Mechanism of enhancing pyrene-degradation ability of bacteria by layer-by-layer assembly bio-microcapsules materials.

The mechanism of improving pyrene (PYR)-degrading ability of bacteria CP13 in Layer-by-layer (LBL) assembly chitosan/alginate (CHI/ALG) bio-microcapsules was investigated. Flow cytometry analysis showed that LBL microcapsules could effectively slow down the increasing rate of bacterial cell membrane permeability and the decreasing rate of the membrane potential, so as to reduce the death rate and number of the cells, which could protect the degrading bacteria. The results of Fluorescence spectrum, circular dichroism (CD) spectrum and laser light scattering (LLS) analysis revealed that the other possible mechanism for LBL microcapsules to promote bacterial degradation were following: CHI could enter the secondary structure of the protein of the extracellular polymeric substances (EPS) from CP13 and combined with EPS to generate a stable ground material, which had larger molecular weight (3.76×106 g mol-1) than the original EPS (2.52×106 g mol-1). The combination of CHI and EPS resulted in the decrease of the density of EPS from 1.18 to 0.72 g L-1, suggesting that CHI can loosen the EPS configurations, improving the capture ability of bacteria for PYR as well as the mass transfer of PYR from the extracellular to intracellular, thus eventually promoting the bacteria degrade performance.

Pyrene biodegradation with layer-by-layer assembly bio-microcapsules.

Biotechnology is considered as a promising technology for the removal of polycyclic aromatic hydrocarbons from the environment. Free bacteria are often sensitive to some biotic and abiotic factors in the environment to the extent that their ability to effect biodegradation of organic pollutants, such as polycyclic aromatic hydrocarbons, is hampered. Consequently, it is imperative to carry out investigations into biological systems that will obviate or aid tolerance of bacteria to harsh environmental conditions. Chitosan/alginate bio-microcapsules produced using layer-by-layer (LBL) assembly method were tested for pyrene (PYR) biodegradation under harsh environmental conditions. Morphology observation indicated that the flake bio-microcapsules could be successfully prepared through LBL assembly method. Surface analysis showed that the bio-microcapsules had large fractions of mesopores. The results of the biodegradation experiments revealed that the 95% of 10mgL-1 PYR could be removed by the bacteria encapsulated chitosan/alginate bio-microcapsules in 3 days, which was higher than that of the free bacteria (59%). Compared to the free cells, the bacteria encapsulated chitosan/alginate bio-microcapsules produced 1-6 times higher PYR biodegradation rates at a high initial PYR concentration (50mgL-1) and extremely low pH values (pH =3) or temperatures (10°C or 40°C), as well as high salt stress. The results indicated that bacteria in microcapsules treatment gained a much higher tolerance to environmental stress and LBL bio-microcapsule could be promising candidate for remediating the organic pollutants.

Exploring the mechanism of enhanced Cr(VI) removal by Lysinibacillus cavernae microcapsules loaded with synthetic nano-hydroxyapatite.

In this study, nano-scale hydroxyapatite (HAP) powder was successfully synthesized from waste eggshells and combined with Lysinibacillus cavernae CR-2 to form bio-microcapsules, which facilitated the enhanced removal of Cr(VI) from wastewater. The effects of various parameters, such as bio-microcapsule dosage, HAP dosage, and initial Cr(VI) concentration on Cr(VI) removal, were investigated. Under different treatment conditions, the Cr(VI) removal followed the order of LC@HAP (90.95%) > LC (78.15%) > Free-LC (75.61%) > HAP (6.56%) > NM (0.23%) at the Cr(VI) initial concentration of 50 mg L-1. Relative to other reaction systems, the LC@HAP treatment exhibited a considerable decrease in total Cr content in the solution, with removal rates surpassing 70%. Additionally, the bio-microcapsules maintained significant biological activity after reacting with Cr(VI). Further characterization using SEM, FTIR, XPS, and XRD revealed that the Cr(VI) removal mechanisms by bio-microcapsules primarily involved biological reduction and HAP adsorption. The adsorption of Cr(III) by HAP predominantly occurred through electrostatic interactions and surface complexation, accompanied by an ion exchange process between Cr(III) and Ca(II). Hence, bio-microcapsules, created by combining L. cavernae with HAP, represent a promising emerging material for the enhanced removal of Cr(VI) pollutants from wastewater.

Bioenhanced degradation of toluene by layer-by-layer self-assembled silica-based bio-microcapsules.

