BIOREMEDIATION 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

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 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

CharacteristicsBiodegradation 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

OrganismSubstrate PseudomonasNAPH, PHEN, ANTH FlavobacteriaPHEN, ANTH AlcaligenesPHEN AeromonasNAPH, PHEN VibrioPHEN BeijerenckiaNAPH, PHEN, ANTH, BA, B(a)P BacillusNAPH NocardiaPHEN, ANTH CorynebacteriaNAPH MicrococcusPHEN 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 microorganisms 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 recalcitrant 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 feedback feedback The problem Analysis Optimization Validation Solution Solution

PREVENTING POLLUTION AND SAVING NON-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.