Feeding in the megalopae of the mud crab (<i>Scylla paramamosain</i>): mechanisms, plasticity, role of chelipeds and effect of prey density

<div><p>We used microscopic video records to analyse the behaviour of mud crab megalopae (<i>Scylla paramamosain</i>) fed on rotifers (<i>Brachiomus</i> spp.), <i>Artemia</i> sp. or copepods (<i>Schmackeria dubin</i>). The megalopae were able to capture prey whose sizes ranged from no larger than <i>Artemia</i> nauplii to no smaller than adult <i>Artemia</i>. The megalopae employed three feeding modes: (1) Ambush-Prey mode, (2) Swim-Suspension-Feed mode and (3) Sit-Sweep mode. These involved raptorial feeding, suspension feeding and an in-between raptorial-suspension feeding mode, depending on the size of the prey and their density in the surrounding water. The chelipeds played an important role in feeding. Megalopae used the chelipeds to grip or sweep prey items and their movement generated eddies that can increase feeding efficiency. To verify the contribution of the chelipeds to feeding efficiency, we observed and compared the animals under three cheliped treatment regimes: (1) Autotomized – chelipeds removed by induced autotomy; (2) Glued – chelipeds glued at the dactylus-propodus joint to eliminate their ability to grip; and (3) Control – normal chelipeds. The feeding rates of the autotomized and glued treatments were lower than those of the controls, demonstrating that the chelipeds assist in feeding but that the megalopae can still feed without them. The density of prey also affected feeding efficiency. Feeding rate and prey density were positively correlated. When prey density was high, megalopae were able to feed in excess of their nutritional requirements. The study shows that mud crab megalopae respond flexibly to variations in feeding conditions, such as damaged chelipeds, as well as prey size and density. We postulate that this plasticity evolved in response to the dilute and patchy prey conditions of the estuarine environment. All the analysed behaviours are illustrated with video sequences.</p></div

A Water-Soluble Galactose-Decorated Cationic Photodynamic Therapy Agent Based on BODIPY to Selectively Eliminate Biofilm

A multitude of serious chronic infections are involved in bacterial biofilms that are difficult to eradicate. Here, a water-soluble galactose-functionalized cationic 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY)-based photodynamic therapy agent was synthesized for selectively eliminating the bacterial biofilm. These conjugates can capture bacteria to form aggregations through electrostatic interaction and then generate a large number of reactive oxygen species (ROS) under visible light irradiation to kill the bacteria without the emergence of bacterial resistance. Simultaneously, this agent could effectively inhibit and eradicate both Gram-positive and Gram-negative bacterial biofilms. The in-depth analysis of the antimicrobial mechanism confirmed that the conjugates can quickly bind on the bacterial surface, irreversibly disrupt the bacterial membrane, and distinctly inhibit intracellular enzyme activity, ultimately leading to the bacterial death. Importantly, these conjugates are highly selective toward bacterial cells over mammalian cells as well as no cytotoxicity to A549 cells and no discernible hemolytic activity. Collectively, this water-soluble galactose-decorated cationic BODIPY-based photodynamic therapy agent design provides promising insights for the development of therapy for antibiotic-resistant bacteria

Single Continuous Near-Infrared Laser-Triggered Photodynamic and Photothermal Ablation of Antibiotic-Resistant Bacteria Using Effective Targeted Copper Sulfide Nanoclusters

The emergence of antibiotic-resistant bacterial strains has made conventional antibiotic therapies less efficient. The development of a novel nanoantibiotic approach for efficiently ablating such bacterial infections is becoming crucial. Herein, a collection of poly­(5-(2-ethyl acrylate)-4-methylthiazole-<i>g</i>-butyl)/copper sulfide nanoclusters (PATA-C4@CuS) was synthesized for efficient capture and effective ablation of levofloxacin-resistant Gram-negative and Gram-positive bacteria upon tissue-penetrable near-infrared (NIR) laser irradiation. In this work, we took advantage of the excellent photothermal and photodynamic properties of copper sulfide nanoparticles (CuSNPs) upon NIR laser irradiation and thiazole derivative as a membrane-targeting cationic ligand toward bacteria. The conjugated nanoclusters could anchor the bacteria to trigger the bacterial aggregation quickly and efficiently kill them. These conjugated nanoclusters could significantly inhibit levofloxacin-resistant Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Bacillus amyloliquefaciens at 5.5 μg/mL under NIR laser irradiation (980 nm, 1.5 W cm^–2, 5 min), which suggested that the heat and reactive oxygen species (ROS) generated from the irradiated CuSNPs attached to bacteria were effective in eliminating and preventing the regrowth of the bacteria. Importantly, the conjugated nanoclusters could promote healing in bacteria-infected rat wounds without nonspecific damage to normal tissue. These findings highlight the promise of the highly versatile multifunctional nanoantibiotics in bacterial infection

Near-Infrared Light-Activated Thermosensitive Liposomes as Efficient Agents for Photothermal and Antibiotic Synergistic Therapy of Bacterial Biofilm

Biofilm is closely related to chronic infections and is difficult to eradicate. Development of effective therapy strategies to control biofilm infection is still challenging. Aiming at biofilm architecture, we designed and prepared near-infrared-activated thermosensitive liposomes with photothermal and antibiotic synergistic therapy capacity to eliminate Pseudomonas aeruginosa biofilm. The liposomes with positive charge and small size aided to enter the biofilm microchannels and locally released antibiotics in infection site. The liposomes could remain stable at 37 °C and release about 80% antibiotics over 45 °C. The biofilm dispersion rate was up to 80%, which was a 7- to 8-fold rise compared to excess antibiotic alone, indicating that the localized antibiotic release and photothermal co-therapy improved the antimicrobial efficiency. In vivo drug-loaded liposomes in treating P. aeruginosa-induced abscess exhibited an outstanding therapeutic effect. Furthermore, photothermal treatment could stimulate the expression of bcl2-associated athanogene 3 to prevent normal tissue from thermal damage. The near-infrared-activated nanoparticle carriers had the tremendous therapeutic potential to dramatically enhance the efficacy of antibiotics through thermos-triggered drug release and photothermal therapy