Bioremediation

Bioremediation

Heavy metal resistance in Thlaspi caerulescens is due to:

Heavy metal resistance in Thlaspi caerulescens now Noccaea caerulescens, model zinc and cadmium hyperaccumulator thriving on calamine metalliferous soils with percent ore, relies on enhanced active efflux and compartmentalization minimizing cytosolic toxicity rather than metabolism. Central actors are P1B-type ATPases: HMA3 tonoplast localized sequestering Cd and Zn into leaf vacuoles with 100-fold higher capacity than non-accumulator due to triplication and cis-regulatory mutations driving constitutive overexpression 50 to 100 times, and HMA4 plasma membrane in root pericycle driving efflux i

Ref: Assunção et al. New Phytologist 2003 HMA gene family overexpression; Papoyan & Kochian Plant Physiology 2004 Cd ATPase; Nature Plants 2016 hyperaccumulation mechanism.

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Bioremediation

Which plant family is extensively used for phytoremediation?

Brassicaceae also called Cruciferae mustard family dominates phytoremediation literature due to hyperaccumulation capacity, rapid growth biomass 5 to 20 tons per hectare, high seed production and genetic tractability with Arabidopsis thaliana as model enabling molecular characterization. Genera include Thlaspi caerulescens now Noccaea accumulating zinc up to 30,000 and cadmium 3,000 mg per kg, Brassica juncea for lead up to 10,000, selenium, chromium and uranium, Alyssum bertolonii and murale hyperaccumulating nickel above 10,000 mg per kg in serpentine soils, and Brassica napus for radionucli

Ref: Baker 1997 Brassicaceae hyperaccumulators New Phytol; Peer et al. 2006 Brassica phytoremediation Plant Biology; EPA Brassicaceae plant family guide.

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Bioremediation

Phytovolatilization involves:

Phytovolatilization constitutes specialized phytoremediation pathway where selected plants absorb contaminants that are volatile in their native form or can be enzymatically transformed into volatile derivatives, translocate upward via xylem driven by transpiration pull generating negative pressure minus 1 to 2 MPa, and release through stomatal conductance into atmosphere as less toxic gaseous species. Classic illustrations include selenium taken up as selenate via sulfate transporters Sultr in Brassica juncea, metabolized through cysteine synthase to selenocysteine, methylated by selenocystei

Ref: Pilon-Smits 2005 Selenium volatilization; Terry et al. Environmental Science Technology selenium; EPA phytovolatilization evaluation.

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Bioremediation

Phytostabilization results in:

Phytostabilization aims to reduce mobility and bioavailability of heavy metals not readily degradable without removing mass, establishing persistent vegetative cover immobilizing pollutants in root zone and preventing off-site migration via wind or water. Tolerant grasses Festuca rubra, Agrostis stolonifera and Buchloe dactyloides plus legumes fix nitrogen achieve stabilization through raising rhizosphere pH via carbonates causing precipitation as hydroxides and phosphates, stimulating sulfate-reducing Desulfovibrio producing sulfide precipitating PbS and ZnS with Ksp 10^-28, binding to root c

Ref: Mendez & Maier Phytostabilization of mine tailings 2008 Environmental Health; EPA phytostabilization guidance 2000; PubMed immobilization mechanisms.

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Bioremediation

Rhizofiltration is mainly used for removal of contaminants from:

Rhizofiltration specifically uses plant root systems grown hydroponically in greenhouse to develop extensive fibrous mass before transfer to contaminated water to filter, adsorb and absorb contaminants from groundwater, effluents and radioactive ponds. Dense mats of sunflower Helianthus annuus accumulating uranium and cesium, Indian mustard Brassica juncea removing lead and chromium, and bulrush Scirpus for selenium provide 10 to 20 square meters surface per plant coated with mucilage and biofilm containing phytochelatins that precipitate and chelate metals via ion exchange. Mechanism involves

Ref: Dushenkov et al. Environmental Science Technology 1995 Rhizofiltration of radionuclides; EPA Rhizofiltration overview; PubMed water phytoremediation 1997.

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Bioremediation

Phytoextraction refers to:

Phytoextraction also termed phytoaccumulation focuses on removal of inorganics heavy metals nickel, zinc, cadmium, lead and metalloids arsenic and selenium from soils via plant uptake into harvestable shoots. Hyperaccumulators Alyssum bertolonii accumulating nickel up to 10,000 mg per kg, Thlaspi caerulescens Noccaea concentrating zinc above 30,000, Brassica juncea for lead achieve concentrations 10 to 500 times soil via high-affinity transporters ZIP ZNT1 and HMA ATPase, chelation with citrate, malate, histidine and sequestration in leaf vacuoles via MTP1 and HMA3. Shoots harvested at floweri

Ref: Baker & Brooks 1989 Terrestrial higher plants hyperaccumulation; Chaney et al. Current Opinion Biotechnology 1997 phytoextraction; EPA extraction guidance.

