Modulation of a Loop Region in the Substrate Binding Pocket Affects the Degree of Polymerization of Bacillus subtilis Chitosanase Products.

The hydrolytic products of chitosanase from Streptomyces avermitilis (SaCsn46A) were found to be aminoglucose and chitobiose, whereas those of chitosanase from Bacillus subtilis (BsCsn46A) were chitobiose and chitotriose. Therefore, the sequence alignment between SaCsn46A and BsCsn46A was conducted, revealing that the structure of BsCsn46A possesses an extra loop region (194N-200T) at the substrate binding pocket. To clarify the impact of this loop on hydrolytic properties, three mutants, SC, TJN, and TJA, were constructed. Eventually, the experimental results indicated that SC changed the ratio of chitobiose to chitotriose hydrolyzed by chitosanase from 1:1 into 2:3, while TJA resulted in a ratio of 15:7. This experiment combined molecular research to unveil a crucial loop within the substrate binding pocket of chitosanase. It also provides an effective strategy for mutagenesis and a foundation for altering hydrolysate composition and further applications in engineering chitosanase.

Physicochemical and biological changes on naturally aged microplastic surfaces in real environments over 10 months.

Microplastics (MPs) undergo aging over time, which can influence their behavior in the environment. While laboratory-simulated studies have investigated MP aging, research on natural aging in various real environments remains limited. This study aims to investigate the physical, chemical and biological changes that occur in five types of MPs after more than 10 months of natural aging in three different real environments: seawater, air and soil. Results are compared with previous laboratory experiments. The surface roughness of all types of aged MPs was found to be higher in seawater than in air and soil, which differed from previous simulated studies that showed the highest roughness in air. All aged MPs exhibited the occurrence of hydroxyl and carbonyl groups due to the oxidation processes. Interestingly, the MPs aged in soil showed the lowest level of these functional groups, while in seawater or air, some MPs demonstrated the highest. This contrasts with previous studies indicating the highest level of oxygen-containing functional groups in aged MPs in air. Bacterial analysis identified fourteen bacterial phyla on the surface of aged MPs in all three real environments, with varying abundance in specific environments. Notably, the composition of bacterial communities in the microplastisphere was determined by the surrounding environments, independent of MP types. Natural aging is more complex than laboratory simulations, and the degree of MP aging increases with the complexity of environmental factors. These findings enhance our understanding of the natural aging of MPs in different real environments.

Microplastisphere may induce the enrichment of antibiotic resistance genes on microplastics in aquatic environments: A review.

Microplastics have been proven to be hotspots of bacterial pathogens and antibiotic resistance genes (ARGs). The enrichment of ARGs in microplastisphere, the specific niche for diverse microbial communities attached to the surface of microplastic, has attracted worldwide attention. By collecting 477 pairs of ARG abundance data belonging to 26 ARG types, based on the standardized mean difference (SMD) under the random effect model, we have performed the first meta-analysis of the ARG enrichment on microplastics in aquatic environments in order to quantitatively elucidate the enrichment effect, with comparison of non-microplastic materials. It was found that ARGs enriched on the microplastics were more abundant than that on the inorganic substrates (SMD = 0.26) and natural water environments (SMD = 0.10), but lower abundant than that on the natural organic substrates (SMD = -0.52). Furthermore, microplastics in freshwater tended to have a higher degree of ARG enrichment than those in saline water and sewage. The biofilm formation stage, structure, and component of microplastisphere may play a significant role in the enrichment of ARGs.

Smoking related environmental microbes affecting the pulmonary microbiome in Chinese population.

BACKGROUND: Smoking is a serious public health problem that affects human health conditions. Although there is evidence that microorganisms are associated with smoking-related lung diseases, the relationship between the rich lung microbiome of upper respiratory tract groups and smoking has not been studied. OBJECTIVE: In this study, we investigated the effects of smoking on environmental microbes and lung microbiome in the Chinese population and provided clues for the role of smoking in the development of respiratory disease. METHODS: Bronchoalveolar lavage fluid samples were collected from 55 individuals with a history of smoking. Microbial gene sequencing was carried out through NGS technology. We analyzed and compared the diversity, community structure, and species abundance of bronchoalveolar lavage microbiome between smokers and nonsmokers, to speculate the effects of smoking on the lung microbiome. RESULTS: Smoking hardly affected the α diversity of microbial groups of bronchoalveolar lavage, but it had a huge influence on the microbiome composition. The relative abundance of Rothia, Actinomycetes, Haemophilus, Porphyrins, Neisseria, Acinetobacter, and Streptococcus genera had a remarkable increase in the smoking group. On the other hand, the relative abundance of Plusella and Veronella decreased significantly. CONCLUSION: Smoking may change the environmental microbes and then alter the structure of the lung microbiome, which may lead to smoking-related diseases.

Quantum tunneling effect on the surface enhanced Raman process in molecular systems.

