Microbial degradation of xenobiotics

Xenobiotics- Polycyclic compounds, Azo dyes

1. Microbial degradation of xenobiotics Done by: Shruthi k II M.SC MICROBIOLOGY

2. XENOBIOTICS In Bioremediation, sites contaminated with xenobiotics are cleaned up in situ using microorganisms. Petroleum products, aliphatic and aromatic hydrocarbons, solvents, pesticides and metals are reduced. In recent years, a number of compounds previously considered non-biodegradable are being degraded by microbes. Engineered microbes are being used to degrade xenobiotics by metabolic engineering. Microbes can reduce various classes of hydrocarbons.

3. POLYCYCLIC COMPOUNDS PAHs are composed of fused, aromatic rings whose biochemical persistence arises from dense clouds of π-electrons on both sides of the ring structures making them resistant to nucleophilic attack. Pseudomonas spp., Burkholderia cepacia , Sphingomonas spp., Flavobacterium spp., Cycloclasticus spp., and Stenotrophomonas spp., have been proven to metabolize a large number of PAHs. Fungi : Phanerochaete chrysosporium (lignin), Pleurotus spp., Trametes spp., and Bjerkandera spp., Actinomycetes : Gordonia spp., and Rhodococcus spp.,( fluoranthene , pyrene )

4. They possess key enzymes, such as PAH dioxygenase and catechol oxygenase . The effective lignin- and PAH degradation by Phanerochaete chrysosporium is attributed to the nonspecific oxidoreductases secreted by the fungi, among which lignin peroxidase (Lip) and manganese peroxidase ( MnP ) Napthalene : Fused ring bicyclic aromatic hydrocarbon. The aerobic and anaerobic degradation pathways of naphthalene occurs. After the aldolase and hydroxylase reactions, trans-o- hydroxybenzylidenepyruvate ( tHBPA ) is degraded to produce gentisate or catechol . which is further mineralized to carbon dioxide and water.

5. X.X. Zhang, S.P. Cheng, C.J. Zhu, S.L. Sun Microbial PAH-degradation in soil: degradation pathways and contributing factors,

6. Fluorene : Tricyclic aromatic hydrocarbon. Major component of fossil fuels and their derivatives and is also a byproduct of coal-conversion and energy related industries. dioxygenation at C-1, C-2 or at C-3, C-4 extradiol dioxygenase . cis-dihydrodiols undergo dehydrogenation and then meta-cleavage Aldolase and decarboxylation 1-indanone appears to be a substrate for aromatic hydroxylation yielding 3-hydroxy-l-indanone, which is easily mineralized to carbon dioxide and water.

7. PESTICIDES ENDOSULFAN COMPOUNDS: A endosulfan - degrading bacterium (strain ESD) was isolated from soil inoculum after repeated culture with the insecticide as the sole source of sulfur. Mycobacterium species from the mixed culture demonstrates both the oxidative and hydrolytic and sulfur-separation endosulfan -degrading activities. Mycobacterium strain is a Gram-positive rod that forms mostly rough, convoluted and some smoother, cream coloured colonies after 3 d at 28˚C on either tryptic soy agar, or sulfur-free medium with endosulfan .

8. Mycobacterium strain ESD did not degrade endosulfan when sulphate , sulfite or methionine were included in the growth medium in addition to the insecticide. Conversely, endosulfan metabolism was observed in medium when the insecticide was included in the presence of glutathione, 3-(N- mopholino ) propane sulphonic acid (MOPS), dimethyl sulfoxide (DMSO), cysteine and sulfolane . Presumably the sulfite released by this chemical degradation was being utilized for growth. The hydrophobic cell surfaces of Mycobacteria have been proposed to increase contact with the organic matter and therefore with the hydrophobic contaminant.

9. Sulphate -starvation-induced stimulon (SSIS) proteins are thought to play a role in scavenging alternative sulfur sources The absence of endosulfan -degrading activity in the presence of sulphate and the biphasic utilization of sulphate then endosulfan as sulfur sources suggest that the endosulfan degradative activities observed in Mycobacterium strain ESD are part of the SSIS response in this strain.

10. HALOGENATED COMPOUNDS ATRAZINE: Pseudomonas  sp. strain ADP is able to degrade atrazine as a sole nitrogen source and therefore needs an additional carbon and energy source for growth. Besides the typical C source for  Pseudomonas , Na 2 -succinate, the strain can also grow with phenol as a carbon source With atrazine as an N source, the strain was able to degrade phenol in amounts of up to 1,000 mg/liter. At higher concentrations, even completely adapted cells were no longer able to grow.

