Showing papers on "Microbial biodegradation published in 2021"

Microbial degradation of recalcitrant pesticides: a review

Abstract: Some pesticides such as organochlorines are of critical environmental concern because they are highly persistent due to their stable chemical nature. As a consequence, even after banning, dichlorodiphenyltrichloroethane and endosulfan can be detected at concentrations above permissible limits. Moreover, classical pesticide degradation of these compounds using physiochemical processes is limited. Alternatively, biodegradation using microorganisms isolated in contaminated sites appears promising. For instance, the bacterium Pseudomonas fluorescens degrades aldrin by 94.8%, and the fungus Ganoderma lucidum can bring down the levels of lindane by 75.5%. In addition, the toxicity is reduced by enzymes that perform oxidation, reduction, hydrolysis, dehydrogenation, dehalogenation and decarboxylation. Then, the metabolites are further degraded by mineralisation and cometabolism. The biodegradation process can be manipulated by applying techniques such as bioattenuation, bioaugmentation and biostimulation. This article discusses the latest advances in microbial degradation of recalcitrant pesticides.

Microbial Degradation of Naphthalene and Substituted Naphthalenes: Metabolic Diversity and Genomic Insight for Bioremediation.

Abstract: Low molecular weight polycyclic aromatic hydrocarbons (PAHs) like naphthalene and substituted naphthalenes (methylnaphthalene, naphthoic acids, 1-naphthyl N-methylcarbamate, etc.) are used in various industries and exhibit genotoxic, mutagenic, and/or carcinogenic effects on living organisms. These synthetic organic compounds (SOCs) or xenobiotics are considered as priority pollutants that pose a critical environmental and public health concern worldwide. The extent of anthropogenic activities like emissions from coal gasification, petroleum refining, motor vehicle exhaust, and agricultural applications determine the concentration, fate, and transport of these ubiquitous and recalcitrant compounds. Besides physicochemical methods for cleanup/removal, a green and eco-friendly technology like bioremediation, using microbes with the ability to degrade SOCs completely or convert to non-toxic by-products, has been a safe, cost-effective, and promising alternative. Various bacterial species from soil flora belonging to Proteobacteria (Pseudomonas, Pseudoxanthomonas, Comamonas, Burkholderia, and Novosphingobium), Firmicutes (Bacillus and Paenibacillus), and Actinobacteria (Rhodococcus and Arthrobacter) displayed the ability to degrade various SOCs. Metabolic studies, genomic and metagenomics analyses have aided our understanding of the catabolic complexity and diversity present in these simple life forms which can be further applied for efficient biodegradation. The prolonged persistence of PAHs has led to the evolution of new degradative phenotypes through horizontal gene transfer using genetic elements like plasmids, transposons, phages, genomic islands, and integrative conjugative elements. Systems biology and genetic engineering of either specific isolates or mock community (consortia) might achieve complete, rapid, and efficient bioremediation of these PAHs through synergistic actions. In this review, we highlight various metabolic routes and diversity, genetic makeup and diversity, and cellular responses/adaptations by naphthalene and substituted naphthalene-degrading bacteria. This will provide insights into the ecological aspects of field application and strain optimization for efficient bioremediation.

Aerobic and Anaerobic Bacterial and Fungal Degradation of Pyrene: Mechanism Pathway Including Biochemical Reaction and Catabolic Genes.

Abstract: Microbial biodegradation is one of the acceptable technologies to remediate and control the pollution by polycyclic aromatic hydrocarbon (PAH). Several bacteria, fungi, and cyanobacteria strains have been isolated and used for bioremediation purpose. This review paper is intended to provide key information on the various steps and actors involved in the bacterial and fungal aerobic and anaerobic degradation of pyrene, a high molecular weight PAH, including catabolic genes and enzymes, in order to expand our understanding on pyrene degradation. The aerobic degradation pathway by Mycobacterium vanbaalenii PRY-1 and Mycobactetrium sp. KMS and the anaerobic one, by the facultative bacteria anaerobe Pseudomonas sp. JP1 and Klebsiella sp. LZ6 are reviewed and presented, to describe the complete and integrated degradation mechanism pathway of pyrene. The different microbial strains with the ability to degrade pyrene are listed, and the degradation of pyrene by consortium is also discussed. The future studies on the anaerobic degradation of pyrene would be a great initiative to understand and address the degradation mechanism pathway, since, although some strains are identified to degrade pyrene in reduced or total absence of oxygen, the degradation pathway of more than 90% remains unclear and incomplete. Additionally, the present review recommends the use of the combination of various strains of anaerobic fungi and a fungi consortium and anaerobic bacteria to achieve maximum efficiency of the pyrene biodegradation mechanism.

