Control over structural transformations in supramolecular entities by external stimuli is critical for the development of adaptable and functional soft materials. Herein, we have designed and synthesized a dipyridyl donor containing a central Z-configured stiff-stilbene unit that self-assembles in the presence of two 180°di-Pt(II) acceptors to produce size-controllable discrete organoplatinum(II) metallacycles with high efficiency by means of the directionalbonding approach. These discrete metallacycles undergo transformation into extended metallosupramolecular polymers upon the conformational switching of the dipyridyl ligand from Z-configured (0°) to E-configured (180°) when photoirradiated. This transformation is accompanied by interesting morphological changes at nanoscopic length scales. The discrete metallacycles aggregate to spherical nanoparticles that evolve into long nanofibers upon polymer formation. These fibers can be reversibly converted to cyclic oligomers by changing the wavelength of irradiation, which reintroduces Z-configured building blocks owing to the reversible nature of stiff-stilbene photoisomerization. The design strategy defined here represents a novel self-assembly pathway to deliver advanced supramolecular assemblies by means of photocontrol.metal coordination | supramolecular coordination complex | photoirradiation | reversibility | dynamic materials N atural systems provide many examples of self-assembled biosupramolecules that respond to external stimuli through conformational changes that ultimately play a role in carrying out their various biological functions. Mimicking this stimuli-responsive behavior in artificial systems is a promising route toward obtaining sophisticated molecular-based architectures with functional and structural tunability (1-3). Using the absorption of photons as a trigger is particularly attractive in that light-induced transformations maintain high spatial and temporal resolution without producing waste products even during multiple reversible switching sequences (4). In materials science, one of the most appealing characteristics of photochromic molecules is the direct conversion of light into mechanical energy based on their photo-reversible structural transformations (5). Among such chromophores, a stiffstilbene moiety (1,1′-biindane) is useful owing to its unique characteristics (6). First, stiff stilbene can adopt either a cis or trans configuration with respect to its central double bond. Second, the high activation barrier between the two isomers (∼43 kcal·mol −1 , corresponding to a half-life of ∼10 9 y at 300 K) makes thermal E/Z isomerization negligible at temperatures of 420 K and lower. Third, the quantum yield for the photoisomerization of either isomer is high (50%). Fourth, the stiff-stilbene core is readily substituted using well-established synthetic methods. Owing to these promising characteristics, Boulatov and coworkers (7) constructed a molecular force probe by integrating the moiety into a stretched polymer to mimic the strain gen...

Streptococcus thermophilus is the most important thermophilic dairy starter, and is widely used in the dairy industry. Streptococcus thermophilus exopolysaccharides received wide attention over recent decades, because they can improve the properties of the dairy product and confer beneficial health effects. The understanding of the regulatory and biosynthetic mechanisms of EPS will improve the EPS biosynthesis, increase the productivity of EPSs, and develop EPSs with desirable properties. The structure of EPSs is the focus of this study. Revealing the structure-function relationship can lead to increase the knowledge base and from there to increased research of EPS. The EPS yield is a key limiting factor in the research and utilization of EPS. In the present review, biosynthetic pathways and genetics of S. thermophilus EPSs were described and reviewed. At the same time, functional properties and applications of EPS, and strategies for enhancement of EPS production are discussed.

Streptococcus thermophilus is one of the most valuable homo-fermentative lactic acid bacteria, which, for a long time, has been widely used as a starter for the production of fermented dairy products. The key production characteristics of S. thermophilus, for example the production of extracellular polysaccharide, proteolytic enzymes and flavor substances as well as acidifying capacity etc., have an important effect on the quality of dairy products. The acidification capacity of the strains determines the manufacturing time and quality of dairy products. It depends on the sugar utilization ability of strains. The production of extracellular polysaccharide is beneficial for improving the texture of dairy products. Flavor substances increase the acceptability of dairy products. The proteolytic activity of the strain influences not only the absorption of the nitrogen source, but also the formation of flavor substances. Different strains have obvious differences in production characteristics via long-time evolution and adaptation to environment. Gaining new strains with novel and desirable characteristics is an important long-term goal for researchers and the fermenting industry. The understanding of the potential molecular mechanisms behind important characteristics of different strains will promote the screening and breeding of excellent strains. In this paper, key technological and functional properties of different S. thermophilus strains are discussed, including sugar metabolism, proteolytic system and amino acid metabolism, and polysaccharide and flavor substance biosynthesis. At the same time, diversity of genomes and plasmids of S. thermophilus are presented. Advances in research on key production characteristics and molecular levels of S. thermophilus will increase understanding of molecular mechanisms of different strains with different important characteristics, and improve the industrialization control level for fermented foods.

Butenoic acid is a C4 short-chain unsaturated fatty acid mainly used in the preparation of resins, pharmaceuticals, and fine chemicals. However, butenoic acid derived from petroleum is costly and unfriendly to the environment. Here, we report a novel biosynthetic strategy to produce butenoic acid by utilizing the intermediate of fatty acid biosynthesis pathway in engineered Escherichia coli. A thioesterase gene (B. thetaiotaomicron thioesterase (bTE)) from Bacteroides thetaiotaomicron was heterologously expressed in E. coli to specifically convert butenoyl-acyl carrier protein (ACP), a fatty acid biosynthesis intermediate, to butenoic acid. The titer of butenoic acid ranged from 0.07 to 11.4 mg/L in four different E. coli strains with varied expressing vectors. Deletion of endogenous fadD gene (encoding acyl-CoA synthetase) to block fatty acid oxidation improved the butenoic acid production in all strains to some extent. The highest butenoic acid accumulation of 18.7 mg/L was obtained in strain XP-2 (BL21-∆fadD/pET28a-bTE). Moreover, partially inhibiting the enoyl-ACP reductase (FabI) of strain XP-2 by triclosan increased butenoic acid production by threefold, and the butenoic acid titer was further increased to 161.4 mg/L by supplying glucose and tryptone in the M9 medium. Fed-batch fermentation of this strain further enhanced butenoic acid production to 4.0 g/L within 48 h. The butenoic acid tolerance assay revealed that this strain could tolerate 15-20 g/L of butenoic acid.