Tetracarboxylated Azobenzene/Polymer Supramolecular Assemblies as High-Performance Multiresponsive Actuators

Multistimuli-responsive polymers are materials of emerging interest but synthetically challenging. In this work, supramolecular assembly was employed as a facile and effective approach for constructing 3,3′,5,5′-azobenzene­tetracarboxylic acid (H₄abtc)/poly­(diallyl­dimethyl­ammonium chloride) (PDAC) supramolecules. Structural transformations of H₄abtc can be induced by light, mechanical force, and heat and influenced by free volume. Thus, the fabricated free-standing H₄abtc/PDAC film underwent bending/unbending movements upon treatment with light, humidity, or temperature, as asymmetric structural transformations on either side of the film generated asymmetric contraction/stretching forces. Fast rates of shape recovery were achieved for the film on exposure to gently flowing humid nitrogen. The bending/unbending motions are controllable, reversible, and repeatable. Hence, this light-, humido-, and thermo-responsive film has great potential in device applications for advanced functions

Solid-State Fluorescence of Fluorine-Modified Carbon Nanodots Aggregates Triggered by Poly(ethylene glycol)

Solid-state fluorescent carbon quantum dots (QDs) can be used for the encryption of security information. Controlling the dispersion and aggregation of the QDs is crucial for switching their solid-state fluorescence “on” and “off.” The use of polymers has been proposed to slightly separate the QDs inside aggregates to trigger their fluorescence. However, the complex interactions between the QDs and flexible polymer chains make this process challenging. Here, fluorine-modified carbon nanodots (FCDs) were used in a solution as the printing ink. After printing, the FCDs were aggregated on paper via hydrogen bonds, thereby quenching the fluorescence. After a poly­(ethylene glycol) (PEG) treatment, the FCDs exhibited yellow solid-state fluorescence due to an increased interdot spacing. The fluorescence intensity and emission wavelength could be tuned by varying the molecular weight and quantity of PEG used. Finally, we demonstrated a high-resolution encryption and decryption system based on the PEG-triggered fluorescence of FCDs

Epigenetic Switch Driven by DNA Inversions Dictates Phase Variation in <i>Streptococcus pneumoniae</i>

<div><p>DNA methylation is an important epigenetic mechanism for phenotypic diversification in all forms of life. We previously described remarkable cell-to-cell heterogeneity in epigenetic pattern within a clonal population of <i>Streptococcus pneumoniae</i>, a leading human pathogen. We here report that the epigenetic diversity is caused by extensive DNA inversions among <i>hsdS</i>_<i>A</i>, <i>hsdS</i>_<i>B</i>, and <i>hsdS</i>_<i>C</i>, three methyltransferase <i>hsdS</i> genes in the Spn556II type-I restriction modification (R-M) locus. Because <i>hsdS</i>_<i>A</i> encodes the sequence recognition subunit of this type-I R-M DNA methyltransferase, these site-specific recombinations generate pneumococcal cells with variable HsdS_A alleles and thereby diverse genome methylation patterns. Most importantly, the DNA methylation pattern specified by the HsdS_A1 allele leads to the formation of opaque colonies, whereas the pneumococci lacking HsdS_A1 produce transparent colonies. Furthermore, this HsdS_A1-dependent phase variation requires intact DNA methylase activity encoded by <i>hsdM</i> in the Spn556II (renamed <u>c</u>olony <u>o</u>pacity <u>d</u>eterminant or <i>cod</i>) locus. Thus, the DNA inversion-driven ON/OFF switch of the <i>hsdS</i>_<i>A1</i> allele in the <i>cod</i> locus and resulting epigenetic switch dictate the phase variation between the opaque and transparent phenotypes. Phase variation has been well documented for its importance in pneumococcal carriage and invasive infection, but its molecular basis remains unclear. Our work has discovered a novel epigenetic cause for this significant pathobiology phenomenon in <i>S</i>. <i>pneumoniae</i>. Lastly, our findings broadly represents a significant advancement in our understanding of bacterial R-M systems and their potential in shaping epigenetic and phenotypic diversity of the prokaryotic organisms because similar site-specific recombination systems widely exist in many archaeal and bacterial species.</p></div

Detection of DNA rearrangements in the Spn556II locus by PCR.

<p><b>A.</b> Positions of the primers used for PCR amplification in the Spn556II locus of ST556. The predicted rho-independent transcription terminator is indicated by a hairpin. The primers used in (<b>B</b>) and (<b>C</b>) are indicated by small arrows. The JC-replaced region in TH6501 is marked with dashed lines. <b>B.</b> Amplification of the Spn556II locus in ST556 and isogenic mutant TH5792 lacking the entire Spn556II locus with primers P1 and P11. The PCR mixtures were processed by DNA electrophoresis and stained by the Goldview dye (Yeasen, Beijing, China). The PCR products that were absent in the mutant strains are marked with asterisks (*). The sizes of the DNA markers are indicated in kilobases. <b>C.</b> Detection of DNA rearrangements in the <i>hsdS</i> regions of the Spn556II locus. PCR reactions were performed with the genomic DNA of ST556 using the same set of primer pairs indicated at the top of each lane, and marked as in (<b>B</b>). <b>D</b>. Same as in (C) except for using the genomic DNA from the ST556 derivative lacking <i>hsdS</i>_<i>A</i> strain (TH6501).</p

Significant impact of epigenetic-mediated phase variation on nasopharyngeal colonization of the pneumococci in the mouse co-carriage model.

