Bioremediation is traditionally carried out using ‘free’ bacterial cells; however, in recent years, utilization of ‘immobilized’ bacterial cells has gained attention as a promising technique due to multifarious benefits. This review collates a vast amount of existing literature on the myriad contaminants treated using immobilized bacteria. We also discuss various mechanistic aspects of using immobilized cells for environmental remediation applications, with special attention on cells encapsulated in hydrogels and their implementation in detoxifying harmful contaminants and environmental cleanup. We examine different methods/techniques for immobilizing viable bacterial cells in various supporting matrices, use of single- and multi-species bacterial communities, various growth substrates, and factors affecting the remediation process including mass transfer, kinetic processes and bioreactor configurations used in pilot and field-scale applications. The advantages and limitations associated with the use of immobilized bacteria in a bioreactor for contaminated water treatment are also discussed. From a sustainable futures perspective, resource recovery and retrieval of value-added products along with bioremediation could be an added benefit of the immobilized cell-based treatment system, making it a more cost-effective and viable treatment strategy as well as one that is amenable to the principles of circular economy.

Use of immobilized bacteria for environmental bioremediation: A review

Recent advances in structural modifications of photo-catalysts for organic pollutants degradation - A comprehensive review.

Bioremediation is a key process for reclaiming polluted soil and water by the use of biological agents. A commonly used approach aims to neutralise or remove harmful pollutants from contaminated areas using live microorganisms. Generally, immobilised microorganisms rather than planktonic cells have been used in bioremediation methods. Activated carbon, inorganic minerals (clays, metal oxides, zeolites), and agricultural waste products are acceptable substrates for the immobilisation of bacteria, although there are limitations with biomass loading and the issue with leaching of bacteria during the process. Various synthetic and natural polymers with different functional groups have been used successfully for the efficient immobilisation of microorganisms and cells. Promise has been shown using macroporous materials including cryogels with entrapped bacteria or cells in applications for water treatment and biotechnology. A cryogel is a macroporous polymeric gel formed at sub-zero temperatures through a process known as cryogelation. Macroporous hydrogels have been used to make scaffolds or supports for immobilising bacterial, viral, and other cells. The production of composite materials with immobilised cells possessing suitable mechanical and chemical stability, porosity, elasticity, and biocompatibility suggests that these materials are potential candidates for a range of applications within applied microbiology, biotechnology, and research. This review evaluates applications of macroporous cryogels as tools for the bioremediation of contaminants in wastewater.

Polymeric Materials Used for Immobilisation of Bacteria for the Bioremediation of Contaminants in Water.

Enhanced bioremediation of 2,3',4,4',5-pentachlorodiphenyl by consortium GYB1 immobilized on sodium alginate-biochar.

The purpose of this present study was to reduce the pollution load of the tannery effluent through a cell immobilization approach using chromium tolerant bacteria isolated from tannery sludge. Among various initially isolated bacteria, strain IITR002 exhibited the highest pollution load reduction was characterized as Ochrobactrum intermedium by 16S rDNA sequencing. The bacterium was successfully immobilized with 10 % polyvinyl alcohol (PVA) and 1% sodium alginate (SA) and tannery effluent treatment were carried out using both free and immobilized cells of O. intermedium. Preliminary chemical oxygen demand (COD) reduction studies demonstrated 85 % and 54 % COD reductions by immobilized and free cells, respectively as compared to blank PVA beads (10 % COD). Both free and immobilized cells were able to degrade tannery effluent after 48 h but the reduction of total dissolved solids-TDS (56 %), COD (85 %), biochemical oxygen demand-BOD (68 %), and total chromium-TC (95 %) were higher with immobilized cells. The reduction of pollutants in tannery effluent was established by GC–MS analysis in which degradation of organic pollutants after treating with free and immobilized cells was observed. Phytotoxicity investigation of tannery effluents on Vigna radiata L seed showed that bacterial treatment not only allowed seeds germination but also supported seedling growth. The results from this flask-scale work suggest that immobilized cell methods of bacterial treatment can potentially be applied in tannery effluent treatment to reduce the pollution load as well as phytotoxic effects.

Reduction of pollution load of tannery effluent by cell immobilization approach using Ochrobactrum intermedium

A new approach for easy synthesis of Bacillus pseudomycoides immobilized polyvinyl alcohol (PVA)/glutaraldehyde (GA) hydrogel for application in a wastewater treatment system is reported. Optimization studies revealed that GA/PVA mass ratio of 0.03 and acidic pH of 2 were required for hydrogel synthesis and eventually for bacterial cell immobilization. The synthesized crosslinked matrix possessed a pore size suitable for microbial cell entrapment while maintaining cell accessibility to external environment for bioremediation. Possible crosslinking and bacterial cell immobilization in the hydrogel were evidenced by FTIR, XRD, and SEM studies, respectively. Further, the extent of crosslinking of GA with PVA was investigated and confirmed by transmittance and permeability experiments. The viability and proliferation of hydrogel embedded cells (after 25 days) was confirmed by confocal fluorescence microscopy which also indicated that acidic pH of polymer solution did not affect the immobilized live cells. B. pseudomycoides immobilized hydrogel were demonstrated to be effective for treatment of municipal wastewater and reduced biochemical oxygen demand (BOD), chemical oxygen demand (COD), and protein content below the recommended levels. Overall, the results from this bench-scale work show that employing bacteria-embedded PVA/GA hydrogel for the treatment of municipal wastewater yield promising results which should be further explored in pilot/field-scale studies.

Rapid immobilization of viable Bacillus pseudomycoides in polyvinyl alcohol/glutaraldehyde hydrogel for biological treatment of municipal wastewater

Introduction: Even after many months, the highly contagious and infectious SARS-CoV-2 virus that caused a pandemic in the year 2020 is still thriving. The identification of the effective drug against this virus is the need of the hour. This highly infectious virus, upon entry into the host, binds to the cellular Angiotensin-converting enzyme 2 (ACE2) with the aid of spike protein. Thus, both of these proteins represent a potential therapeutic target for inhibiting the interaction between the two. This study utilizes the in silico approach to identify compounds that can inhibit the interaction of the spike protein of the SARS-CoV-2 and ACE2. The study investigated plant-derived medicinal compounds and the two compounds and their derivatives (Arjunolic acid, Noscapine) based on their anti-viral properties. Methodology and tools used: Using molecular docking techniques, the binding affinity of the compounds with the protein targets were measured, and then the results were analyzed by building the interaction plots and mapping the binding residues on the interface of the interaction. The methodology used was carried out using AUTODOCK Vina 1.1.2, PyMOL, and LigPlot Plus v 2.2. Results: The results indicate that out of 40 compounds used in this study, Withanolide, Arjunolic Acid, Calceolarioside, and Amaranthin Betacyanin had a high affinity for the spike protein, ACE2 and the molecular complex of both (spike protein of SARS-CoV-2 and ACE2). Conclusion: In conclusion, all these identified compounds have the potential to disrupt the binding of the spike protein and ACE2 as well as carry an additional advantage of imparting relief in symptoms and may be investigated for further research to find a cure.

Mohammad Nawaid Zaman

Papers

Rapid immobilization of viable Bacillus pseudomycoides in polyvinyl alcohol/glutaraldehyde hydrogel for biological treatment of municipal wastewater

In Silico Analysis of Plant-Derived Medicinal Compounds Against Spike Protein of SARS-CoV-2 and Ace2