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The two-component system (TCS) is a conserved signal transduction module in bacteria. The Hik2-Rre1 system is responsible for transcriptional activation upon high-temperature shift as well as plastoquinone-related redox stress in the cyanobacterium Synechococcus elongatus PCC 7942. As heat-induced de novo protein synthesis was previously shown to be required to quench the heat-activated response, we investigated the underlying mechanism in this study. We found that the heat-inducible transcription activation was alleviated by the overexpression of dnaK2 , which is an essential homolog of the highly conserved HSP70 chaperone and whose expression is induced under the control of the Hik2-Rre1 TCS. Phosphorylation of Rre1 correlated with transcription of the regulatory target hspA. The redox stress response was found to be similarly repressed by dnaK2 overexpression. Considered together with the previous information, we propose a negative feedback mechanism of the Hik2-Rre1-dependent stress response that maintains the cellular homeostasis mediated by DnaK2. [ABSTRACT FROM AUTHOR]

The formation of photosynthetic microbial biofilms comprising multispecies biomolecules, such as extracellular polymeric substances (EPSs), and microbial cells play pivotal roles in maintaining or stimulating their biological functions. Although there are numerous studies on photosynthetic microbial biofilms, the spatial distribution of EPS components that are vital for microbial biofilm formation, such as exopolysaccharides and proteins, is not well understood. Visualization of photosynthetic microbial biofilms requires label-free methods, because labelling EPSs results in structural changes or aggregation. Raman spectroscopy is useful for label-free visualization of biofilm constituents based on chemical contrast. However, interference resulting from the bright autofluorescence of photosynthetic molecules and the low detection efficiency of Raman scattering make visualization a challenge. Herein, we visualized photosynthetic microbial biofilms in a label-free manner using a super-resolution optical infrared absorption imaging technique, called mid-infrared photothermal (MIP) microscopy. By leveraging the advantages of MIP microscopy, such as its sub-micrometer spatial resolution, autofluorescence-free features, and high detection sensitivity, the distribution of cyanobacteria and their extracellular polysaccharides in the biofilm matrix were successfully visualized. This showed that cyanobacterial cells were aligned along acidic/sulfated polysaccharides in the extracellular environment. Furthermore, spectroscopic analyses elucidated that during formation of biofilms, sulfated polysaccharides initially form linear structures followed by entrapment of cyanobacterial cells. The present study provides the foundation for further studies on the formation, structure, and biological functions of microbial biofilms. [ABSTRACT FROM AUTHOR]

Cyanobacteria are promising photosynthetic organisms owing to their ease of genetic manipulation. Among them, Synechococcus elongatus UTEX 2973 exhibits faster growth, higher biomass production efficiency and more robust stress tolerance compared with S. elongatus PCC 7942. This is due to specific genetic differences, including four single-nucleotide polymorphisms (SNPs) in three genes. One of these SNPs alters an amino acid at position 252 of the FoF1 ATP synthase α-subunit from Tyr to Cys (αY252C) in S. elongatus 7942. This change has been shown to significantly affect growth rate and stress tolerance, specifically in S. elongatus. Furthermore, experimental substitutions with several other amino acids have been shown to alter the ATP synthesis rate in the cell. In the present study, we introduced identical amino acid substitutions into Synechocystis sp. PCC 6803 at position 252 to elucidate the amino acid's significance and generality across cyanobacteria. We investigated the resulting impact on growth, intracellular enzyme complex levels, intracellular ATP levels and enzyme activity. The results showed that the αY252C substitution decreased growth rate and high-light tolerance. This indicates that a specific bulkiness of this amino acid's side chain is important for maintaining cell growth. Additionally, a remarkable decrease in the membrane-bound enzyme complex level was observed. However, the αY252C substitution did not affect enzyme activity or intracellular ATP levels. Although the mechanism of growth suppression remains unknown, the amino acid at position 252 is expected to play an important role in enzyme complex formation. [ABSTRACT FROM AUTHOR]

[TiCl.sub.4]-mediated Friedel-Crafts benzylation of benzene with 8-(bromomethyl)[2.2]metacyclophanes to afford 8-benzyl[2.2] metacyclophanes is described. Substituent effect through space on the rate of the benzylation of benzene with a bromomethyl group attached on the opposite aromatic ring was first found in this investigation. Interestingly, the introduction of the substituents at the internal position 16 tends to promote the present benzylation reaction rate 1.8-3.8 times. It was found that the benzyl cation intermediate was stabilized by the the direct through-space cation-πt interaction among the opposite benzene ring in the benzylation of [2.2]metacyclophane systems. Key words: cyclophanes, Friedel-Crafts benzylation, benzyl cation intermediate, through-space electronic interaction. On decrit la reaction de benzylation du benzene par le 8-bromomethyl)[2,2]metacyclophanes par la meethode de Friedel-Crafts catalysee par le [TiCl.sub.4]. Dans ce travail, on a mis en evidence pour la premiere fois, un effet de substituant qui se fait sentir a travers l'espace sur la vitesse de benzylation du benzene en raison d'un groupe bromomethyle attacheee sur le noyau aromatique oppose. Il est interessant de noter que l'introduction de substituants a la position interne 16 tendent a acceterer les vitesses de reaction de benzylation par des facteurs allant de 1,8 a 3,8. On a trouvee que le cation benzylique intermeediaire est stabilise; par une interaction cation-π directe a travers l'espace du noyau benzeenique oppose dans la benzylation de systemes [2,2] meetacyclophanes. Mots-cles: cyclophanes, benzylation suivant Friedel-Crafts, cation benzylique intermeediaire, interaction electronique a travers l'espace., Introduction The geometry of the [2.2]metacyclophane ([2.2]MCP) skeleton is known in detail from an X-ray structural analysis. (2,3) The crystal consists of discrete molecules, each of which has a center [...]