In this paper, we theoretically study the effect of quantum tunneling on the surface enhanced Raman scattering (SERS) of a generic molecule confined in sub-nanometer nanocavities formed by metallic dimers. The tunneling effect was described by the quantum corrected model in combination with finite element simulations. The SERS spectra were calculated by a density matrix method. Simulation results demonstrate that both the field enhancement and the molecular SERS spectra are very sensitive to the size of the cavity. By decreasing the gap size, the local field enhancement first increases then starts to be significantly suppressed as a result of the tunneling effect which neutralizes the positive and negative induced charges in the nanocavity. Consequently, the SERS intensity also experienced dramatic decrease in the short gap distance region. We also show that both the plasmonic enhancement to the local field and the enhanced molecular decay rates have to be taken into account to understand the SERS properties of the molecule in such sub-nanometer nanocavities. These results could be helpful for the understanding of the surface enhanced spectral properties of molecular systems at sub-nanometer nanocavities.

Rapid detection of biodegradable organic matter in polluted water with microbial fuel cell sensor: Method of partial coulombic yield.

The quantification of biodegradable organic matter (BOM) in polluted water plays an essential role for biodegradation-based processing of wastewater and management of water environment. Compared with the traditional detection of five-day biochemical oxygen demand (BOD5), microbial fuel cell (MFC) sensors have shown an advantage for rapid and more accurate BOM assessment in several hours using coulombic yield of MFC as the signal. In this study, we propose a new calculation method that relies on the partial coulombic yield (P-CY) to further shorten the duration of the measurement. The P-CY is the cumulative coulomb at the point at which the voltage acquisition reaches a maximum voltage drop rate. The detection results with the standard GGA solution (a mixture of glucose and glutamic acid) show an enhanced linear relationship ranging from 37.5 mg L-1 to 375 mg L-1 in comparison to conventional methods. Notably, the response time for P-CY is remarkably shortened (0.99 ± 0.18-18.08 ± 0.58 h). The cutoff point for P-CY has more stable electrochemical characteristics, which enhances the accuracy of BOM detection. Furthermore, the validity of our determination of the cutoff point for P-CY is demonstrated by a mathematical model based on the Michaelis-Menten equation. Thus, the P-CY method is viable for the rapid detection of BOM in polluted water.

Different factors determined the toxicokinetics of organic chemicals and nanomaterials exposure to zebrafish (Danio Rerio).

Little is known about how the chemical properties (molecular structure, such as the hydrophobic and hydrophilic end group for organic chemical, and particle size for nanomaterials (NMs)) quantitatively affect the toxicokinetics (TK) in organisms especially in short-term, single-species studies. A novel method based on a first-order one compartment TK model which described the monophasic uptake pattern and two-compartment TK model which adequately described the biphasic metabolism pattern was used to determine the bioconcentration and TK rate constants of organic compounds (n = 17) and nanomaterials (NMs, n = 7) in zebrafish. For both one and two compartment model, the uptake (kin) and elimination (kout) rate constants were fitted using a one- and two-compartment first-order kinetic model, and bioconcentration factors (BCF) and 95% depuration times (t95) for all tested chemicals were calculated, respectively. The results showed that there was significant difference in TK parameters kin, kout, and BCF between organic chemicals and nano metal oxides. For organic compounds, significant correlations were found between the kin and BCF and the octanol-water partition coefficient (Kow) and molecular mass. For nano metal oxides, there was a significant negative correlation between the kin or BCF and particle size, but a positive correlation between kin and Zeta potential of nanoparticles and also a significant positive correlation between kout and particle size or specific surface area. Those findings indicated that NMs particle size does matter in biological influx and efflux processes. Our results suggest that the TK process for organic compound and NMs are correlated by different chemical properties and highlight that the Kow, the absorption kin, metabolism k12 and k21, elimination rate kout, and all the parameters that enable the prediction and partitioning of chemicals need to be precisely determined in order to allow an effective TK modeling. It would therefore appear that the TK process of untested chemicals by a fish may be extrapolated from known chemical properties.

Predicting the survival of zebrafish larvae exposed to fluctuating pulses of lead and cadmium.

Aquatic organisms are often exposed to time-varied concentrations of contaminants due to pulsed inputs in natural water. Traditional toxicology experiments are usually carried out in a constant exposure pattern, which is inconsistent with the actual environment. In this study, a refined toxicokinetic-toxicodynamic (TK-TD) model was used to study the toxic effects of Pb and Cd on zebrafish larvae under three pulse exposures with 2, 4, and 6 h, respectively. The parameter sensitivity analysis showed that JM, max had the greatest impact on the output of the model. Cd or Pb pulse exposure resulted in less death than constant exposure at the same time-weighted average (TWA) concentrations. Survival fraction in larvae under 6 h interval between two pulses of Pb or Cd was larger than that under 2 h and 4 h interval. Toxicity under constant exposure of Cd or Pb was greater than that under 2, 4, and 6 h interval pulse exposure because the cumulative Cd or Pb concentration in the body under constant exposure was greater than that under pulse exposure. The results also showed that the stochastic death (SD) model was more suitable than the individual tolerance (IT) model for predicting the survival fraction of larvae under pulse exposure to Pb and Cd, which was indicated by higher R2 (0.670-0.940) in SD model than that (0.588-0.861) in IT model. Our model provides approaches for laboratory toxicity testing and modeling approaches for addressing the toxicity of heavy metal pulsed exposure.