Encapsulation Of Bacterial Cells Research Articles

Encapsulation of bacterial cells in cytoprotective ZIF-90 crystals as living composites.

Exploiting metal-organic frameworks (MOFs) as selectively permeable shelters for encapsulating engineered cells to form hybrid living materials has attracted increasing attention in recent years. Optimizing the synthesis process to improve encapsulation efficiency (EE) is critical for further technological development and applications. Here, using ZIF-90 and genetically engineered Escherichia coli (E. coli) as a demo, we fabricated E. coli@ZIF-90 living composites in which E. coli cells were encapsulated in ZIF-90 crystals. We illustrated that ZIF-90 could serve as a protective porous cage for cells to shield against toxic bactericides including benzaldehyde, cinnamaldehyde, and kanamycin. Notably, the E. coli cells remained alive and could self-reproduce after removing the ZIF-90 crystal cages in ethylenediaminetetraacetic acid, suggesting a feasible route for protecting and prolonging the lifespan of bacterial cells. Moreover, an aqueous multiple-step deposition approach was developed to improve EE of the E. coli@ZIF-90 composites: the EE increased to 61.9 ± 5.2%, in contrast with the efficiency of the traditional method (21.3 ± 4.4%) prepared with PBS buffer. In short, we develop a simple yet viable strategy to manufacture MOF-based living hybrid materials that promise new applications across diverse fields.

Enhanced biodegradation of hydrocarbons by Pseudomonas aeruginosa-encapsulated alginate/gellan gum microbeads

Pseudomonas aeruginosa-encapsulated alginate/gellan gum microbeads (PAGMs) were prepared at the condition of 10 g/L alginate, 1 g/L gellan gum, and 2.57 mM calcium ions, and investigated for the biodegradation of a diesel-contaminated groundwater. The degradation of diesel with PAGMs reached 71.2% after 10days in the aerobic condition, while that of suspended bacteria was only 32.0% even after 30days. The kinetic analysis showed that PAGMs had more than two-order higher second-order kinetic constant than that of the suspended bacteria. Interestingly, the degradation of diesel was ceased due to the depletion of the dissolved oxygen after 10 day in the PAGM reactor, but the microbial degradation activity was immediately restored after the addition of oxygen to 10.5 mg/L. The change in ATP concentration and the viability of bacteria showed that the microbial activity in PAGMs were maintained (66.4%, and 84.3%, respectively) even after 30days of experiment with PAGMs due to the protective barrier of the microbeads, whereas those of suspended bacteria showed significant decrease to 6.2% and 14.4% of initial value, respectively, due to the direct contact to toxic hydrocarbons. The results suggested that encapsulation of bacterial cells could be used for the enhanced biodegradation of diesel hydrocarbons in aqueous systems.

Bacteria encapsulated electrospun nanofibrous webs for remediation of methylene blue dye in water

In this study, preparation and application of novel biocomposite materials that were produced by encapsulation of bacterial cells within electrospun nanofibrous webs are described. A commercial strain of Pseudomonas aeruginosa which has methylene blue (MB) dye remediation capability was selected for encapsulation, and polyvinyl alcohol (PVA) and polyethylene oxide (PEO) were selected as the polymer matrices for the electrospinning of bacteria encapsulated nanofibrous webs. Encapsulation of bacterial cells was monitored by scanning electron microscopy (SEM) and fluorescence microscopy, and the viability of encapsulated bacteria was checked by live/dead staining and viable cell counting assay. Both bacteria/PVA and bacteria/PEO webs have shown a great potential for remediation of MB, yet bacteria/PEO web has shown higher removal performances than bacteria/PVA web, which was probably due to the differences in the initial viable bacterial cells for those two samples. The bacteria encapsulated electrospun nanofibrous webs were stored at 4°C for three months and they were found as potentially storable for keeping encapsulated bacterial cells alive. Overall, the results suggest that electrospun nanofibrous webs are suitable platforms for preservation of living bacterial cells and they can be used directly as a starting inoculum for bioremediation of water systems.