<p>The pneumococcal derivatives of strains ST556 (A), P384 (B), and ST877 (C) each carrying the <i>hsdS</i>_<i>A1</i>, <i>hsdS</i>_<i>A2</i>, or <i>hsdS</i>_<i>A3</i> allele were grown on the TSA plates supplemented with catalase as represented in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005762#ppat.1005762.g006" target="_blank">Fig 6</a>. Two of the three unique <i>hsdS</i>_<i>A</i> allelic derivatives (A1, A2, and A3) from each strain background were mixed at a 1:1 ratio before being used to inoculate intranasally C57BL/6 mice. The colonizing pneumococci were recovered from each mouse by washing the nasal cavity 7 days post inoculation. The output ratio of the two the <i>hsdS</i>_<i>A</i> allele-specific variants co-infecting the same mouse was determined with the nasal lavage sample by PCR with the <i>hsdS</i>_<i>A</i> allele-specific primers. The <i>hsdS</i>_<i>A1</i>-specific variant derived from each of three different strain backgrounds (A1) (forming opaque colonies) was less fit than the counterpart carrying <i>hsdS</i>_<i>A2</i> (A2) or <i>hsdS</i>_<i>A3</i> (A3) (forming transparent colonies) in the nasopharynx.</p

Colony morphology of six <i>S</i>. <i>pneumoniae</i> strains and their derivatives each carrying an invariable <i>hsdS</i>_<i>A</i> allele.

<p>Pneumococcal strains ST556 (19F), P384 (6A), TH2901 (6B), TH2835 (14), TH2886 (23F), and ST877 (35B) were grown on TSA plates supplemented with catalase; the colonies photographed under a dissection microscope as described in reference [<a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005762#ppat.1005762.ref033" target="_blank">33</a>]. The Spn556II <i>hsdS</i>_<i>A</i> genotype and corresponding profile of chromosomal methylation in each strain are marked at the top of each column. Strain designation is indicated at the bottom of each photograph. The representative colonies with opaque and transparent appearance in the wild types are highlighted with blue and red arrowheads, respectively.</p

Significant impact of epigenetic-mediated phase variation on pneumococcal adhesion to host epithelial cells.

<p>The <i>hsdS</i>_<i>A1</i>, <i>hsdS</i>_<i>A2</i>, or <i>hsdS</i>_<i>A3</i> allele-carrying derivatives of strains ST556 (panels A and B), P384 (panels C and D), and ST877 (panels E and F) were cultured on the TSA plates supplemented with catalase as represented in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005762#ppat.1005762.g006" target="_blank">Fig 6</a>, and used to determine adhesion to human lung (A549 line) and nasopharyngeal (Detroit 562 line) cells in 24-well plates by counting CFU of adhering bacteria after extensive washing of the cell monolayers. The pneumococci carrying the <i>hsdS</i>_<i>A1</i> (A1) (producing opaque colonies) are significantly less adherent than those carrying the <i>hsdS</i>_<i>A2</i> (A2) or <i>hsdS</i>_<i>A3</i> (A3).</p

Essential roles of the DNA methyltransferase activity in defining pneumococcal colony opacity.

<p><b>A.</b> Necessity and sufficiency of <i>hsdM</i> and <i>hsdS</i>_<i>A</i> in defining pneumococcal colony opacity. Isogenic mutants each with an unmarked deletion in the coding region of <i>hsdR</i>, <i>hsdS</i>_<i>A</i>, <i>hsdRM or</i> Spn556II were constructed in the Spn556II locus of ST556. Colonies of each strain were prepared, photographed, and marked as in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005762#ppat.1005762.g006" target="_blank">Fig 6</a>. <b>B.</b> Requirement of the DNA methyltransferase catalytic activity in defining pneumococcal colony opacity. Strain TH6113 lacking the entire coding region of <i>hsdR</i> (MYY572) and <i>hsdM</i> (MYY571) (producing transparent colonies) was complemented with either the wild type <i>hsdM</i> gene (MYY571) or its catalytically inactive mutant with an E228A or N255A point mutation. Colonies are presented as in (<b>A</b>).</p

Requirement of <i>psrA</i> for the DNA inversion between the inverted repeats (IR1.1 and IR1.2).

<p>Amplification of the Spn556II <i>hsdS</i> region in ST556 (upper panel)(<b>A</b>), isogenic mutant lacking <i>psrA</i> (TH6012, middle panel)(<b>B</b>), or complemented TH6012 with the wild type <i>psrA</i> gene (TH6659, lower panel)(<b>C</b>) with primer pairs indicated at the top of each lane as in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005762#ppat.1005762.g002" target="_blank">Fig 2C</a>. The major band absent in TH6012 is marked with an asterisk (*).</p

Epigenetic-driven phase variation in unencapsulated pneumococci.

<p>The unencapsulated mutants of ST556 (parental strain TH8160) and D39 (parental strain TH7901) were used to generate single <i>hsdS</i>_<i>A</i> allele-locked strains by counter selection as described in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005762#ppat.1005762.g006" target="_blank">Fig 6</a>. Colonies of each strain were prepared and photographed as in <a href="http://www.plospathogens.org/article/info:doi/10.1371/journal.ppat.1005762#ppat.1005762.g006" target="_blank">Fig 6</a>. The strains in each row shared the same <i>hsdS</i>_<i>A</i> allele (A1, A2, or A3). The strains in each column were constructed from the same unencapsulated parental strain (top of each column). The name of each strain is listed at the bottom of each photograph.</p