by the development of biosensors. Furthermore, no cytotoxic effects of CS-TiO 2 have been reported on different cell lines, which supports their use for food and biomedical applications. Moreover, CS-TiO 2 has also been used as an anti-corrosive material. However, the development of suitable protocols for CS-TiO 2 composite preparation is mandatory for industrial-scale implementation.Materials 2020, 13, 811 2 of 27 they are synthesized by different methods (intercalation of the polymer, sol-gel, hydrothermal, electro-deposition, chemical and physical vapor deposition, suspension and liquid phase deposition). These methods are effective to enhance the technological and mechanical properties of each individual component and also reveal new functionalities [1,3]. Currently, there is a special interest in combining natural polymers such as chitosan (CS) with inorganic materials like titanium dioxide (TiO 2 ) to obtain hybrid composites (CS-TiO 2 ) with beneficial properties [3][4][5][6].Chitosan (CS) is a natural biopolymer (linear polysaccharide comprising 1-4 linked 2-amino-deoxy-β-D-glucan) generally obtained by deacetylation of chitin, the main structural component of crustacean exoskeletons. CS exhibits a poly-cationic character and is non-toxic and biodegradable [7]. CS is considered a biological functional compound with multiple interesting properties. It can form films for food and pharmaceutical applications, including edible coatings, packaging material, or as drug-eluting carrier [5,7]. Its adsorbent capacity can have environmental applications during photocatalytic processes of waste-water treatment [8], and it also has inherent antibacterial and antifungal properties [9]. It is biocompatible with several organic and inorganic compounds by the presence of free amino and hydroxyl functional groups in its structure, which can react with other functional groups by electrostatic forces, hydrogen bonds, or by compound-soak up into the polymeric matrix, thus improving its mechanical and biological properties [10]...

Burkholderia cenocepacia is an important opportunistic pathogen, and one of the most striking features of the Burkholderia genus is the collection of polar lipids present in its membrane, including phosphatidylethanolamine (PE) and ornithine-containing lipids (OLs), as well as the 2-hydroxylated derivatives of PE and OLs (2-OH-PE and 2-OH-OLs, respectively), which differ from the standard versions by virtue of the presence of a hydroxyl group at C2 (2-OH) of an esterified fatty acyl residue. Similarly, a lipid A-esterified myristoyl group from Salmonella typhimurium can have a 2-hydroxy modification that is due to the LpxO enzyme. We thus postulated that 2-hydroxylation of 2-OH-OLs might be catalyzed by a novel dioxygenase homologue of LpxO. In B. cenocepacia, we have now identified two open reading frames (BCAM1214 and BCAM2401) homologous to LpxO from S. typhimurium. The introduction of bcam2401 (designated olsD) into Sinorhizobium meliloti leads to the formation of one new lipid and in B. cenocepacia of two new lipids. Surprisingly, the lipid modifications on OLs due to OlsD occur on the amide-linked fatty acyl chain. This is the first report of a hydroxyl modification of OLs on the amide-linked fatty acyl moiety. Formation of hydroxylated OLs occurs only when the biosynthesis pathway for nonmodified standard OLs is intact. The hydroxyl modification of OLs on the amide-linked fatty acyl moiety occurs only under acid stress conditions. An assay has been developed for the OlsD dioxygenase, and an initial characterization of the enzyme is presented.

TiO2-ZnO-MgO mixed oxide nanomaterials (MONs) were synthetized via the sol-gel method and characterized by scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), nitrogen physisorption analysis, X-ray diffraction (XRD), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), Fourier transform infrared spectroscopy (FTIR), and color (Luminosity (L), a, b, Chrome, hue) parameters. Furthermore, the antimicrobial activity of the MONs was tested against Escherichia coli (EC), Salmonella paratyphi (SP), Staphylococcus aureus (SA), and Listeria monocytogenes (LM). The MONs presented a semi globular-ovoid shape of ≤100 nm. Samples were classified as mesoporous materials and preserved in the TiO2 anatase phase, with slight changes in the color parameters of the MONs in comparison with pure TiO2. The MONs exhibited antimicrobial activity, and their effect on the tested bacteria was in the following order: EC > SP > SA > LM. Therefore, MONs could be used as antimicrobial agents for industrial applications.