Stabilization of Lactobacillus reuteri by encapsulation of bacterial cells through spray drying

Micro-organisms are often located within surface-associated multicellular aggregates known as biofilms. The human gastrointestinal tract (GI-tract) carries a microbiota that is constantly affected by extraneous influences, and hence upholding and improving the microbial balance has increased the request for probiotics. Several Lactobacillus reuteri strains have probiotic properties and are used in food technology. In this study the growth characteristics of L. reuteri was investigated using the morphology and stability of L. reuteri ATCC PTA 5289 after encapsulation through spray drying. The bacterial cells were assessed and visualized by Scanning Electron Microscopy (SEM) and Light Microscopy (LM) as well as spectrophotometry. L. reuteri ATCC PTA 5289 showed stable growth on polystyrene surfaces and adherence was also observed on aluminum surfaces. SEM images demonstrated morphological changes of the bacteria that occurred during the spray drying. After spray drying the preparation showed 15 % viable cells. The survival percentage of the spray-dried end product after 4 weeks of storage was approximately 33 % when stored at 5 °C, compared to 5 % at 25 °C.

Bioencapsulation of microbial inoculants for better soil–plant fertilization. A review

Plant fertilization is a major issue in the context of increasing population and food risk, higher cost of fertilizers, and low target efficiency of traditional mineral fertilization practices. Alternatively, application of microbial inoculants to the soil can enhance the uptake of nutrients by plants and increase the efficiency of mineral fertilizers and manures. Encapsulation methods involve covering and protecting the microorganisms. Encapsulation of bacterial cells has been challenged and used mainly in the agricultural industry using processes, such as spray drying, interfacial polymerization, or cross-linking. Here, we review techniques for microbial inoculants and their benefits for sustainable agriculture. Techniques include fluidized bed, extrusion, molecular inclusion, coacervation, liposomes, ionic or inverse gelation, and oil-entrapped emulsion. Major topics discussed are formulation of microbial inoculants, conventional inoculants, bioencapsulation materials, bioencapsulation techniques, and future trends. We found that (1) conventional inoculant does not provide adequate protection for microorganisms. (2) Bioencapsulation improves the protection and controlled release of bacteria. (3) Sodium alginate is one of the most used products for the bioencapsulation of microorganisms. (4) The bioencapsulation of microbial inoculants is performed with the incorporation of an active ingredient into a matrix followed by a mechanical operation, and finally stabilization by a chemical or physical–chemical process. (5) Spray-drying process works on a continuous basis, low operating cost, and high quality of capsules in good yield, although the high temperature used in the process is not very appropriate for encapsulating non-spore-forming bacteria. 6) Fluid-bed process is a promising encapsulation technique for large-scale production in agricultural industry. (7) Ionic gelation is currently the most adequate method found to encapsulate bacteria. (8) Some advantages and drawbacks are found for each technique; therefore, the selection of suitable bioencapsulation method will depend on bacteria strain, cost, processing conditions, and handling.

Comparing phenanthrene degradation by alginate‐encapsulated and free Pseudomonas sp. UG14Lr cells in heavy metal contaminated soils