Biodegradation of fipronil: current state of mechanisms of biodegradation and future perspectives

Abstract: Fipronil is a broad-spectrum phenyl-pyrazole insecticide that is widely used in agriculture. However, in the environment, its residues are toxic to aquatic animals, crustaceans, bees, termites, rabbits, lizards, and humans, and it has been classified as a C carcinogen. Due to its residual environmental hazards, various effective approaches, such as adsorption, ozone oxidation, catalyst coupling, inorganic plasma degradation, and microbial degradation, have been developed. Biodegradation is deemed to be the most effective and environmentally friendly method, and several pure cultures of bacteria and fungi capable of degrading fipronil have been isolated and identified, including Streptomyces rochei, Paracoccus sp., Bacillus firmus, Bacillus thuringiensis, Bacillus spp., Stenotrophomonas acidaminiphila, and Aspergillus glaucus. The metabolic reactions of fipronil degradation appear to be the same in different bacteria and are mainly oxidation, reduction, photolysis, and hydrolysis. However, the enzymes and genes responsible for the degradation are somewhat different. The ligninolytic enzyme MnP, the cytochrome P450 enzyme, and esterase play key roles in different strains of bacteria and fungal. Many unanswered questions exist regarding the environmental fate and degradation mechanisms of this pesticide. The genes and enzymes responsible for biodegradation remain largely unexplained, and biomolecular techniques need to be applied in order to gain a comprehensive understanding of these issues. In this review, we summarize the literature on the degradation of fipronil, focusing on biodegradation pathways and identifying the main knowledge gaps that currently exist in order to inform future research. KEY POINTS: • Biodegradation is a powerful tool for the removal of fipronil. • Oxidation, reduction, photolysis, and hydrolysis play key roles in the degradation of fipronil. • Possible biochemical pathways of fipronil in the environment are described.

Bioremediation of Pesticides: An Eco-Friendly Approach for Environment Sustainability

Abstract: Various pesticides including organochlorines, organophosphates, carbamate, pyrethroids, chloronicotinyl etc., are used in agriculture for protection against plant diseases and insects. Only a fraction of the applied pesticides is utilized in killing of target pests and the leftover residual pesticides either remains associated with cereal grains, vegetables, and fruits or may cause environmental pollution. In addition to the traditional physical and chemical degradation methods, the microbial degradation method is commonly more efficient and low-cost method used for pesticide degradation. Microorganisms have been characterized which have the capability to degrade residual pesticides. The microbes that demolish these pesticides use the pesticides as nutrients and break them down into tiny nontoxic molecules. Pesticide degrading microbes belong to different microbial groups, i.e., bacteria, fungi, actinomycetes, and algae. Bacteria possessing pesticide degradation capability include Pseudomonas spp., Bacillus spp., Burkholderia, Klebsiella spp., Streptomyces, etc. and the fungi include Trichoderma spp., Aspergillus spp., Phanerochaete chrysosporium, white rot fungi, etc., whereas algae include Chlamydomonas and marine Chlorella. Major reactions in pesticide destruction include mineralization and co-metabolism. Pesticide degradation is influenced by many factors such as type of pesticide, type of microorganism, temperature, humidity, and acidity in the environment. Plasmid-located genes usually encode many enzymes and degrade a large number of pesticides. Microorganisms may acquire pesticide-degradation capabilities in soil through horizontal gene transfer from degradative plasmids, by modification of substrate specificity, or through altered regulation of preexisting enzymes. With the progress of molecular biology, the genetically engineered rhizobacteria may be built to enhance the bioremediation of pollutants and pesticides. Such recombinant microbial populations may be of immense value in bioremediation of diverse pesticides from the surroundings.