In this study, micron-sized monodisperse SiO2 microspheres were used as sacrificial templates, and chitosan/polylactic acid (CTS/PLA) bio-microcapsules were produced using the layer-by-layer (LBL) assembly method. Microcapsules isolate bacteria from their surroundings, forming a separate microenvironment and greatly improving microorganisms' ability to adapt to adverse environmental conditions. Morphology observation indicated that the pie-shaped bio-microcapsules with a certain thickness could be successfully prepared through LBL assembly method. Surface analysis showed that the LBL bio-microcapsules (LBMs) had large fractions of mesoporous. The biodegradation experiments of toluene and the determination of toluene degrading enzyme activity were also carried out under external adverse environmental conditions (i.e., unsuitable initial concentrations of toluene, pH, temperature, and salinity). The results showed that the removal rate of toluene by LBMs can basically reach more than 90% in 2 days under adverse environmental conditions, which is significantly higher than that of free bacteria. In particular, the removal rate of toluene by LBMs can reach four times that of free bacteria at pH 3, which indicates that LBMs maintain a high level of operational stability for toluene degradation. Flow cytometry analysis showed that LBL microcapsules could effectively reduce the death rate of the bacteria. The results of the enzyme activity assay showed that the enzyme activity was significantly stronger in the LBMs system than in the free bacteria system under the same unfavorable external environmental conditions. In conclusion, the LBMs were more adaptable to the uncertain external environment, which provided a feasible bioremediation strategy for the treatment of organic contaminants in actual groundwater.

Enhanced denitrification of sewage via bio-microcapsules embedding heterotrophic nitrification-aerobic denitrification bacteria Acinetobacter pittii SY9 and corn cob.

In this work, bio-microcapsules were prepared by embedding heterotrophic nitrification and aerobic denitrification (HN-AD) bacteria (Acinetobacter Pittii SY9) and corn cob. Bio-microcapsules (20 g/L of corn cob and 30% v/v suspension of strain SY9) were porous (pore size 2579.74-3725.44 nm; porosity 53.6%-79.9%). Under the appropriate conditions (C/N > 2, temperature of 20-35 ℃, rotation speed of 100-120 rpm, pH of 7-9), TN removal efficiency of bio-microcapsules reached 94.4%, and 74.0% of nitrogen was converted into N2. The results of kinetics fitting indicated that aerobic denitrification was the limiting step during HN-AD process. Bio-microcapsules could slow the carbon release of corn cob for 120 days, which ensuring high HN-AD performance even at low C/N of 2.8. Bio-microcapsule SBR could stably run for 88 days with TN removal efficiency > 90% for synthetic sewage. Bio-microcapsules embedding strain SY9 and corn cob have prospective applications for enhancing denitrification of sewage.

Phenanthrene degradation in soil using biochar hybrid modified bio-microcapsules: Determining the mechanism of action via comparative metagenomic analysis.

A strategy involving biochar (BC) hybrid modification was developed to promote the bioremediation effect of degrading bacteria immobilized in layer-by-layer assembly (LBL) microcapsules for the treatment of phenanthrene (PHE) polluted soil. A taxonomic and functional metagenomic approach was used to investigate changes in the microbial community structures and functional gene compositions in the PHE-polluted soil during the bioremediation process. Biofortification with an initial PHE concentration of 100 mg kg-1 dry soil in soils using the BC (3%) hybrid LBL bio-microcapsule (BC-LBL, 2.0 g kg-1 dry soil, 107 colony forming unite cell g-1 dry soil) was faster; further, a higher PHE degradation efficiency (80.5% after 25 d) was achieved when compared with that by the LBL agent (66.2% after 25 d) used. Sphingomonas, Streptomyces, Gemmatirosa, Ramlibacter, Flavisolibacter, Phycicoccus, Micromonospora, Acidobacter, Mycobacterium and Gemmatimonas were more abundant in BC-LBL treatment than those in LBL one. Functional gene annotation results showed that more gene number with BC-LBL treatment than those with LBL one. More abundant functions in the former were primarily related to the growth, reproduction, metabolism, and transportation of bacteria. BC hybridization promoting PHE degradation by microencapsulated bacteria may be due to the strong adsorption property of BC, which results in the enrichment of the nutrients that needed for bacterial growth and reproduction, as well as enhancing the mass transfer performance of PHE to BC-LBL; Meanwhile, BC could also stimulate and improve the metabolism and membrane transportation of the degrading bacteria, and finally improving the degradation function.