Due to their unique structure, poly(amidoamine) (PAMAM) dendrimers have been widely used in medical applications. However, PAMAM dendrimers bearing amino terminals show certain cytotoxicity. In order to improve their biocompatibility, we modified Generation-5 PAMAM dendrimers by conjugating them with poly(ethylene glycol) (PEG) of two different molecular weights and different number of chains. The IC(50) values of PEGylated dendrimers were 12-105 fold higher than those of PAMAM dendrimers. To investigate the influence of PEGylation on PAMAM-induced cytotoxicity, the intracellular responses, reactive oxygen species (ROS) content, mitochondrial membrane potential (MMP), and apoptosis were examined. The results indicated that conjugation with PEG could effectively reduce the PAMAM-induced cell apoptosis by attenuating the ROS production and inhibiting PAMAM-induced MMP collapse. Meanwhile, dendrimers conjugated with less PEG of lower molecular weight did not significantly change the endocytic properties. Dendrimers conjugated with more PEG of higher molecular weight were much less cytotoxic. This study provided a novel insight into the effects of PEGylation on the decrease of cytotoxicity at the molecular level.

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Microbial biofilms can cause severe problems in technical installations where they may give rise to microbially influenced corrosion and clogging of filters and membranes or even threaten human health, e.g. when they infest water treatment processes. There is, hence, high interest in methods to prevent microbial adhesion as the initial step of biofilm formation. In environmental technology it might be desired to enhance bacterial transport through porous matrices. This motivated us to test the hypothesis that the attractive interaction energy allowing cells to adhere can be counteracted and overcome by the shear force induced by electroosmotic flow (EOF, i.e. the water flow over surfaces exposed to a weak direct current (DC) electric field). Applying EOF of varying strengths we quantified the deposition of Pseudomonas fluorescens Lp6a in columns containing glass collectors and on a quartz crystal microbalance. We found that the presence of DC reduced the efficiency of initial adhesion and bacterial surface coverage by >85%. A model is presented which quantitatively explains the reduction of bacterial adhesion based on the extended Derjaguin, Landau, Verwey, and Overbeek (XDLVO) theory of colloid stability and the EOF-induced shear forces acting on a bacterium. We propose that DC fields may be used to electrokinetically regulate the interaction of bacteria with surfaces in order to delay initial adhesion and biofilm formation in technical installations or to enhance bacterial transport in environmental matrices.

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Nanosized plastics (nanoplastics) releasing into the wastewater may pose a potential threat to biological nitrogen removal. Constructed wetland (CW), a wastewater treatment or shore buffer system, is an important sink of nanoplastics, while it is unclear how nitrogen removal in CWs occurs in response to nanoplastics. Here, we investigated the effects of polystyrene (PS) nanoplastics (0, 10, and 1000 μg/L) on nitrogen removal for 180 days in CWs. The results revealed that total nitrogen removal efficiency decreased by 29.5–40.6%. We found that PS penetrated the cell membrane and destroyed both membrane integrity and reactive oxygen species balance. Furthermore, PS inhibited microbial activity in vivo, including enzyme (ammonia monooxygenase, nitrate reductase, and nitrite reductase) activities and electron transport system activity (ETSA). These adverse effects, accompanied by a decline in the relative abundance of nitrifiers (e.g., Nitrosomonas and Nitrospira) and denitrifiers (e.g., Thauera and Zoogloea), directly accounted for the strong deterioration observed in nitrogen removal. The decline in leaf and root activities decreased nitrogen uptake by plants, which is an important factor of deterioration in nitrogen removal. Overall, our results imply that the presence of nanoplastics in the aquatic environment is a hidden danger to the global nitrogen cycle and should receive more attention.

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Ulvan is an important marine polysaccharide. Bacterial ulvan lyases play important roles in ulvan degradation and marine carbon cycling. Until now, only a small number of ulvan lyases have been characterized. Here, a new ulvan lyase, Uly1, belonging to the polysaccharide lyase (PL) family 24 from the marine bacterium Catenovulum maritimum is characterized. The optimal temperature and pH for Uly1 to degrade ulvan are 40°C and pH 9.0, respectively. Uly1 degrades ulvan polysaccharides in the endolytic manner, mainly producing ΔRha3S, consisting of an unsaturated 4-deoxy-L-threo-hex-4-enopyranosiduronic acid and a 3-O-sulfated α-L-rhamnose. The structure of Uly1 was resolved at a 2.10 Å resolution. Uly1 adopts a seven-bladed β-propeller architecture. Structural and site-directed mutagenesis analyses indicate that four highly conserved residues, H128, H149, Y223 and R239, are essential for catalysis. H128 functions as both the catalytic acid and base, H149 and R239 function as the neutralizers, and Y223 plays a supporting role in catalysis. Structural comparison and sequence alignment suggest that Uly1 and many other PL24 enzymes may directly bind the substrate near the catalytic residues for catalysis, different from the PL24 ulvan lyase LOR_107 adopting a two-stage substrate binding process. This study provides new insights into ulvan lyases and ulvan degradation. Importance Ulvan is a major cell wall component of green algae of the genus Ulva. Many marine heterotrophic bacteria can produce extracellular ulvan lyases to degrade ulvan for carbon nutrient. In addition, ulvan has a range of physiological bioactivities based on its specific chemical structure. Ulvan lyase thus plays an important role in marine carbon cycling and has great potential in biotechnological applications. However, only a small number of ulvan lyases have been characterized over the past ten years. Here, based on biochemical and structural analyses, a new ulvan lyase of polysaccharide lyase family 24 is characterized and its substrate recognition and catalytic mechanisms are revealed. Moreover, a new substrate binding process adopted by PL24 ulvan lyases is proposed. This study offers a better understanding of bacterial ulvan lyases and is helpful for studying the application potentials of ulvan lyases.