Thirty-two strains of nonflocculating bacteria isolated from sewage-activated sludge were tested by a spectrophotometric assay for their ability to coaggregate with one other in two-membered systems. Among these strains, eight showed significant (74 to 99%) coaggregation with Acinetobacter johnsonii S35 while only four strains coaggregated, to a lesser extent (43 to 65%), with Acinetobacter junii S33. The extent and pattern of coaggregation as well as the aggregate size showed good correlation with cellular characteristics of the coaggregating partners. These strains were identified by sequencing of full-length 16S rRNA genes. A. johnsonii S35 could coaggregate with strains of several genera, such as Oligotropha carboxidovorans, Microbacterium esteraromaticum, and Xanthomonas spp. The role of Acinetobacter isolates as bridging organisms in multigeneric coaggregates is indicated. This investigation revealed the role of much-neglected nonflocculating bacteria in floc formation in activated sludge.The importance of bacterial aggregation as a primary step towards biofilm development, host colonization, and flocculation of activated sludge, etc., has long been realized. Efficient aggregation and proper settling of flocs is important for the generation of good-quality effluent in the activated sludge process. However, attention is focused mainly on floc-forming bacteria, such as Kluyvera cryocrescens, Pseudomonas sp., and Flavobacterium sp., etc. (7,8,21,22). The presence of nonflocculating bacteria is often considered a nuisance responsible for increased turbidity and poor quality of the treated effluent. As a result, it is difficult to contemplate the role of nonflocculating bacteria in floc formation.The ability of bacterial cells to recognize and communicate with one other, leading to coaggregation, is extensively investigated with regard to oral biofilms. A large amount of literature exists on the types and mechanisms of interactions in bacterial tooth plaques (5, 10), in addition to some reports on coaggregation of organisms in the urinogenital tract (16) and chicken crops (24). Relatively few studies of coaggregation between aquatic biofilm bacteria have been reported (3,17). Although environmental factors such as substrate gradient, chemical and/or physical stress, and predation are known to trigger bacterial aggregation in activated sludge systems (1), specific cell-cell interactions and coaggregation among pure cultures of nonflocculating sludge bacteria have never been investigated.This study explores and describes the possibility of intergeneric coaggregation among bacteria isolated from a municipal sewage treatment plant. A systematic study has been conducted to identify the coaggregating pairs among 32 strains of nonflocculating bacteria. The time courses and the aggregate sizes and structures have been examined in cases of efficient coaggregations. A correlation between coaggregation and the cellular characteristics of the partners has also been demonstrated. MATERIALS AND METHODSBacterial isolates. Fif...

Electrochromic materials (EMs) are widely used color-switchable materials, but their applications as stimuli-responsive biomaterials to monitor and control biological processes remain unexplored. This study reports the engineering of an organic π-electron structure-based EM (dicationic 1,1,4,4-tetra­aryl­buta­diene, 1 2+) as a unique hydrogen sulfide (H2S)-responsive chromophore amenable to build H2S-activatable fluorescent probes (1 2+-semiconducting polymer nanoparticles, 1 2+-SNPs) for in vivo H2S detection. We demonstrate that EM 1 2+, with a strong absorption (500–850 nm), efficiently quenches the fluorescence (580, 700, or 830 nm) of different fluorophores within 1 2+-SNPs, while the selective conversion into colorless diene 2 via H2S-mediated two-electron reduction significantly recovers fluorescence, allowing for non-invasive imaging of hepatic and tumor H2S in mice in real time. Strikingly, EM 1 2+ is further applied to design a near-infrared photosensitizer with tumor-targeting and H2S-activatable ability for effective photodynamic therapy (PDT) of H2S-related tumors in mice. This study demonstrates promise for applying EMs to build activatable probes for molecular imaging of H2S and selective PDT of tumors, which may lead to the development of new EMs capable of detecting and regulating essential biological processes in vivo.

Compounds with an ultralong CC single bond have been successfully constructed in three steps from commercially available dihalo aromatics. The intramolecular ''core-shell strategy'' is a key tactic for stabilizing compounds with an ultralong CC bond. Using this concept could lead to an even longer CC bond (''hyper covalent bonds'' with a bond length of 1.8-2.0 Å) because the covalently bonded state and non-bonded state are seamlessly connected in terms of the interatomic distance.

Afterglow luminescent probes with high signal-to-background ratio show promise for in vivo imaging; however, such probes that can be selectively delivered into target sites and switch on afterglow luminescence remain limited. We optimize an organic electrochromic material and integrate it into near-infrared (NIR) photosensitizer (silicon 2,3-naphthalocyanine bis(trihexylsilyloxide) and (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]) containing nanoparticles, developing an H 2 S-activatable NIR afterglow probe (F1 2+-ANP). F1 2+-ANP displays a fast reaction rate (1563 ± 141 M −1 s −1) and large afterglow turn-on ratio (~122-fold) toward H 2 S, enabling high-sensitivity and-specificity measurement of H 2 S concentration in bloods from healthy persons, hepatic or colorectal cancer patients. We further construct a hepatic-tumor-targeting and H 2 Sactivatable afterglow probe (F1 2+-ANP-Gal) for noninvasive, real-time imaging of tiny subcutaneous HepG2 tumors (<3 mm in diameter) and orthotopic liver tumors in mice. Strikingly, F1 2+-ANP-Gal accurately delineates tumor margins in excised hepatic cancer specimens, which may facilitate intraoperative guidance of hepatic cancer surgery.

The construction and switching properties of a novel class of molecular shuttles 1 with imine-bonding stations for macrocyclic diamine parts are reported. Studies on dithioacetalized [2]rotaxane 4 with two hydrogen-bonding stations and a masked imine-bonding station showed that protonation of a macrocycle increases the shuttling barrier due to hydrogen-bond formation between NH 3 (+) groups and the TEG-stations. Hydrolysis of the imine-bonds of the imine-bridged molecular shuttles 1b, c with TEG-stations could exclusively give the [2]rotaxane 2b, c.2H (2+), with the macrocycle hydrogen-bonded with the TEG-station. In contrast, 1a without TEG-stations gave an equilibrated mixture of 1a, monoimine 3a.H (+), and 2a.2H (2+) under similar acidic hydrolytic conditions. The equilibrium between 1b, c and 2b, c.2H (2+) to control the position of the macrocycle could be successfully switched to either side by applying acidic hydrolytic or dehydrating conditions. Furthermore, the equilibrium was largely biased to [2]rotaxane 2b, c.2H (2+) under acidic hydrolytic conditions and could be reversed in favor of bis-imine 1b, c just by heating. This is a successful example of a molecular shuttle exhibiting entropy-driven translational isomerism with remarkable positional discrimination. An examination of thermodynamic parameters showed that imine-bond hydrolyses and the formation of hydrogen bonds between the macrocycle and the station are thermodynamically matched processes, because both processes are enthalpically favored and accompanied by a loss of entropy. The combination of imine-bonding and hydrogen-bonding station in a rotaxane system is the key to realizing the clear entropy-driven positional switching of the macrocycle observed.