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Bioremediation

Phytoremediation uses:

Phytoremediation integrates botanical processes with rhizosphere microbial ecology for contaminant removal, transformation, containment or detoxification using living plants and their associated microbiome. Roots actively exude low-molecular-weight organic acids such as citrate, malate, oxalate, sugars like glucose, amino acids and flavonoids that function as chemoattractants recruiting plant-growth-promoting rhizobacteria including Rhizobium, Pseudomonas fluorescens, Burkholderia and mycorrhizal fungi like Glomus that colonize root surface and interior, forming beneficial biofilm carrying cat

Ref: Pilon-Smits Phytoremediation Annual Review Plant Biology 2005; EPA Phytoremediation overview 2000; PubMed plant-microbe interaction.

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Bioremediation

Which bacterium is resistant to radiation and used in bioremediation of nuclear waste?

Deinococcus radiodurans, Gram-positive tetrad-forming non-sporulating bacterium isolated from gamma-irradiated canned meat, holds world record for ionizing radiation resistance surviving acute doses exceeding 15 kiloGray, ultraviolet, desiccation and oxidative stress due to multilayered defense systems making it uniquely suited for remediation of nuclear weapons production sites like Hanford and Savannah River where organic solvents such as toluene, trichloroethene and heavy metals co-contaminate radionuclide plumes that kill conventional bioremediation bacteria. Resistance mechanisms include

Ref: Brim et al. Nature Biotechnology 2000 Engineered D. radiodurans for radioactive waste; Cox & Battista 2005 Repair review; PubMed radiodurans bioremediation.

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Bioremediation

White rot fungi degrade hydrocarbons using:

White rot fungi including Phanerochaete chrysosporium, Trametes versicolor and Pleurotus ostreatus possess unique extracellular oxidative lignin-degrading machinery evolved to depolymerize wood lignin polymer composed of phenylpropanoid units linked via ether and carbon-carbon bonds, which serendipitously attacks structurally similar persistent organic pollutants including benzo[a]pyrene, polychlorinated biphenyls, dioxins and pentachlorophenol. Key enzymes secreted under nutrient nitrogen limitation triggering secondary metabolism are lignin peroxidase LiP isoenzymes oxidizing veratryl alcoho

Ref: Pointing White rot fungi role in bioremediation Applied Microbiology Biotechnology 2001; Wesenberg et al. lignin peroxidase mechanism; PubMed PAH fungal.

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Bioremediation

Which microorganism is known to degrade aromatic hydrocarbons?

Pseudomonas putida strains such as KT2440 certified HV1 safety, mt-2 and F1 embody archetypal aerobic degraders of monoaromatic and polycyclic aromatic hydrocarbons due to extraordinary metabolic versatility conferred by large genome 6.2 megabases encoding more than 80 oxygenases and multiple catabolic plasmids including TOL plasmid pWW0 carrying upper pathway xylCMABN converting toluene and xylene to benzoate via xylene monooxygenase multicomponent system and meta-cleavage lower pathway xylXYZLTEGFJKIH, and NAH7 plasmid encoding naphthalene dioxygenase nahAc. Enzymatic repertoire includes tol

Ref: Timmis Pseudomonas putida review Nature Reviews Microbiology 2002; EPA aromatic degraders guide; PubMed KT2440 genome PMID 12055322.

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Bioremediation

Bioreactors used in bioremediation are:

Bioreactors in bioremediation function as engineered controlled systems where dissolved oxygen via sparging, agitation 100 to 500 rpm, pH 6 to 8 via dosing, temperature 20 to 35 Celsius via jackets, retention time 0.5 to 10 days, redox potential via ORP probes, and nutrient supply precisely manipulated via controllers maximizing degradation kinetics modeled by Monod equations. Configurations include stirred-tank slurry reactors 10 to 30 percent solids, packed-bed biofilters with immobilized biofilm for air and water, fluidized beds using sand carriers enhancing retention above 10 g per L, and

Ref: Chisti Bioreactors in Waste Management; EPA Bioreactor Design Manual 2002; Wang et al. Bioprocess Engineering principles.

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Bioremediation

Composting as a bioremediation method uses:

Composting as bioremediation modality exploits thermophilic and mesophilic microbial consortia developing during controlled decomposition of organic matter to co-metabolize and mineralize hazardous contaminants such as explosives trinitrotoluene, polycyclic aromatic hydrocarbons, chlorinated pesticides and petroleum hydrocarbons. System typically configured as aerated static windrows or mechanically turned piles where contaminated soil blended at 10 to 30 percent by volume with organic amendments including manure supplying nitrogen, straw providing carbon and structure, wood chips increasing p

Ref: Williams et al. Compost remediation of explosives 1992; EPA Composting Handbook; PubMed compost bioremediation mechanisms.

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