PROCESOS DE TRANSFORMACIÓN DE CONTAMINANTES

HIDRÓLISIS

FOTÓLISIS

OXIDACIÓN-REDUCCIÓN TRANSFORMACIÓN MICROBIANA

TRANSFORMACIÓN EN

ORGANISMOS SUPERIORES

BIOREMEDIATIONBIOREMEDIATION

Bioremediation is the use of biological systems (mainly microoganisms) for the removal of pollutants from aquatic or terrestrial systems. It is based on the extremely diverse metabolic potential of natural microbial communities. A challenge in this area is the existence of xenobiotics, i.e. compounds produced by chemical synthesis for industrial or agricultural purposes and having no counterparts in the natural world. It may be possible to remove bottlenecks in environmental cleanup by selecting soil microorganisms which have developed new properties in response to the introduction of xenobiotics, and then combining different metabolic activities in the same microorganisms for the degradation of a particular target compound.

“In situ”: polluted soil is treated in its original place

“Ex situ”: polluted soil is removed and treated somewhere else

Bioremediation may include the introduction of microorganisms (bioaugmentation), ventilation and/or, adding nutrient solutions (biostimulation)

EVOLUTION OF MICROBIAL WORLD

Microorganisms are the most versatile and adaptable forms of life on Earth, and they have existed here for some 3.5 billions years. For the first 2 billions years of their existence, bacteria alone ruled the biosphere, colonizing every accessible ecological niche from glacial ice to the hydrothermal vents of the deep sea bottoms

What they did?

-Developed the major metabolic pathways characteristic of all living organism today

-Changed earth transforming its anaerobic atmosphere to one rich in oxygen

-Created an environment to sustain more complex forms of life

-Adapted to an even-changing world leading to selection of new metabolic activities

4 weeks, light

4 weeks, dark

Original oil

Time (min)

10:00 30:00 50:00 70:00

Pr Ph

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C18

C15

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C20 C22

C24

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Time (min)

4 weeks, dark

Topped-off oil

PrPh

10:00 30:00 50:00 70:00

a

b

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4 weeks, light

C17

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C18C20 C22

C24

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unresolved hump

unresolved hump

Biodegradability of a substituted aromatic compounds is affected by the modification or removal of one or more substituent groups in order to allow the hydroxylation of two adjacent carbons, followed by the ring cleavage.

 

Factors which affect biodegradabilityFactors which affect biodegradability

•chemical structure:

•concentration

•water solubility

•physical properties

•toxicity

•bioavailibility

•pH, pO2, temperature, redox potential

•ionic composition and concentration

•presence of organic and inorganic nutrients

•presence of adequate microbial populations

A) Molecule:

B) Environment:

•polymerization and branching

•presence of hydrolysis resistant bonds

•heterocyclic, aromatic and polycyclic residues

•chloro and nitro substituents

Characteristics Biodegradation effect

Examples

Such synthetic novel compounds produced by chemical synthesis for industrial or agricultural purposes, have no counterparts in the natural world and then are called “xenobiotics”

How to circumvent bottlenecks in environmental cleanup from xenobiotics?

-By selecting soil microorganisms which have developed new properties in response to the introduction of xenobiotics

-By combining different metabolic abilities in the same microorganism for the degradation of a particular target compound

Organism Substrate

Pseudomonas NAPH, PHEN, ANTH

Flavobacteria PHEN, ANTH

Alcaligenes PHEN

Aeromonas NAPH, PHEN

Vibrio PHEN

Beijerenckia NAPH, PHEN, ANTH, BA, B(a)P

Bacillus NAPH

Nocardia PHEN, ANTH

Corynebacteria NAPH

Micrococcus PHEN

BACTERIA CAPABLE OF OXIDIZING PAH

Note: NAPH= naphtalene, PHEN= pheanthrene, ANTH= anthracene, BA= benz(a)anthracene, B(a)P= benzo(a)pyrene

Different genetic mechanisms may be involved in the evolution of metabolic pathways in general and in the process of adaptation of microorganisms to xenobiotic substrates in particular:

i) gene transfer

ii) mutational drift

iii) genetic recombination and transposition

Degradative plasmids code different catabolic segments which probably have been aggregated on a plasmid during the evolution through the recruitment of genes from different microorganisms, leading to the selection of microorganisms with new catabolic abilities.

 

Strategies for the development of Strategies for the development of microorganisms with new degradative abilitesmicroorganisms with new degradative abilites

• Selection of microorganisms from soils or sediments able to degrade environmental pollutants

• “In vivo” creation of hybrid degradative pathways through assembling of pre-existing catabolic segments transferred from one microorganism to another one

• “In vitro” construction of new degradative pathways through genetic engineering

• Avoid the substrate channelling in useless catabolic pathways which produce toxic products.

 

Development of microorganisms able to degrade Development of microorganisms able to degrade recalcitrant compoundsrecalcitrant compounds

Recalcitrant pollutant molecules

Characterization of the catabolic elements with the capacity to transform apolar chloro and

nitroaromatic compounds

Optimization of catabolic elements to increase the transformation efficiency

Development of bacterial strains for the biodegradation of recalcitrant pollutants

Validation of degradative abilities in microcosmos

Bacterial strains able to efficiently degrade recalcitrant pollutants

feedbackfeedback

feedbackfeedback

The problemThe problem

AnalysisAnalysis

OptimizationOptimization

ValidationValidation

SolutionSolution

PREVENTING POLLUTION AND SAVING PREVENTING POLLUTION AND SAVING NON-RENEWABLE RESOURCESNON-RENEWABLE RESOURCES

Another way to protect the environment is to avoid pollution by replacing chemical pesticides and industrial compounds with environmentally friendly substitutes. Examples of environmental prevention include:

• the use of microbial enzymes in activities such as leather processing, textile desizing, the production of washing powders;

• the use of microbial insecticides;

• the use of plant-growth-promoting bacteria to reduce the use of chemical fertilizers;

• the use of microorganisms to control plant pathogens, so as to reduce the use of fungicides and nematocides;

• the use of biopolymers to save non-renewable resources like fossil fuels.