11. In the presence of cyanuric acid, the strain degraded phenol much faster. At higher concentrations, the toxic effects of phenol seem to reduce the growth rate of the cells. These data showed that it was possible to cultivate  Pseudomonas  sp. strain ADP with phenol as a sole C and energy source and simultaneously with atrazine or cyanuric acid as an N source. Phenol is usually degraded via the catechol degradation pathway. There are two pathways for catechol ring fission, the  meta  and  ortho  pathways  This is the first description of the simultaneous degradation of two hazardous compounds used by a single bacterium as the C and N source, respectively.

12. PETROLEUM HYDROCARBONS Divided into four classes: the saturates, the aromatics, the asphaltenes and the resins. The susceptibility of hydrocarbons to microbial degradation can be generally ranked as follows: linear alkanes   > branched alkanes  > small aromatics  > cyclic alkanes . Bacteria: Arthrobacter , Burkholderia , Mycobacterium, Pseudomonas, Sphingomonas , and Rhodococcus and 25 other genera. Fungi:   Talaromyces , and  Graphium   and yeast genera , namely , Candida, Yarrowia , and  Pichia Algae: Prototheca zopf

13. initial intracellular attack of organic pollutants is an oxidative process and the activation as well as incorporation of oxygen is the enzymatic key reaction catalyzed by oxygenases and peroxidases . Peripheral degradation pathways convert organic pollutants step by step into intermediates of the central intermediary metabolism, for example, the tricarboxylic acid cycle.

14. Mechanisms involved are (1) attachment of microbial cells to the substrates and (2) production of biosurfactants  . Microbial Degradation of Petroleum Hydrocarbon Contaminants: An Overview by Nilanjana das and Preethy Chandran .

15. Cytochrome P450 alkane hydroxylases play an important role in the microbial degradation of oil, chlorinated hydrocarbons, fuel additives. Yeast: Candida maltosa , Candida tropicalis , and Candida apicola   Alkaneoxygenase systems in prokaryotes and eukaryotes are involved in degradation of alkanes under aerobic conditions. Cytochrome P450 enzymes and membrane-bound copper containing methane monooxygenases  

16. AZO DYES The excessive discharge of the effluents from the textile industries contains toxic chemicals such as azo dyes affect the natural resources. It increases the biochemical oxygen demand (BOD) and chemical oxygen demand (COD). Azo dyes are the largest class of synthetic aromatic dyes composed with one or more ( N=N ) groups and sulfonic (-SO 3 groups. Generally, azo dyes contain one, two or three azo linkages, linking phenyl, naphthyl rings that are usually substituted with some functional groups including triazine amine, chloro , hydroxyl, methyl, nitro, and sulphonate

17. 10% of the dyes used in dyeing process do not bind to the fiber and are released into the environment. They possess toxicity like lethal effect, genotoxicity , mutagenicity , and carcinogenicity to plants and animals. Microorganism can be used to completely degrade the azo dyes, because microorganisms reduce the azo dyes by secreting enzymes such as laccase , azo reductase , peroxidase , and hydrogenase .

18. Non-specific degradation Bacteria: Bacilus subtilis , Pseudomonas sp, Escherichia coli, Rhabdobacter sp, Enterococcus sp, Staphylococcus Used as sole source of carbon and nitrogen and others reduce azo dyes by oxygen tolerant azo reductases . Azo dyes are not readily metabolized under aerobic condition and are degraded into intermediate compounds but not mineralized. Aerobic- anaerobic coupled reaction. M.Sudha , A.Saranya , G. Selvakumar and N. Sivakumar Microbial degradation of Azo Dyes: A review

19. Fungi : Phanerochaete chrysosporium , Rhizopus oryzar , Pleurotus ostreatus , Rigidoporus lignosus , Pycnoporus sanguineus , Aspergillus flavus , and Aspergillus niger . White-rot fungi produces lignin peroxidase , manganese peroxidase and laccase that degrades many aromatic compounds. Lignin peroxidase plays a major role in the degradation of azo dyes using P. chrysosporium

20. REFERENCES X.X. Zhang, S.P. Cheng, C.J. Zhu, S.L. Sun Microbial PAH-degradation in soil: degradation pathways and contributing factors, Pedosphere , 16 (2006), pp. 555-565 Sutherland TD, Home I, Harcourt RL, Russel RJ and Oakeshott JG (2002) Isolation and characterization of a  Mycobacterium  strain that metabolizes the insecticide endosulfan . J Appl Microbiol 93:380–389 Microbial Degradation of Petroleum Hydrocarbon Contaminants: An Overview by Nilanjana das and Preethy Chandran . M.Sudha , A.Saranya , G. Selvakumar and N. Sivakumar Microbial degradation of Azo Dyes: A review, Int.J.Curr.Microbiol.App.Sci (2014) 3(2): 670-690