Whole cell entrapment techniques

Optimization of whole-cell bacterial bioreporter immobilization on electrospun cellulose acetate (CA) and polycaprolactone (PCL) fibers for arsenic detection

Arsenic contamination is a critical global problem, and its widespread environmental detection is becoming a prominent issue. Herein, electrospun fibers of cellulose acetate (CA) and polycaprolactone (PCL) were successfully fabricated and used as the support material for immobilization of arsenic-sensing bacterial bioreporter for the first time. To date, no attempt has been made to immobilize fluorescent whole-cell bioreporter cells on electrospun fibers for arsenic detection. CA and PCL electrospun fibers were fabricated via traditional electrospinning technique and characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and contact angle meter. Following immobilization of the bacterial bioreporter cells, the immobilized bacteria were also characterized by viability assay using AlamarBlue. The effects of growth phase and cell concentration on the fluorescence response of fiber-immobilized arsenic bioreporters to arsenic were also investigated. After immobilization of arsenic bioreporters on 10 wt% PCL fiber, 91% of bacterial cells remained viable, while this value was 55.4% for cells immobilized on 12.5 wt% CA fiber. Bioreporter cells in the exponential growth phase were shown to be more sensitive to arsenic compared to aged cells. While both the electropsun PCL- and CA-immobilized bioreporters successfully detected 50 and 100 µg/L of arsenite (As (III)) concentrations, the PCL-immobilized bioreporter showed better fluorescence performance which should be investigated in future studies. This study helps to fill some gaps in the literature and demonstrates the potential for using electrospun fiber-immobilized arsenic whole-cell bioreporter for arsenic detection in water.

Recent Advances in the Biocatalytic Mitigation of Emerging Pollutants: A Comprehensive Review

The issue of environmental pollution has been worsened by the emergence of new contaminants whose morphology is yet to be fully understood. Several techniques have been adopted to mitigate the pollution effects of these emerging contaminants, and bioremediation involving plants, microbes, or enzymes has stood out as a cost-effective and eco-friendly approach. Enzyme-mediated bioremediation is a very promising technology as it exhibits better pollutant degradation activity and generates less waste. However, this technology is subject to challenges like temperature, pH, and storage stability, in addition to recycling difficulty as it is arduous to isolate them from the reaction media. To address these challenges, the immobilization of enzymes has been successfully applied to ameliorate the activity, stability, and reusability of enzymes. Although this has significantly increased the uses of enzymes over a wide range of environmental conditions and facilitated the use of smaller bioreactors thereby saving cost, it still comes with additional costs for carriers and immobilization. Additionally, the existing immobilization methods have their individual limitations. This review provides state-of-the-art information to readers focusing on bioremediation using enzymes. Different parameters such as: the sustainability of biocatalysts, the ecotoxicological evaluation of transformation contaminants, and enzyme groups used were reviewed. The efficacy of free and immobilized enzymes, materials and methods for immobilization, bioreactors used, challenges to large-scale implementation, and future research needs were thoroughly discussed.

Hyperstabilization of a thermophile bacterial laccase and its application for industrial dyes degradation

In the present study, a novel extracellular laccase isolated from Geobacillus stearothermophilus ATCC 10149 was entrapped in a bionanocomposite matrix consisting of copper alginate (Cu-alginate) supplemented with the nanoclay bentonite. After optimization, this nanobiocatalyst was able to degrade up to 90% of Remazol Brilliant Blue R (RBBR) without the addition of redox mediators and retained 70% of its initial activity for at least 1440 h, equivalent to more than 288 uses. The incorporation of nanoclay allowed alginate beads to be used in alkaline pH and strengthened its mechanical properties. Besides, this thermophilic laccase was able to decolorize other structurally different synthetic dyes such as Methyl Orange, Malachite Green and Indigo Carmine. These preliminary results suggested that the nanobiocatalyst could be a suitable option for dye decolorization and be further developed for large scale bioremediation of toxic dyes.

Biotransformation of cladribine by a magnetic immobilizated biocatalyst of Lactobacillus animalis

A stable biocatalyst with magnetic properties based on immobilized Lactobacillus animalis ATCC 35,046 to obtain 2-chloroadenine-2'-deoxyriboside, known as cladribine, is reported for the first time. This nucleoside analogue is an antitumor agent used in the treatment of a wide variety of types of leukemia. In this study, an eco-compatible and alternative bioprocess to obtain cladribine was developed. Product conversion was close to 90% at 2 h in optimized nonconventional reaction media. The microscale biosynthesis of the compound of interest afforded a total productivity close to 370 mg/L/h in the presence of DMSO, and it was stable at least for 30 days in storage conditions.