AbstractBACKGROUND: Many polycyclic aromatic hydrocarbon (PAH) contaminated sites also contain high levels of toxic heavy metals. The presence of heavy metals can adversely affect PAH biodegradation. Encapsulation of bacterial cells has been shown to improve survival and activity of cells under various environmental stresses. This study examined if encapsulation of a phenanthrene‐mineralizing bacterial strain could improve its survival and phenanthrene degradation in heavy metal contaminated soils.RESULTS: Alginate encapsulation did not improve survival and phenanthrene degradation by Pseudomonas sp. UG14Lr in heavy metal contaminated soil. Phenanthrene degradation by, and survival of, free cells and alginate‐encapsulated cells were similar in soil contaminated with 5 mg kg−1 dry soil of As, Cd, or Pb. The number of UG14Lr cells decreased to undetectable level when the concentration of each heavy metal was increased to 100 mg kg−1 dry soil. UG14Lr, when inoculated as free cells, survived the best and they were detected over 60 days of incubation in soil. Cells in both wet and dry alginate beads survived less well than free cells at the higher metal concentrations. Correspondingly, phenanthrene degradation in soil inoculated with free UG14Lr was better than that in soil inoculated with alginate‐encapsulated cells.CONCLUSION: Alginate encapsulation adversely affected the survival and phenanthrene degradation ability of UG14Lr cells in heavy metal contaminated soil. It is postulated that alginate may have concentrated the metals which in turn increased the toxicity to UG14Lr cells. The results are of interest to those interested in the use of encapsulation technology to formulate microbial cells for bioremediation purposes. Copyright © 2009 Society of Chemical Industry

Encapsulation of Bacterial Cells in Electrospun Microtubes

Encapsulation of whole microbial cells in microtubes for use in bioremediation of pollutants in water systems was the main focus of this investigation. Coelectrospinning of a core polymeric solution with bacterial cells and a shell polymer solution using a spinneret with two coaxial capillaries resulted in microtubes with porous walls. The ability of the microtube's structure to support cell attachment and maintain enzymatic activity and proliferation of the encapsulated microbial cells was examined. The results obtained show that the encapsulated cells maintain some of their phosphatase, β-galactosidase and denirification activity and are able to respond to conditions that induce these activities. This study demonstrates electrospun microtubes are a suitable platform for the immobilization of intact microbial cells.

Characterization, morphology and composition of biofilm and precipitates from a sulphate-reducing fixed-bed reactor

The characteristics of the biofilm and the solids formed during the operation of a sulphate-reducing fixed-bed reactor, fed with a moderately acidic synthetic effluent containing zinc and iron, are presented. A diverse population of δ- Proteobacteria SRB, affiliated to four distinct genera, colonized the system. The morphology, mineralogy and surface chemistry of the precipitates were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The XRD patterns observed are characteristic of amorphous solid phases. Peaks corresponding to crystalline iron sulphide, marcasite, sphalerite and wurtzite were also identified. SEM–EDX results confirm the predominance of amorphous phases appearing as a cloudy haze. EDX spectra of spots on the surface of these amorphous phases reveal the predominance of iron, zinc and sulphur indicating the formation of iron and zinc sulphides. The predominance of these amorphous phases and the formation of very fine particles, during the operation of the SRB column, are in agreement and can be explained by the formation pathways of metal sulphides at ambient temperature, alkaline pH and reducing conditions. Solids are precipitated either as (i) amorphous phases deposited on the bed material, as well as on surface of crystals, e.g. Mg 3(PO 4) 2 and (ii) as rod-shaped solids characterized by a rough hazy surface, indicating the encapsulation of bacterial cells by amorphous metal sulphides.

Increase of Viability of Entrapped Cells of Lactobacillus delbrueckii ssp. bulgaricus in Artificial Sesame Oil Emulsions

A technique was developed to protect lactic acid bacteria (Lactobacillus delbrueckii ssp. bulgaricus) against simulated gastrointestinal conditions by encapsulation of bacterial cells within artificial sesame oil emulsions. Purified sesame oil bodies consisting of approximately 99% oil, 0.5% phospholipid, and 0.5% protein were decomposed by heating at 70°C for 1h. The bacteria cultured in nonfat milk were encapsulated in artificial oil emulsions constituted with decomposed sesame oil bodies and excess sesame or vegetable cooking oil. Viability of bacteria in storage at 4°C for 16 d was substantially elevated from 0.023 to 5.45% after encapsulation. Compared with free cells, the entrapped bacteria demonstrated a significant increase (approximately 104 times) in survival rate when subjected to simulated high acid gastric or bile salt conditions. The results indicate that artificial sesame oil emulsion may serve as an effective biocapsule for encapsulation of bacteria in dairy products.