Microbe-based bioreactor system for bioremediation of organic contaminants: present and future perspective

Abstract: In past few decades, environmental pollution has been increased because of human activities. Pollutants have toxic effects on human health and environment. Thus remediation of these pollutants is required to clean up the surroundings and reducing the health hazardous risk. Bioremediation is an environment-friendly process to clean pollutants from the surroundings. In this process, pollutants are converted into less toxic or environment-friendly compounds by microbes. Microbial remediation can be applied ex situ or in situ conditions. However, in situ bioremediation is a slow process that is difficult to optimize and control. To resolve these issues, bioreactors are developed. Bioreactors provide optimum condition for the growth of microorganisms, and microbial biodegradation mechanisms are used in the bioremediation processes to accomplish the desired remediation targets. Bioreactors have a different mode of operations such as batch, fed batch, and continuous with a range of designs, including slurry-phase, partitioning, stirred-tank, biofilters, bioscrubbers, trickle-bed, fluidized-bed, packed-bed, airlift, and membrane bioreactor. This chapter provides more insight into the major bioreactors, their design, advantages, and limitations.

Enhanced Hydrocarbons Biodegradation at Deep-Sea Hydrostatic Pressure with Microbial Electrochemical Snorkels

Abstract: In anaerobic sediments, microbial degradation of petroleum hydrocarbons is limited by the rapid depletion of electron acceptors (e.g., ferric oxide, sulfate) and accumulation of toxic metabolites (e.g., sulfide, following sulfate reduction). Deep-sea sediments are increasingly impacted by oil contamination, and the elevated hydrostatic pressure (HP) they are subjected to represents an additional limitation for microbial metabolism. While the use of electrodes to support electrobioremediation in oil-contaminated sediments has been described, there is no evidence on their applicability for deep-sea sediments. Here, we tested a passive bioelectrochemical system named ”oil-spill snorkel” with two crude oils carrying different alkane contents (4 vs. 15%), at increased or ambient HP (10 vs. 0.1 MPa). Snorkels enhanced alkanes biodegradation at both 10 and 0.1 MPa within only seven weeks, as compared to nonconductive glass controls. Microprofiles in anaerobic, contaminated sediments indicated that snorkels kept sulfide concentration to low titers. Bulk-sediment analysis confirmed that sulfide oxidation by snorkels largely regenerated sulfate. Hence, the sole application of snorkels could eliminate a toxicity factor and replenish a spent electron acceptor at increased HP. Both aspects are crucial for petroleum decontamination of the deep sea, a remote environment featured by low metabolic activity.

Microbial degradation of organic pollutants using indigenous bacterial strains

Abstract: From the last century where world has gotten the ease of living due to the globalization and industrial revolution, these have given the global population, a nuisance, pollution. Many factors have contributed to the increased pollution and its adverse effects on planet Earth, for instance, uncontrolled anthropogenic activities, unwise use of petroleum products, emission and poor waste managements of industrial waste, release of toxic organic by-products, increased use of pesticides, insecticides, and fertilizers. Hydrocarbons or organic compounds are known to be the potential carcinogens and toxins for almost all forms of life. Many strategies have been proposed and implemented to degrade the organic pollutants and proper disposal of industrial waste, but some of them either are not applicable or have failed to generate the desired results. From the last few decades, researches are interested to find a biological way of degrading the complex organic pollutants, which is also known as bioremediation. Many species of microbes have been isolated from the polluted indigenous areas that are proven to degrade the toxic, complex organic compounds that can be used in practical biodegradation of contaminated areas, that is, soil and water at large scale. This chapter comprises the important aspects of isolating effective microbial indigenous species, involvement of factors, that is, distribution of pollutants in soil matrix; physiological parameters affecting efficacy of biodegradation; improvement of the inherent property of microbes to biodegrade highly complex pollutants, for example, hydrocarbons and phenolic compounds; effects of inhibitors on biodegradation of organic contaminants; implementation of the biodegrading microbial flora in different environment, and success on complete mineralization of organic pollutants.