Biotransformation of cladribine using a stabilized biocatalyst in calcium alginate beads

Cladribine is a nucleoside analogue widely used in the pharmaceutical industry for the treatment of several neoplasms, including hairy-cell leukemia among others. This compound has also shown efficacy in the treatment of autoimmune diseases such as rheumatoid arthritis and multiple sclerosis. In this work, a green bioprocess for cladribine biosynthesis using immobilized Arthrobacter oxydans was developed. The microorganism was stabilized by entrapment immobilization in the natural matrix alginate. Different reaction parameters were optimized obtaining a biocatalyst able to achieve cladribine bioconversion values close to 85% after 1 hr, the shortest reaction times reported so far. The developed bioprocess was successfully scaled-up reaching a productivity of 138 mg L^-1 hr^-1 . Also, the biocatalyst was stable for 5 months in storage and in 96 hr at operational conditions.

Immobilization of E. coli expressing Bacillus pumilus CynD in three organic polymer matrices

Cyanide is toxic to most living organisms. The toxicity of cyanide derives from its ability to inhibit the enzyme cytochrome C oxidase of the electronic transport chain. Despite its high toxicity, several industrial processes rely on the use of cyanide, and considerable amounts of industrial waste must be adequately treated before discharge. Biological treatments for the decontamination of cyanide waste include the use of microorganisms and enzymes. Regarding the use of enzymes, cyanide dihydratase (CynD), which catalyzes the conversion of cyanide into ammonia and formate, is an attractive candidate. Nevertheless, the main impediment to the effective use of this enzyme for the biodegradation of cyanide is the marked intolerance to the alkaline pH at which cyanide waste is kept. In this work, we explore the operational capabilities of whole E. coli cells overexpressing Bacillus pumilus CynD immobilized in three organic polymer matrices: chitosan, polyacrylamide, and agar. Remarkably, the immobilized cells on agar and polyacrylamide retained more than 80% activity even at pH 10 and displayed high reusability. Conversely, the cells immobilized on chitosan were not active. Finally, the suitability of the active complexes for the degradation of free cyanide from a solution derived from the gold processing industry was demonstrated.

Saccharification of citrus wastes by immobilized polygalacturonase in an improved alginate matrix

Enzyme immobilization using hydrogels is a low-cost and effective system for the degradation of bulk pectin derived from orange industry residues. Polygalacturonases obtained from four different bacterial strains of Streptomyces genus were immobilized in alginate gel and assayed for pectin hydrolysis. The enzyme from Streptomyces halstedii ATCC 10897 proved to be superior and more stable within the alginate matrix. Furthermore, a new strategy to improve alginate bead stability using a mixture of calcium and strontium is reported; this technique allowed enhancing the mechanical properties by combining different amounts of these cations for ionotropic gelation. The developed biocatalyst showed maximum hydrolysis at 2 h, generating 1.54 mg/mL of reducing sugars and decreasing the viscosity of polygalacturonic acid by 98.9%. Reusability up to 29 successive reactions (58 h) demonstrated a very stable performance. The heterogeneous biocatalyst was used in the enzymatic saccharification of orange peel albedo (2.23 mg/mL) for adding value to this agro-waste by industrial exploitation.

Immobilization of Microbes for Bioremediation of Crude Oil Polluted Environments: A Mini Review

Petroleum hydrocarbons are the most common environmental pollutants in the world and oil spills pose a great hazard to terrestrial and marine ecosystems. Oil pollution may arise either accidentally or operationally whenever oil is produced, transported, stored and processed or used at sea or on land. Oil spills are a major menace to the environment as they severely damage the surrounding ecosystems. To improve the survival and retention of the bioremediation agents in the contaminated sites, bacterial cells must be immobilized. Immobilized cells are widely tested for a variety of applications. There are many types of support and immobilization techniques that can be selected based on the sort of application. In this review article, we have discussed the potential of immobilized microbial cells to degrade petroleum hydrocarbons. In some studies, enhanced degradation with immobilized cells as compared to free living bacterial cells for the treatment of oil contaminated areas have been shown. It was demonstrated that immobilized cell to be effective and is better, faster, and can be occurred for a longer period.